HomeMy WebLinkAboutCT 13-03; ROBERTSON RANCH WEST VILLAGE; AS GRADED REPORT OF MASS GRADING; 2016-06-28LGC Valley, Inc.
Geotechnical Consulting
AS-GRADED REPORT OF MASS GRADING,
PLANNING AREAS PA-1 THROUGH PA-3, PA-5,
PA-6, PA-9, PA-b, PA-13 AND PA-23A
THROUH PA-23C, ROBER TSON RANCH,
CARSLBAD TRA CT NO.13-03,
CARLSBAD, CALIFORNIA
Project No. 133023-03
Dated: June 28, 2016
Prepared For:
Toll Brothers
725 Town and Country Road, Suite 200
Orange, California 92868
2420 Grand Avenue, Suite F2 • Vista • CA 92081 • (760) 599-7000 • Fax (760) 599-7007
LGC Valley, Inc.
Geotechnical Consulting
June 28, 2016
Mr. Kevin Brickley
Toll Brothers
725 Town and Country Road, Suite 200
Orange, California 92868
ProjectNo. 133023-03
Subject: As-Graded Report of Mass Grading, Planning Areas PA-1 through PA-3, PA-5, PA-6, PA-9,
PA-b, PA-13, and PA-23A through PA-23C, Robertson Ranch, Carlsbad Tract No. 13-03,
Carlsbad, California, California
In accordance with your request and authorization, LGC Valley, Inc. (LGC) has provided geotechnical services
during the mass grading operations for Planning Areas PA-i through PA-3, PA-5, PA-6, PA-9, PA-b, PA-13,
and PA-23A through PA-23C of the Robertson Ranch project (Carlsbad Tract No. 13-03) located within the
City of Carlsbad, California. Planning Areas PA-1 and PA-23A through PA-23C are open space areas; PA-2 is
the site of a future community facility; while PA-3, PA-5, PA-6, PA-9, PA-10, and PA-13 are single-family
residential developments. Planning Areas PA-3, PA-5, PA-6, PA-9, PA-b, and PA-13 consist of a total of 308
single-family residential lots; 34 Home Owner Association (HOA) lots comprising landscape areas, storm
water retention basins, and community recreational areas; streets; slopes; and associated improvements. The
accompanying as-graded report of mass grading summarizes our observations, field and laboratory test results,
and the geotechnical conditions encountered during grading of the subject site.
The mass grading operations for Planning Areas PA-b through PA-3, PA-5, PA-6, PA-9, PA-b, PA-13, and
PA-23A through PA-23C of the Robertson Ranch project were performed in general accordance with
previously published project geotechnical reports (Appendix A), geotechnical recommendations made during
the course of grading, and the City of Carlsbad grading requirements. It is our professional opinion that the
subject site is suitable for its intended use provided the recommendations included herein and in the project
geotechnical reports are incorporated into the fine/precise-grading, design, and construction of the proposed
development and associated improvements. As of the date of this report, the mass grading operations of the
subject site are essentially complete.
If you have any questions regarding our report, please contact this office. We appreciate this opportunity to be
of service.
Respectfully Submitted,
LGC Valley, Inc.
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Randall Wagner, CEG 1612
Senior Project Geologist
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Basil Hattar, GE 2734
Principal Engineer
Distribution: (6) Addressee
2420 Grand Avenue, Suite F2 • Vista • CA 92081 • (760) 599-7000 • Fax (760) 599-7007
TABLE OF CONTENTS
Section
1.0 INTRODUCTION...................................................................
1.1 Project Description.....................................................
2.0 SUMMARY OF MASS-GRADING OPERATIONS..............
2.1 Site Preparation and Removals...................................
2.2 Saturated Alluvial Mitigation.....................................
2.3 Stability Fills...............................................................
2.4 Subdrain Installation...................................................
2.5 Fill Slope Keys............................................................
2.6 Cut/Fill Transition Conditions....................................
2.7 Overexcavation of Cut Lots.........................................
2.8 Toxaphene Impacted Soil Removal and Burial............
2.9 Fill Placement and Compaction..................................
2.10 Laboratory Testing......................................................
2.11 Field Density Testing..................................................
2.12 Graded Slopes.............................................................
2.13 Settlement Monuments ................................................
2.14 Verdura Retaining Walls.............................................
2.15 Animal Crossing on Gage Drive .................................
3.0 ENGINEERING GEOLOGIC SUMMARY..........................
3.1 As-Graded Geologic Conditions .................................
3.2 Geologic Units............................................................
3.3 Geologic Structure......................................................
3.4 Faulting and Seismicity ...............................................
3.4.1 On-Site Faulting...........................................
3.5 Ground Water.............................................................
4.0 CONCLUSIONS.....................................................................
4.1 General.......................................................................
4.2 Summary of Conclusions............................................
5.0 RECOMMENDATIONS........................................................
5.1 Earthwork...................................................................
5.2 Site Preparation .........................................................
5.3 PA-2 Future Work......................................................
5.4 Excavations ................................................................
5.5 Fill Placement and Compaction.................................
5.6 Foundation Recommendations...................................
5.7 Subdrain Outlet Maintenance ....................................
5.8 Control of Surface Water and Drainage....................
6.0 LIMITATIONS.......................................................................
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Project No. 133023-03 Page i June 28, 2016
LIST OF TABLES, ILLUSTRATIONS, AND APPENDICES
Figures and Plates
Figure 1 - Site Location Map (Page 2)
Plates IA through IF - As-Graded Geotechnical Map (Rear-of-Text)
Plates 2A through 2F - Field Density Test Location Map (Rear-of-Text)
Appendices
Appendix A - References
Appendix B - Laboratory Testing Procedures and Test Results
Appendix C - Summary of Field Density Test Results
Project No. 033024-01 Page ii June 28, 2004
1.0 INTRODUCTION
In accordance with your request and authorization, LGC Valley, Inc. (LGC) has provided geotechnical
services during the mass grading operations for Planning Areas PA-i through PA-3, PA-5, PA-6, PA-9,
PA-b, PA-13, and PA-23A through PA-23C of the Robertson Ranch project (Carlsbad Tract No. 13-
03) located within the City of Carlsbad, California. This as-graded report of mass grading summarizes
our observations, field and laboratory test results, and the geotechnical conditions encountered during
grading of the subject site. Planning Areas PA-4, PA-7, PA-8, and PA-il of Robertson Ranch were
graded at the same time as the remainder of the site but are not included in this report. The results of
our geotechnical observation and testing services, as well as, our conclusions and recommendations
concerning the as-graded conditions of PA-4, PA-7, PA-8, and PA- li of Robertson Ranch have or will
be presented under separate cover.
The mass grading operations for Planning Areas PA-i through PA-3, PA-5, PA-6, PA-9, PA-b, PA-
13, and PA-23A through PA-23C of the Robertson Ranch project were performed in general
accordance with previously published project geotechnical reports (Appendix A), geotechnical
recommendations made during the course of grading, and the City of Carlsbad grading requirements.
As of this date, the mass grading operations for the subject areas are essentially complete.
The Rough Grading Plans for the Robertson Ranch project, prepared by O'Day Consultants (O'Day,
2014a), were utilized as a base map to present the as-graded geotechnical conditions and approximate
locations of the field density tests. The As-graded Geotechnical Map (Plates 1A through IF) and the
Field Density Test Location Map (Plates 2A through 2F) are presented in the pocket at the rear of the
text.
1.1 Project Description
The Robertson Ranch development is approximately 211 acres in size and is located on the
north side of El Camino Real between Tamarack Avenue on the west and Cannon Road on
the east in the northeastern portion of the City of Carlsbad, California. The irregular-shaped
site is bounded by El Camino Real on the south, Tamarack Avenue on the northwest,
existing residential developments on the north and east, and by Cannon Road on the
southeast.
The proposed Robertson Ranch development consists of a number of Planning Areas
including PA-I through PA-11, PA-I3, and PA-23A through PA-23C. Based on our
understanding, PA-i and PA-23A through PA-23C are designated open spaces areas; PA-2
will be a future community facility; PA-3, PA-S, PA-6, PA-9, PA-b, and PA-13 are single-
family residential communities; PA-4 will be a community center and pool complex; PA-7
and PA-8 will be a multi-family residential development with an assisted-living senior
housing center; and PA- li will be a retail/commercial site.
Project No. 133023-03 Page 1 June 28, 2016
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Project Name Toll Brothers/Robertson Ranch Figure 1 Project No. 133023-03
Site Location Map Eng. / Geol. BIH/RKW
Robertson Ranch Scale not to scale
City of Carlsbad, California Date June 28, 2016
Development of Planning Areas PA-i through PA-3, PA-5, PA-6, PA-9, PA- 10, PA- 13, and
PA-23A through PA-23C of the Robertson Ranch project includes:
308 single-family residential lots (Lots I through 23 of Planning Area PA-13; Lots 25
through 60 of Planning Area PA-5; Lot 63 through 149 of Planning Area PA-3; Lots 158
through 244 of Planning Area PA-6; Lots 252 through 298 of Planning Area PA-9; and
Lots 299 through 326 of Planning Area PA-b);
34 HOA lots consisting of landscape areas; storm water retention basins (Lots 24, 61, 62,
150 through 153, 155, 157, 246 through 251, 328, and 329); and community recreational
areas (Lots 154, 156, 245, and 330);
Associated streets (West Ranch Street, Gage Drive, Robertson Road, Wadsworth Street,
Wellspring Street, Borden Court, Crespi Court, Kentner Court, Chase Court, Portola
Court, Nelson Court, La Paz Court, Trailblazer Way, and a portion of Glasgow Drive and
Edinburgh Drive);
Manufactured fill and cut slopes around the perimeter of the lots and streets;
A sheet-graded pad for a future community facility on Planning Area PA-2; and,
Undeveloped open space areas within Planning Areas PA-i and PA-23A through PA-
23C.
We anticipate the site construction to consist of residential structures, driveways,
underground utility services, retaining walls, concrete flatwork, landscaping, etc. We
understand the residential structures will be up to two-stories in height and have slab-on-
grade with wood-frame and stucco construction.
Project No. 133023-03 Page 3 June 28, 2016
2.0 SUMMARY OF MASS-GRADING OPERATIONS
Mass grading of the subject site began on September 15, 2014 and was essentially completed as of May
15, 2015. The grading operations were performed under the observation and testing services of LGC
Valley, Inc. Our field technicians were onsite on a full-time basis during the grading operations while
our field and project geologists were on-site on a periodic basis. The mass-grading operations included:
Removal and off-site disposal of vegetation and miscellaneous debris;
The removal of potentially compressible soils including alluvium, colluviuni, topsoil,
undocumented fill, and weathered soils to competent terrace deposits or formational material;
Overexcavation of cut/fill transition conditions within the limits of the residential lots;
Overexcavation of buried cut/fill transition conditions such that the resulting fill differential
beneath the proposed building pads was less than a 3:1 (maximum fill thickness to the
minimum fill thickness);
Overexcavation of cut lots due to expansive soils lots and/or very dense moderately cemented
sandstone;
The excavation of stability fill keys;
Preparation of areas to receive fill;
The placement of subdrains in the canyon bottoms and along the heel of the stability fill
keys;
Installation of stabilization fabric and rock layer over left-in-place saturated alluvium;
The placement of compacted fill soils and excavation of cut creating the lots, streets, sheet-
graded pads and adjacent slopes; and
Installation of settlement monuments in deep fill areas (considered to be fills greater than
40 feet below design finish grades).
The mass-grading operations consisted of the excavation of up to approximately 50 feet of cut and
placement of a maximum thickness of approximately 75 feet of fill. The as-graded geotechnical
conditions are presented on the As-Graded Geotechnical Map (Plates 1A through IF).
2.1 Site Preparation and Removals
Prior to grading, the site was cleared of light vegetation, trash, prior farming debris, and other
miscellaneous debris and the material was disposed of at an offsite facility. Undocumented fill,
topsoil, alluvium, colluvium, weathered terrace soils, and formational material were removed to
competent material (i.e. dense unweathered terrace or formational material). Remedial
removals on site, below the existing ground surface, generally ranged from approximately 3 to
15 feet with a maximum depth of remedial removal of up to approximately 40 feet associated
with the main north-south trending canyons in the southwestern and southeastern portions of
PA-7 and in the central portion of PA-8.
Following the remedial removals or overexcavations, areas to receive fill were scarified
approximately 6- to 12-inches; moisture-conditioned, as needed, to obtain a near-optimum
Project No. 133023-03 Page 4 June 28, 2016
moisture content; and compacted to a minimum 90 percent relative compaction (for fills of
approximately 40 feet or less from design grades) or 93 percent relative compaction (for
engineered fill below approximately 40 feet from design finish grades). Compaction was
determined by ASTM Test Method D6938 (i.e. the nuclear gauge method).
2.2 Saturated Alluvial Mitij!ation
Based on geologic mapping and observations made during the remedial grading removals
within Planning Area PA-2 and in the northwestern portion of Robertson Road (between
approximate Station Number 10+50 and 12+25), shallow groundwater was encountered at an
approximate depth of 5 to 6 feet below the existing ground surface within the alluvial soils.
This ground water condition is assumed to be a perched ground water within the lower section
of the on-site alluvial soils. Recommendations were made to remove the alluvial soils to within
1 to 2 feet of the groundwater elevation, install a stabilization fabric (i.e. Mirafi 600x) along the
removal bottom and then place sandy compacted fill to the design grades (LGC, 2015). In areas
where standing water was present or where significant pumping and rutting occurred, a 1- to 2-
foot thick rock layer was placed in the removal bottom prior to the placement of the
stabilization fabric. The rock layer consisted of 6-inch minus rock with sand.
The approximate locations of the rock layer and stabilization fabric include the west side of
Robertson Road between Station 10+65 and 12+85; and the north-central and northeast side of
PA-2. The approximate locations of the stabilization fabric include the east side of Robertson
Road between Station 10+65 and 12+30, the west side of Robertson Road between Station
12+85 and 14+00, and the southeast side of PA-2.
2.3 Stability Fills
Stability fills were constructed to stabilize the exposed blocky claystone/siltstone and/or
adverse (i.e. out-of-slope) geologic conditions present within the Santiago Formation. The
stability fill keys were excavated to a width ranging from 15 to 25 feet and a minimum depth of
3 to 5 feet below the toe-of-slope. The keyway bottom was angled at least 2 percent into-the-
slope. The stability fill front cuts were excavated near vertical while the backcuts were
excavated at an approximate 2:1 or 1:1 (horizontal to vertical) slope inclination. Subdrains were
places along the heel of the stability fill keys and are discussed in Section 2.4.
Stability fills were excavated along the proposed slope on; 1) the northeast sides of Lots 68
through 70 of PA-3; 2) the north sides of Lots 92 through 95 of PA-3; 3) south of Lots 135
through 145, 156, and 157 of PA-3; 4) the northwest sides of Lots 158 through 163 and 245 of
PA-6; 5) the northwest sides of Lots 170 through 182 of PA-6; 6) southeast of Lots 185 through
193 of PA-6; 7) southeast and east of Lots 198 through 210 of PA-6; 8) the west side of Lots
212 through 223 of PA-6; 9) the north side of Lots 252 through 264, 277 through 281, and 282
through 286 of PA-9; 10) the north side of Lots 300, 301 and 328, 302 through 307 and 329,
317 through 319, and 320 through 323 of PA-l0; 11) the east side of Robertson Road between
approximate Station No. 15+75 to 18+00 in PA-1; and 12) the north side of PA-11. The
Project No. 133023-03 Page 5 June 28, 2016
approximate locations of the stability fill keys are presented on the As-graded Geoteclmical
Map (Plates 1A through IF).
The stability fill keys recommended in the project preliminary geotechnical report (LGC,
2014a) on the north sides of Lots 82 through 87 and 150; Lots 88 through 91 and 151; Lots 107
through 110 and 152; Lots iii through 114 and 153; Lots 127 through 130 and 154; and Lots
131 through 134 and 155 were not constructed during the mass grading operations. Instead, the
slopes on these lots were completely overexcavated removing the proposed cut and replacing
the slopes with compacted fill. The overexcavation extended to a depth of at least 5 feet below
the proposed toe-of-slope with a removal bottom angled no steeper than a 3:1 (horizontal to
vertical).
2.4 Subdrain Installation
Canyon and stability fill subdrains were installed under the observation of a representative of
LGC in general accordance with the approved geotechnical report (LGC, 2014a) and
geotechnical recommendations made during the course of the mass grading operations. After
the potentially compressible material in the canyons were removed to competent material or
when compacted fill was placed over competent material to obtain flow to a suitable outlet
location, a subdrain was installed along the canyon bottom. The canyon subdrains consisted of
a 6-inch diameter perforated pipe surrounded by a minimum of 9-cubic feet (per linear foot) of
crushed 3/4-inch gravel wrapped in Mirafi 140N filter fabric. Canyon subdrains were installed
in the western canyon along the east side of PA-3; in the small canyon in the middle of PA-7;
the main canyon in PA-5 through PA-8; the upper end of the south canyon in PA- 11; and in the
two small canyons in the southeast portion of PA-b.
In addition to the canyon subdrains, subdrains were also installed along the bottom backside of
the stability fill keys. The stability fill subdrains consisted of a 4-inch diameter perforated pipe
surrounded by a minimum of 3-cubic feet (per linear foot) of clean 3/4-inch gravel wrapped in
Mirafi 140N filter fabric. Stability fill key subdrains were installed in each of the keys
mentioned in Section 2.3.
The canyon and stability fill subdrains were placed with a minimum i-percent fall (2-percent or
greater where possible) to a suitable outlet location. The locations of the subdrains placed
during the mass-grading operations for the project were surveyed by the project civil engineer.
The subdrain locations are presented on the As-graded Geoteclmical Map (Plates IA through
iF).
As indicated on the as-graded geotechnical map, three (3) canyon subdrains and five (5)
stability fill subdrains were ultimately outletted into adjacent storm drain structures or the storm
drain pipe. Four of these outletted subdrains are located on the north side of El Camino Real
(on the south side of Planning Area PA-3) and four are located along Gage Drive in Planning
Areas PA-9 and PA-b.
Project No. 133023-03 Page 6 June 28, 2016
2,5 Fill Slope Keys
Prior to the placement of fill slopes that were planned above natural and/or cut areas on the site,
a fill slope key was constructed. The fill slope keys were excavated at least 2 feet into
competent soil along the toe-of-slope and constructed approximately 15 feet wide with the key
bottom angled a minimum of 2 percent into-the-slope. Fill slope keys constructed on site during
the mass grading operations included the slopes: 1) northwest of Lots 63, 71, and 82 of PA-3;
2) east of Lots 226 through 243 of PA-6; 3) west of Lots 252, 265, 276, and 288 of PA-9 and
Lots 299, 308, 317, and 325 of PA-TO; 4) east of Edinburgh Drive, Lots 275, 287, and 298 of
PA-9 and Lots 307, 316, 324, and 330 of PA-10; and 5) the west side of Robertson Road
approximately from Station 14+00 to 15+90 west of PA-3.
2.6 Cut/Fill Transition Conditions
The cut portion of lots that exposed the cut/fill transition was overexcavated a minimum of 5
feet below finish pad grade. Overexcavation of the building pad was performed to mitigate the
transitional condition and related adverse effects of differential settlement that can result due to
this underlying condition. The limits of the overexcavations were made at least 5 feet outside
the anticipated building limits (or building footprint). To reduce the potential of a perched
ground water condition within the transition lots, the pads were overexcavated with a minimum
1-percent fall in the overexcavation bottom toward the fill. During the mass grading operations,
remedial grading was also performed so that the fill differential beneath the proposed building
pads was less than a 3:1 (maximum fill thickness to the minimum fill thickness).
Lots that were overexcavated due to a cut/fill transition condition include Lots 29 through 32,
48, and 54 of PA-5; Lots 63, 68, 69, 71, 72, 77, 82, 88, 100, 112, 124, 133, and 135 through 145
of PA-3; Lots 164, 165, 169 through 171, 189, 198 through 207, and 226 through 244 of PA-6;
Lots 252, 253, 266 through 269, 275, 277 through 279, 287, 294, and 295 of PA-9; and Lots
300, 301, 305 through 307, 309 through 312, 317, 318, and 323 of PA-b.
2.7 Overexcavation of Cut Lots
During the mass grading of the Robertson Ranch project, the overexcavation of cut lots was
performed in order to mitigate potential adverse conditions including: 1) well-cemented
sandstone beds (or concretion layers) and very dense or hard Santiago Formation at or near
finish grade which could create difficulties during future excavations on the lots; and 2)
potential highly expansive soils at finish grade that would require significant post-tension
foundation designs. The cut lots that contained these conditions were overexcavated a
minimum of 5 feet below finish pad grade and replaced with compacted fill. In order to
minimize potential ponded ground water conditions on the overexcavation bottom, the lots
were overexcavated with a minimum fall of 1- to 2-percent toward the front of the lot or deeper
fill area.
Project No. 133023-03 Page 7 June 28, 2016
Lots overexcavated due to well-cemented sandstone or dense Santiago Formation included Lots
39 through 47 and 60 of PA-5; and Lots 158 through 163, 183, 184, 212, and 213 of PA-6. Lots
overexcavated due to expansive clayey soils included Lots 64 through 67, 70, 73 through 76,
83 through 87,92 through 99, 105 through 111, 115 through 123, and 127 through 132 of
PA-3; Lots 180 through 182 of PA-6; Lots 254 through 264, 270 through 274, 280 through
286, 292, 293 of PA-9; and Lots 319 through 322 of PA-b.
2.8 Toxaphene Impacted Soil Removal and Burial
Previous studies by GeoSoils (GeoSoils, 2007b, 2007c, 2010a, 2010b, 2010c, and 2011b),
indicated that approximately 95,000 cubic yards of pesticide impacted soils were present on the
site and that these soils needed to be remediated during the mass grading operations. The
County of San Diego Department of Environmental Health (DEH) was the review and approval
agency and the case opened in March 2011 as "Rancho Costera, El Camino Real and
Tamarack, Carlsbad"; DEH File No. H39768-001. Documents related to the case can be found
on the web site "Geotracker" using the case file number on the advanced search page of the
site. The site can be found at "geotracker.waterboards.ca.gov".
Based on the approved site Property Mitigation Plan (PMIP), the proposed mitigation measures
included the excavation of the toxaphene impacted soil and placement of the soils within the
on-site street right-of-ways in planned fill areas (Havasu Consulting, 2014). The approved PMIP
presented a remediation approach to remove the toxaphene impacted soil where concentrations
existed at or above 460 jig/kg (i.e. the threshold value requiring remediation) within the
property. The PMP also presented an approach designed to place the toxaphene impacted soils
in designated areas within the street right-of-ways of the site at depths greater than 12 feet
below the finish surface of the street or 2 feet below the deepest utility (if the utility line was
greater than 10 feet in depth). Based on the highest anticipated groundwater elevation of
approximately 45 feet mean sea level (MSL), no impacted soil was to be placed below an
elevation of 50 feet MSL, thereby providing a minimum soil cap of 5 feet above the highest
anticipated groundwater elevation. A marker material was to be placed over the final level of
toxaphene-impacted soil to identi the location of the impacted soil.
Based on soil sampling results from previous subsurface investigations (Havasu Consulting,
2014), soils to depths from 0 to 4 feet below the ground surface were expected to be impacted
above the site clean-up level. Nine (9) designated areas (i.e. Areas A through I) on the site were
identified by GeoSoils as being impacted with toxaphene. Remedial excavation work
commenced on September 29, 2014 and was completed by November 7, 2014. The remediation
operations typically consisted of: 1) one dozer and a water truck ripping and moisture-
conditioning the impacted soil removal areas prior to removal; 2) three to six scrapers
excavating the impacted soil and hauling it to the burial areas; and 3) the same dozer and/or a
second dozer, the same water truck and the scrapers mixing the soil, adding additional water,
and compacting the soil to the project geotechnical recommendation of 90 percent relative
compaction. Observation and field density testing of the compacted soil was performed by a
senior, field technician from LGC (Havasu, Consulting, 2016).
Project No. 133023-03 Page 8 June 28, 2016
The excavated impacted soils were placed in three burial areas on the site in the south and
central portions of the site and included a portion of West Ranch Street; Robertson Road;
Wellspring Street; and Nelson Court. Upon completion of the burial areas, the tops and upper
sides of the impacted soil was covered with a dark gray filter fabric. Prior to the placement of
the impacted soil and after the fabric was placed, the burial areas were surveyed by the project
civil engineer. The approximate limits of the burial locations are shown on the As-Graded
Geotechnical Map (Plates 1A through IF). A comprehensive discussion of the toxaphene
impacted soil remediation operations is presented in the report entitled "Final Remedial
Summary Report", dated March 31, 2016 (Havasu Consulting, 2016).
Upon the completion of the impacted soil removals in the nine removal areas, random
verification/confirmation sampling was performed. The test results demonstrated that: 1) the
toxaphene levels at the base of the removal excavations were non-detected or below the
threshold values requiring remediation; and 2) that the toxaphene-impacted soil was removed.
Subsequent to the grading of the site in the areas of the previously impacted soil and burial
areas, 15 random post-grading soil samples were obtained and tested for toxaphene. The test
results indicated the samples did not detect any toxaphene (Havasu Consulting, 2016).
2.9 Fill Placement and Compaction
After processing the areas to receive fill, native soil was generally spread in approximately 8-
inch loose lifts, moisture-conditioned as needed to attain near-optimum moisture content, and
compacted to at least 90 or 93 percent of the maximum dry density determined in accordance
with ASTM Test Method .D1557. Fill soils less than 40 feet below the design finish grades
were compacted to a minimum 90 percent relative compaction while fill soils greater than 40
feet below the design finish grades were compacted to a minimum 93 percent relative
compaction. Compaction was achieved by use of heavy-duty construction equipment. Areas of
fill in which either field density tests indicated less than 90 or 93 percent relative compaction or
the soils exhibited nonuniformity and/or showed an inadequate or excessive moisture content,
were reworked, recompacted, and retested until a minimum 90 or 93 percent relative
compaction and near-optimum moisture content was achieved.
2.10 Laboratory Testin'
Maximum dry density tests of representative on-site soils were performed (by others during the
previous investigation and by LGC during the current mass-grading operations) in general
accordance with ASTM Test Method D1557. Representative expansion potential, soluble
sulfate content, and corrosion suite tests were performed on representative samples of the finish
grade soils on the residential lots.
The test results indicate the representative finish grade soils have: 1) a very low to high
expansion potential (per U.B.C. Standard No. 18-I-B); 2) a negligible to severe soluble sulfate
content per ACI criteria (ACI 318R-08 Table 4.3.1); 3) are moderately to severely corrosive to
buried metals based on the minimum soil resistivity values; and 4) are corrosive to buried
Project No. 133023-03 Page 9 June 28, 2016
metals and reinforcing steel in concrete based on the chloride concentrations. The laboratory
test procedures and laboratory test results are presented in Appendix B.
2.11 Field Density Testinji
Field density testing was performed using the Nuclear-Gauge Method (ASTM Test Method
D6938). The approximate test locations are shown on the Field Density Test Location Map
(Plate 2). The results of the field density tests are summarized in Appendix C.
The field density testing was performed in general accordance with the applicable ASTM
standards and the current standard of care in the industry. In-situ soil density testing is
intended to verify the effectiveness of the earthmoving operation in general and is performed
on a spot-check basis; as such, some variations in relative compaction should be expected
from the results documented herein.
2.12 Graded Slopes
Manufactured fill and cut slopes within the subject area were surveyed by the civil engineer and
constructed with slope inclinations of 2:1 (horizontal to vertical) or flatter. Permanent graded
fill slopes within the subject area range from less than 5 to approximately 90 feet in height.
Permanent cut slopes are approximately 5 to 10 feet in height or less.
The on-site fill and cut slopes are considered grossly and surficially stable from a geotechnical
standpoint (under normal irrigation/precipitation patterns) provided the project geotechnical
recommendations are incorporated into the fine-grading, post-grading, construction, and
post-construction phases of site development.
2.13 Settlement Monuments
The compacted fills within Robertson Ranch range from 0 to approximately 75 feet in depth.
A total of seven settlement monuments were installed/constructed at representative locations
in the deep fill areas in general accordance with the project geotechnical report (LGC,
2014a), following the completion of the majority of fill placement operations in the deep fill
areas. However, five of these settlement monuments were placed within deep fill areas of
PA-7 and PA-8. The settlement monuments were installed in deep fill areas ranging from 50
to 75 feet in thickness. The approximate location of the settlement monuments are shown on
the As-Graded Geotechnical Map (Plates IA through IF).
The settlement monuments were surveyed by O'Day Consultants. Based on the settlement
monument readings to date of the two monuments in Planning Area PA-6 and in Gage Drive
between Planning Areas PA-6 and PA-10 (i.e. Settlement Monuments 46 and #7), settlement
of the fills has been minimal. Based on almost 14 months of survey readings, the settlement
of the deep fill in the vicinity of Settlement Monument #6 is less than 1/10-inch of
Project No. 133023-03 Page 10 June 28, 2016
settlement. In the vicinity of Settlement Monument #7, the deep fill has settled about 1/2-
inch over a five (5) month period. The accuracy of the settlement survey readings is +1- 1/4-
inch. As a result, it is our professional opinion that the primary and secondary consolidation
of deep fills is within acceptable limits.
2.14 Verdura Retaining Walls
During the mass grading operations, a number of Verdura mechanically-stabilized retaining
walls were constructed on the site. Prior to the construction of the retaining wall, the footing
excavation and soil conditions was observed by a LGC representative and found to be in
general accordance with the design parameters and recommendations assumed in the project
geotechnical report and retaining wall design parameters (LGC, 2014, 2014c, and 2015j). In
addition, a backdrain was placed along the back bottom side of the retaining wall key and
outletted at the slope face below the wall. Field density testing was also performed during the
backfill operations of the retaining walls. The field density test results indicated that the
backfill soils were compacted to a minimum 90 percent relative compaction (based on
ASTM Test Method D1557). The field density test results are presented in Appendix C.
Verdura retaining walls were constructed at the following locations: 1) above and below the
trail on the southwest and south sides of Lot 92 of PA-3; 2) in the middle of the large south-
facing slope on the south sides of Lots 135 through 145, 156, and 157 of PA-3; 3) in the
middle of the east-facing slope east of Lots 240 through 243 of PA-6; 4) on the northwest
side of the trail adjacent to Lot 34 of PA-5; and 5) on the northwest side of the trail adjacent
to Lot 36 of PA-S.
2.15 Animal Crossing on Gate Drive
As part of the development of the Robertson Ranch project, an animal crossing was proposed
along the bottom of the canyon that a portion of Gage Drive crossed between Planning Areas
PA-6 and PA-10. As designed and built, the structure consists of a 18-foot diameter, 3-gauge
(0.249-inches) thick galvanized Contech "Multi-Plate" Corrugated Metal Pipe Structure with
a design life of at least 100 years. The structure has an approximately 6-foot fall from the
northwest to southeast ends of the pipe (i.e. a fall of approximately 2.5 percent). The
structure is approximately 225 feet in length with cast-in-place concrete headwalls at both
ends and has up to 30 to 35 feet of compacted fill placed over the top of the structure. The
upstream and downstream headwalls are approximately 36 and 27 feet in height,
respectively.
Grading and construction of the structure was started on June 29, 2015 and essentially
completed by November 2015. Prior to the construction of the structure, all of the alluvium
was removed beneath the proposed structure and replaced with sandy fill soils compacted to
either 93 percent relative compaction for the fill soils greater than 40 feet in depth or 90
percent relative compaction for fill soils less than 40 feet from the design finish grade
elevation.
Project No. 133023-03 Page 11 June 28, 2016
A 2-foot thick layer of select material (i.e. 'rock dust' consisting of sand-sized rock chips)
was placed below the bottom of the pipe as a bedding layer. The bottom of this select
material layer was angled approximately 2-percent from west to east. Along the east side of
the animal crossing alignment, a subdrain consisting of a 4-inch diameter perforated pipe
with 4-cubic feet of crushed rock (per linear foot) and surrounded by a Mirafi 140N filter
fabric was placed and outletted into the rock riprap on the downhill (or southeast side) of the
animal crossing. The subdrain has a fall of approximately 2.5 percent.
After the multi-plate corrugated metal pipe was bolted together, the concrete headwalls on
both side of the structure were constructed and allowed to cure. After the curing period, a 2-
foot thick layer of the 'rock dust' was placed and compacted around the pipe. At the same
time, an additional 4-foot wide/thick layer of the select on-site sandy soils was placed outside
of the 'rock dust' layer until the pipe was completely covered with a 6-foot thick layer of
select material. Finally, on-site sandy soil was placed over the pipe until the design street
subgrade or slope face was achieved.
Based on the animal crossing design (LGC, 2015e), the bottom inside 4 feet of the corrugated
pipe was coated with a 50-mil thick bituminous material. A perforated 4-inch diameter
subdrain pipe inside a filter fabric sock was placed along the bottom of the pipe. The upper
end of the subdrain was capped, while the lower end was outletted beyond the downhill side
of the animal crossing structure. Two 2-foot tall cutoff walls were placed inside the
corrugated pipe to minimize erosion of the select material inside the pipe. Three (3) feet of
stabilized material was then placed inside the pipe for the animals to walk across.
Project No. 133023-03 Page 12 June 28, 2016
3.0 ENGINEERING GEOLOGIC SUMMARY
3.1 As-Graded Geolo2ic Conditions
The geologic or geotechnical conditions encountered during the mass grading of the site were
essentially as anticipated; however, the alluvium in the lower portions of the main tributary
canyons along the north side of El Camino Real were significantly deeper than anticipated
based on data from the project preliminary geotechnical investigations (Appendix A). In
addition, the questionable landslide previously mapped in the northeastern portion of the site
was not encountered during the mass grading operations; but was observed to consist of
formational material dipping the opposite direction than the typical bedding on the remainder of
the site. Finally, a shallow perched groundwater condition was present in the area of Planning
Area PA-2 that precluded complete removal of the saturated alluvial soils. Instead of the
complete removal of the alluvium, a stabilization fabric underlain in places with a layer of rock
was placed on top of the saturated alluvium prior to the placement of fill. A comprehensive
summary of the geologic conditions (including geologic units, geologic structure, and faulting)
is presented below.
3.2 Geoloj'ic Units
The geologic units encountered during the mass grading operations consisted of documented
and undocumented fill, topsoil, colluvium, alluvium, terrace deposits and the Santiago
Formation. Due to the potentially compressible nature of the desiccated documented fill,
undocumented fill, topsoil, colluvium, alluvium, and weathered formational material, these
soils were removed to competent material during the mass grading operations. The as-graded
geologic units encountered during the grading operations are discussed (youngest to oldest)
below. The approximate limits of the mapped geologic units is presented on the As-Graded
Geotechnical Map (Plates 1A through IF).
Documented Fill
Previous .grading of a portion of Planning Areas PA-9, PA- 11, PA-13, PA-23C, and the
widening of the north side of El Camino Real west of Cannon Road has created a number
of fill areas along the southern portion and northeast corner of the site. These fills generally
consisted of clayey to silty sands and sandy clays derived from native soils and were found
to be moderately to well compacted and damp to moist. Prior to the placement of fill in
these areas, the dry and desiccated upper ito 3 feet of the documented fill was removed to
competent material.
Undocumented Fill
Undocumented fill soils were observed in a number of places on the site. The
undocumented fills were generally associated with the grading of the onsite dirt roads,
retention basins, and prior farming activities. These fill soils ranged from less than 1 to
Project No. 133023-03 Page 13 June 28, 2016
approximately 10 feet in depth, and generally consist of dry to damp, loose or soft, sand and
sandy clay. All existing undocumented fill located within the limits of grading were
removed to competent formational material.
Topsoil
A relatively thin veneer of topsoil was removed from the higher elevations of the site. The
topsoil, as encountered, consisted predominantly of a dark brown, damp to moist, loose,
sandy clay and minor clayey to silty sand. The topsoil was generally massive, porous, and
contained scattered roots and organics. Topsoil removal thicknesses were on the order of 1
to 4 feet thick. During the grading operations, the topsoil was observed to have been
removed within the limits of grading.
Alluvium and Coiluvium
Alluvium and colluvium was encountered during the mass grading operations in the
canyons and on the lower portion of the hillsides on the site. The alluvium and colluvium
typically consisted of light brown to dark brown, damp to moist, silty fine sands, sandy
clays and clayey sands derived from the terrace deposits and the formational material and
were found to be low to highly expansive, porous, and contained scattered organics.
Removals of up to approximately 40 feet in depth (typical removals were on the order of
less than 10 to 15 feet) were made within the alluvial soils present in the main tributary
canyons in the southern portion of the site along the north side of El Camino Real within
Planning Areas PA-2, PA-3, PA-6 through PA-8, PA- 11, and PA-23A through PA-23C.
Removals of the colluvium, on the order of 2 to 6 feet, were made on the middle and
lower portions of the hillsides on the site.
Terrace Deposits
Terrace or older alluvial flood-plain deposits were encountered in the south-central and
southeastern portion of the site within Planning Areas PA-7, PA-8, PA- 11, PA-13, and PA-
23C. As encountered, these soils consisted of silty fine to medium sand, clean sands, and
sandy to silty clays with minor gravels. The nature of the contact between the terrace
deposits and formational material, where observed, was a relatively sharp contact with a
near horizontal orientation. Along the northern contact, east of PA-7, the terrace deposits
appeared to be deposited against a river bank with a moderately steep contact up to 5 to 10
feet in height.
Santiago Formation
The Tertiary-aged Santiago Formation, as encountered during the mass grading operations,
consisted primarily of massively bedded sandstones to cross-bedded silty sandstones and
generally consisted of pale gray, pale brown and pale orange brown (where iron-oxidized
stained), damp to moist, dense to very dense, silty very fine to medium grained sandstone.
Several of these sandstone beds are friable to well-cemented fossiliferous sandstone beds.
Minor beds of claystones/siltstones were present in the lower elevations of the formation
Project No. 133023-03 Page 14 June 28, 2016
and were generally olive-green to gray (unweathered) and orange brown (where oxidized),
damp to moist, stiff to hard, moderately weathered, and occasionally fractured and
moderately sheared.
3.3 Geo1oic Structure
The general structure of the formational material appears to be slightly dipping less than 15 to
20 degrees to the west/southwest. Based on our geologic mapping during the mass grading
operations, bedding within the Santiago Formation in the western portion of the site mostly
trends northwest-southeast with dips typically between 6 and 16 degrees to the southwest. In
the central portion of the site, the bedding becomes somewhat variable with most bedding
striking northwest-southeast with dips typically 2 to 18 degrees to the southwest and northeast.
However, some of the bedding in this area trends northeast-southwest with dips of 4 to 12
degrees to the southeast. In the northeastern portion of the site, geologic mapping during
grading encountered an anticline with an axis generally in a north-south direction. Bedding on
the west side of the anticline generally trended northwest-southeast dipping 5 to 15 degrees to
the southwest while bedding on the east side of the anticline largely trended northeast-
southwest dipping 5 to 15 degrees to the southeast. Locally, cross bedding was observed with
dips steeper than 20 to 25 degrees.
Geologic mapping of the terrace deposits indicated that the deposits were massive to
indistinctly bedded. Where bedding was observed, it generally trended east-west to northeast-
southwest dipping 2 to 14 degrees to the north-northwest.
Jointing on-site was observed to be very variable, but predominantly trended subparallel to the
existing slopes. Jointing dips were found to be generally moderately to steeply dipping. Jointing
was mainly encountered in the upper portion of the bedrock becoming less pronounced with
depth.
Randomly oriented shears were encountered in the Santiago Formation claystone and siltstone
units. Numerous wide, diffuse zones of shearing, as well as more well-defined zones, were
encountered in the bedrock, and are thought to be the result of regional tectonic shearing of the
relatively stiff and unyielding siltstone and claystone.
3.4 Faultinz and Seismicity
The southern California region has long been recognized as being seismically active. The
seismic activity results from a number of active faults that cross the region, all of which are
related to the San Andreas transform system, a broad zone of right lateral faults that extend
from Baja California to Cape Mendocino. The numerous faults in Southern California include
active, potentially active, and inactive faults. The definitions of fault activity terms used here
are based on those developed for the Alquist-Priolo Special Studies Zone Act of 1972 (Bryant
and Hart, 2007).
Project No. 133023-03 Page 15 June 28, 2016
Active faults are those faults that have had surface displacement within Holocene time
(approximately the last 11,000 years) and/or have been included within an Alquist-Priolo
Special Studies Zone. Faults are considered potentially active if they show evidence of surface
displacement since the beginning of Quaternary time (about two million years ago), but not
since Holocene time. Inactive faults are those that have not had surface movement since the
beginning of Quaternary time.
The site is not within a currently established Alquist-Priolo Earthquake Fault Zone for fault
rupture hazard (formerly Special Studies Zones for fault rupture hazard). Based on a review of
geologic literature, no active faults are known to occur beneath or in the general vicinity of the
project site. Accordingly, it appears that there is little probability of surface rupture due to
faulting beneath the site. There are, however, several faults located in sufficiently close
proximity that movement associated with them could cause significant ground motion at the
site.
Although active faulting is not present within the site, faults relative to the off-shore step-over
of the Rose Canyon-Newport-Inglewood fault zone to the west and uplift of the Cretaceous
sedimentary units to the south and southeast are known to exist in general vicinity of the site.
Regional active faults that occur within the San Diego area includes the off-shore Rose
Canyon-Newport Inglewood fault zone to the west, the Elsinore, San Jacinto, and San Andreas
faults to the east, and the Coronado Bank and San Diego Trough faults offshore to the
southwest. The local Rose Canyon fault zone trends north-northwest through San Diego Bay
and downtown San Diego, crosses offshore at La Jolla Cove and continues northward off the
coast of North San Diego County. The closest known active faults to the site are the Rose
Canyon fault zone located 3.7 miles (6.0 kilometers) to the west; the Coronado Bank fault zone
located 20 miles (32 kilometers) to the southwest, and the Elsinore fault zone located
approximately 21 miles(34 kilometers) to the northeast (LGC, 2014a).
3.4.1 On-Site Faulting
Geologic mapping during the mass grading operations encountered five essentially
north-south trending faults/fault zones across the site. In general, the faults/fault zones
were approximately 800 to 1000 feet apart. With the exception of the eastern-most fault
zone, all of the other faults/fault zones were encountered in the Santiago Formation and
appeared to die out toward the south. Based on our geologic analysis during the mass
grading operations and review of the applicable geotechnical reports referenced in
Appendix A, it is our professional opinion that the faults encountered on the site are not
active; and therefore are not a constraint to development. Each of the encountered
faults/fault zones is discussed below.
Fault Zone in Western PA-3: Three minor inactive faults were geologically mapped in
the back-cut of the stability fill on the south side of Lots 135 through 145 of PA-3. The
faults generally trended in a northwest-southeast to north-south direction. This fault
zone consists of two main fault strands with the western fault downside to the west
while the eastern fault is downside to the east. The western fault generally trends
Project No. 133023-03 Page 16 June 28, 2016
N15°W to N15°E dipping 80 to 88 degrees to the northeast while the eastern strand
trends N5°W to N30°W dipping 50 to 60 degrees to the northeast. The third mapped
fault is steeply dipping and appears to die out to the north and south. A couple of
marker beds are offset and minor drag folding on the beds indicates the relative
movement is right-lateral.
Fault Zone in Western PA-5 and PA-6: The next fault zone to the east consists of one
main fault and three shorter faults geologically mapped in the stability fill back-cut in
the vicinity of Lots 52 through 57 of PA-5 and Lots 170 through 177 of PA-6. All of the
faults encountered generally trended N20°W to N35°W dipping 70 to 80 degrees to the
southwest and appeared to die out to the south. The main fault had an offset of
approximately 3 feet while the other faults had minor offsets of 6-inches or less.
Fault Zone in Eastern PA-5 and PA-6: The central fault zone was encountered along the
west side of Lots 212 through 218 of PA-6, the lots to the north in PA-6 and northward
through Lots 45 and 46 of PA-S. This fault zone consisted of three minor faults with
two of them being in-echelon. The in-echelon faults generally trended NS°W to
N15°W; however, the northern strand dipped 50 to 60 degrees to the northeast while
the southern fault dipped 75 to 85 degrees to the southwest. The sense of movement of
these faults was down to the west.
Fault Zone in PA-9 and PA-10: This fault zone was encountered running in a north
south direction through the middle of PA-9 and PA-10. Two subparallel faults were
geologically mapped in the southern and middle portions of the zone while at the north
end the two faults appeared to die out and become a series of possible step-over faults.
The two main faults generally trended NYE to N16°E dipping 60 to 85 degrees to the
west. The sense of movement of the western fault was down to the east while the
eastern fault was down to the west. The possible step-over faults trended NS°W to
N35°W dipping 55 to 70 degrees to the southwest and all were down to the west. A
short discontinuous fault was also mapped to the east with the same general trend and
dip but was down to the east.
Fault Zone in PA- 13: The eastern fault zone was encountered during the grading of PA-
12 and PA-13 in the southeast portion of Robertson Ranch by GeoSoils in 2008
(GeoSoils, 2008). The fault was exposed within the western portion of the sheet-graded
pad and found to only offset Pleistocene-aged terrace deposits. The fault was observed
to be sinuous, generally trended N30°E to NSO°E, and was moderately dipping (45 to
55 degrees) mainly to the west. The fault was found to die out in the cut slope along the
northeast side of PA-13 and could not be traced through the southern portion of the
sheet-graded pad of PA-12. Based on geologic mapping and research by GeoSoils, it
was concluded by them that the fault was pre-Holocene in age and therefore not an
active fault (GeoSoils, 2008).
The approximate 30-foot wide fault zone with multiple fault splays across the zone,
previously mapped at the southeast corner of PA-6 during the preliminary geotechnical
investigation (LGC, 2014a), was very difficult to map both towards the north and south
Project No. 133023-03 Page 17 June 28, 2016
during the mass grading operations. Based on the trend of the zone and location relative
to the fault zones mapped to the northwest and northeast, this fault zone is likely a step
over feature from one zone to the other.
3.5 Ground Water
Groundwater was encountered in the alluvium during some of the previous geotechnical
investigations at an approximate elevation of 45 feet msl. However, during the mass grading
operations only perched ground water was encountered in the alluvial soils within the main
drainage on the west side of the site and Planning Area PA-2 and in the drainage southeast of
Planning Area PA-6. With the exception of Planning Area PA-2 and the west end of Robertson
Road at Tamarack Avenue, all of the alluvial soils were completely removed to competent
formational material during the mass grading operations and subdrains installed in the canyon
bottoms. Consequently, groundwater conditions should not be a constraint to development.
However, since saturated alluvium and a shallow ground water condition is present within
Planning Area PA-2, the current groundwater condition should be evaluated as part of future
site design and construction of PA-2.
It should also be noted that no groundwater or seepage conditions were observed during the
mass grading operations within the single-family residential planning areas. However,
unanticipated seepage conditions may occur after the completion of grading and establishment
of site irrigation and landscaping. If these conditions should occur, steps to mitigate the seepage
should be made on a case-by-case basis.
Based on the site-specific as-graded geotechnical conditions and our geotechnical analysis
during site grading, LGC analyzed potential ground water conditions that may have resulted in
ground water seepage and appropriate recommendations, if necessary, have been made.
Project No. 133023-03 Page 18 June 28, 2016
4.0 CONCLUSIONS
4.1 General
The mass-grading of Robertson Ranch Planning Areas PA-1 through PA-3, PA-5, PA-6, PA-
9, PA-10, PA-13, and PA-23A through PA-23C located within the City of Carlsbad,
California was performed in general accordance with the project geotechnical report (LGC,
2014a), geotechnical recommendations made during the course of grading, and the City of
Carlsbad grading requirements. It is our professional opinion that the subject site is suitable
for the intended use provided the recommendations of the applicable referenced geotechnical
reports (LGC, 2014 through 2016j) or those provided at the completion of the future fine
grading are incorporated into the design and construction; and that proper landscaping,
irrigation, and maintenance programs are implemented. The following is a summary of our
conclusions concerning the mass-grading of Planning Areas PA-1 through PA-3, PA-S, PA-
6, PA-9, PA-b, PA-i3, and PA-23A through PA-23C.
4.2 Summary of Conclusions
Mass-grading of Robertson Ranch Planning Areas PA-i through PA-3, PA-S, PA-6, PA-9,
PA-b, PA-13, and PA-23A through PA-23C is essentially complete.
Geotechnical conditions encountered during the mass-grading operation were generally
as anticipated; with the exception of saturated alluvium in the western portion of the site
(see Section 2.2 of this report) and deeper than anticipated alluvial removals in the south-
central portion (see Section 3.2[4]).
The geologic units encountered during the mass-grading of the site consisted of
undocumented fill soils, topsoil, colluvium, alluvium, terrace deposits, and the Santiago
Formation.
Unsuitable undocumented fill soils, desiccated older fill soils, topsoil, colluvium, alluvium,
and weathered terrace deposits and formational material were removed to competent
formational material within the limits of grading.
Landslides or surficial slope failures were not encountered during the grading operations.
No evidence of active faulting was encountered during the site mass-grading operations.
However, a number of minor faults and fault zones were encountered across the site.
Based on our geologic analysis, it is our professional opinion that the faults encountered
on the site are not active; and therefore, are not a constraint to development.
Minor perched ground water seepage conditions were encountered during the remedial
grading operations within the north-south trending canyon beneath Gage Drive between
PA-6 and PA- 10; but is not considered a constraint to development.
Placement of a I- to 2-foot thick rock layer and/or a Mirafi 600x stabilization fabric was
installed in areas of PA-2 and the northwest portion of Robertson Road having a shallow
ground water condition and saturated alluvium.
Project No. 133023-03 Page 19 June 28, 2016
Since saturated alluvium and a shallow ground water condition are present within
Planning Area PA-2, the current groundwater condition should be evaluated as part of the
future site design and construction of PA-2.
Stability fills were constructed to improve the gross stability of the cut slopes exposing
fractured and blocky formational material and/or adverse geologic conditions on the site.
The stability fill keys were excavated in accordance with the project geotechnical
recommendations.
Subdrains were placed in the canyon bottoms and along the heel of the stability fill keys.
The subdrains were outletted into suitable storm drain facilities or near the toe-of-slope
of the stability fill slopes.
The cut portion of the cut/fill transition conditions present within the limits of Lots 29
through 32, 48, and 54 of PA-5; Lots 63, 68, 69, 71, 72, 77, 82, 88, 100, 112, 124, 133,
and 135 through 145 of PA-3; Lots 164, 165, 169 through 171, 189, 198 through 207, and
226 through 244 of PA-6; Lots 252, 253, 266 through 269, 275, 277 through 279, 287,
294, and 295 of PA-9; and Lots 300, 301, 305 through 307, 309 through 312, 317, 318,
and 323 of PA-10 were overexcavated a minimum of 5 feet beneath the finish grade
surface and to a distance of at least 10 feet outside the planned building limits.
Overexcavation of Lots 64 through 67, 70, 73 through 76, 83 through 87, 92 through 99,
105 through 111, 115 through 123, and 127 through 132 of PA-3; Lots 180 through 182
of PA-6; Lots 254 through 264, 270 through 274, 280 through 286, 292, 293 of PA-9; and
Lots 319 through 322 of PA-10 was performed in order to mitigate potential adverse
conditions due to expansive soils. The entire portion of the cut lots were overexcavated a
minimum of 5 feet below finish pad grade and replaced with compacted fill having a
lower expansion potential.
Overexcavation of some of the cut lots was performed in order to mitigate the potential
adverse condition of well-cemented sandstone beds (or concretion layers) and very dense or
hard Santiago Formation at or near finish grade which could create difficulties during future
excavations on the lots. Lots overexcavated due to well-cemented sandstone or dense
Santiago Formation included Lots 39 through 47 and 60 of PA-5; and Lots 158 through
163, 183, 184, 212, and 213 of PA-6.
Toxaphene impacted soil present on the site was completely removed and buried within
the street right-of-ways of the site at depths greater than 12 feet below the finish surface
of the street or 2 feet below the deepest utility if the utility line was greater than 10 feet
in depth. The burial areas included a portion of West Ranch Street, Robertson Road,
Wellspring Street, and Nelson Court. Subsequent to the grading of the site in the areas of
the previously impacted soil and burial areas, 15 random post-grading soil samples were
obtained and tested for toxaphene. The test results indicated the samples did not detect
any toxaphene
During the mass-grading operations, remedial grading was performed so that the fill
differential beneath the proposed building pads was less than a 3:1 (maximum fill thickness
to the minimum fill thickness).
Fill soils were derived from on-site soils. Where tested, the fill soils within the site were
compacted at least a 90 or 93 percent relative compaction (based on ASTM Test Method
D1557) and near-optimum moisture content in accordance with the recommendations of
Project No. 133023-03 Page 20 June 28, 2016
the project geotechnical report (LGC, 2014a) and the requirements of the City of
Carlsbad. Fill soils less than 40 feet below the design finish grades were compacted to a
minimum 90 percent relative compaction while fill soils greater than 40 feet below the
design finish grades were compacted to a minimum 93 percent relative compaction. A
summary of the results of the field density tests is presented in Appendix C.
To mitigate post-construction settlement, deep fills (i.e. areas were the fill soils are
generally deeper than approximately 40 feet below the finish grade elevations of the
sheet-graded pads) were placed at a minimum relative compaction of 93 percent relative
compaction. Deep fill areas are present on Lots 192 through 194 and Gage Drive between
PA-6 and PA-b.
Due to the dense nature of the on-site soils, it is our professional opinion that the
liquefaction hazard at the site is considered low.
Representative testing of the finish grade soils on the building pads of the subject lots
indicated that: 1) Lots 25 through 59 of PA-5; Lots 61 through 67 of PA-3; and lots 172
through 188, 206 through 213, and 226 through 251 of PA-6 have a very To expansion
potential; 2) Lots 71 through 91 of PA-3; Lots 96 through 104, 106 through 110, 127
through 130, and 135 through 145 of PA-3; and Lots 158 through 171, 189 through 199,
and 214 through 225 of PA-6 have a low expansion potential; 3) Lots 13 through 23 of
PA-13; Lot 60 of PA-5; Lots 68, 69, 70, 92 through 95, 105, 111 through 126, 131
through 134, and 146 through 149 of PA-3; Lots 200 through 205 of PA-6; Lots 252
through 299 of PA-9; and Lots 300 through 326 of PA-10 have a medium expansion
potential; and 4) Lots 1 through 12 and 24 of PA-13 have a high expansion potential. The
test results are presented in Appendix B.
The potential for soluble sulfate attack on concrete in contact with the finish grade soils
of the subject lots is considered negligible to severe based on ACT Criteria (ACT 318R-08
Table 4.3.1). The soluble sulfate content test results are included in Appendix B.
Laboratory testing of representative soil samples indicated that the near surface soils are
corrosive to severely corrosive to buried metals. The laboratory test results are presented
in Appendix B.
It is our professional opinion that the slopes of the development are considered to be
grossly and surficially stable, as constructed, under normal irrigation/precipitation
patterns, provided the recommendations in the project geotechnical reports are
incorporated into the post-grading, construction, and post-construction phases of site
development.
Based on the settlement monument readings to date of the two monuments in Planning
Area PA-6 and in Gage Drive between Planning Areas PA-6 and PA- 10 (i.e. Settlement
Monuments #6 and #7), settlement of the fills has been minimal. As a result, it is our
professional opinion that the primary and secondary consolidation of deep fills is within
acceptable limits.
The installation of the animal crossing was performed in general accordance with the
project geotechnical recommendations (LGC, 2015e) and pipe manufacture's
specifications (Sheets 45 through 51 of the Robertson Ranch Grading Plans
(O'Day, 2015).
Project No. 133023-03 Page 21 June 28, 2016
5.0 RECOMMENDATIONS
5.1 Earthwork
We anticipate that future earthwork at the site will consist of site preparation, fine-grading,
utility trench excavation and backfill, retaining wall backfill, and street/driveway and parking
area pavement section preparation and compaction. We recommend that the earthwork on
site be performed in accordance with the geotechnical recommendations presented in the
project preliminary geotechnical report (LGC, 2014a), recommendations provided after the
completion of the fine-grading operations, and the City of Carlsbad grading requirements.
5.2 Site Preparation
During future grading, the areas to receive structural fill or engineered structures should be
cleared of surface obstructions, potentially compressible material (such as desiccated fill
soils or weathered formational material), and stripped of vegetation. Vegetation and debris
should be removed and properly disposed of off-site. Holes resulting from removal of buried
obstructions that extend below finish site grades should be replaced with suitable compacted
fill material. Areas to receive fill and/or other surface improvements should be scarified to a
minimum depth of 12 inches, brought to optimum moisture condition, and recompacted to at
least 90 percent relative compaction (based on ASTM Test Method D1557).
If the length of time between the completion of grading and the construction of the
development is longer than six months, we recommend that the building pads be evaluated
by the geotechnical consultant and, if needed, the finish grade soils on the building pads
should be scarified a minimum of 12 inches, moisture-conditioned to optimum moisture-
content and recompacted to a minimum 90 percent relative compaction (based on ASTM
Test Method D1557).
5.3 PA-2 Future Work
A site-specific geotechnical evaluation should be performed once site development plans are
available. Since saturated alluvium and a shallow ground water condition are present within
Planning Area PA-2, the current groundwater condition should be evaluated as part of the
future site design and construction.
5.4 Excavations
Excavations of the on-site materials may generally be accomplished with conventional heavy-
duty earthwork equipment. It is not anticipated that blasting will be required or that significant
quantities of oversized rock (i.e. rock with maximum dimensions greater than 8 inches) will be
generated during future grading. However, localized cemented zones within the cut areas may
Project No. 133023-03 Page 22 June 28, 2016
be encountered on the site that may require heavy ripping and/or removal. If oversized rock is
encountered, it should be placed in accordance with the project geotechnical recommendations
(LGC, 2014a), hauled offsite, or placed in non-structural or landscape areas.
Temporary excavations maybe cut vertically up to five feet. Excavations over five feet should
be slot-cut, shored, or cut to a 1:1 (horizontal to vertical) slope gradient. Surface water should
be diverted away from the exposed cut, and not be allowed to pond on top of the excavations.
Temporary cuts should not be left open for extended periods. Planned temporary conditions
shOuld be reviewed by the geotechnical consultant in order to reduce the potential for sidewall
failure. The geotechnical consultant may provide recommendations for controlling the length of
sidewall exposed.
5.5 Fill Placement and Compaction
The on-site soils are generally suitable for use as compacted fill provided they are free of
organic material, debris, and rock fragments larger than 8 inches in maximum dimension. We
do not recommend that high or very high expansive soils be utilized as fill for the building pads
or as retaining wall backfill.
Fill soils should be brought to 2-percent over the optimum moisture content and compacted in
uniform lifts to at least 90 percent relative compaction based on the laboratory maximum dry
density (ASTM Test Method D1557). The optimum lift thickness required to produce a
uniformly compacted fill will depend on the type and size of compaction equipment used. In
general, fill should be placed in lifts not exceeding 8 inches in compacted thickness. Placement
and compaction of fill should be performed in general accordance with current City of Carlsbad
grading ordinances, sound construction practices, and the project geotechnical
recommendations.
If import soils are to be used as fill, the soils should be: 1) essentially free from organic matter
and other deleterious substances; 2) contain no materials over 6 inches in maximum dimension;
3) have a very low to low expansion potential (i.e. an Expansion Index ranging from 0 to 50);
and 4) have a negligible sulfate content. Representative samples of the desired import source
should be given to the Geotechnical Consultant at least 48 hours (2 working days) before
importing grading begins so that its suitability can be determined and appropriate tests
performed.
5.6 Foundation Recommendations
The preliminary foundation design recommendations applicable to the construction of the
residential structures on Planning Areas PA-3, PA-S, PA-6, PA-9, PA-b, and PA-13 of
Robertson Ranch were previously provided under separate cover (LGC, 2015a through 2016d).
The previous recommendations remain appropriate for the design of the proposed structures on
the applicable subject lots.
Project No. 133023-03 Page 23 June 28, 2016
5.7 Subdrain Outlet Maintenance
The approximate location of the subdrains and subdrain outlets constructed during the mass-
grading operations are identified on the As-Graded Geotechnical Map (Plates IA
through IF). All subdrain outlets should be periodically cleared of soil cover or other
potential blockage that may have occurred since initial subdrain construction. If retaining
walls are proposed along the toe-of-slope in the location of the stability fills/subdrain outlet
locations, the existing subdrains should be tied into the retaining wall back-drain system
and/or placed into an appropriate storm drain facility.
5.8 Control of Surface Water and Draina'e
Surface drainage should be carefully taken into consideration during fine-grading, landscaping,
and building construction. Positive drainage of surface water away from structures is very
important. No water should be allowed to pond adjacent to buildings or the top of slopes.
Positive drainage may be accomplished by providing drainage away from buildings at a
gradient of at least 2 percent for a distance of at least 5 feet, and further maintained by a swale
of drainage path at a gradient of at least 1 percent. Where limited by 5-foot side yards, drainage
should be directed away from foundations for a minimum of 3 feet and into a collective swale
or pipe system. Where necessary, drainage paths may be shortened by use of area drains and
collector pipes. Eave gutters also help reduce water infiltration into the subgrade soils if the
downspouts are properly connected to appropriate outlets.
The impact of heavy irrigation or inadequate runoff gradient can create perched water
conditions, resulting in seepage or shallow groundwater conditions where previously none
existed. Maintaining adequate surface drainage and controlled irrigation will significantly
reduce the potential for nuisance-type moisture problems. To reduce differential earth
movements (such as heaving and shrinkage due to the change in moisture content of foundation
soils, which may cause distress to a structure or improvement), the moisture content of the soils
surrounding the structure should be kept as relatively constant as possible.
All area drain inlets should be maintained and kept clear of debris in order to function properly.
Rerouting of site drainage patterns and/or installation of area drains should be performed, if
necessary. A qualified civil engineer or a landscape architect should be consulted prior to
rerouting of drainage.
Project No. 133023-03 Page 24 June 28, 2016
6.0 LIMITATIONS
Our services were performed using the degree of care and skill ordinarily exercised, under similar
circumstances, by reputable engineers and geologists practicing in this or similar localities. No other
warranty, expressed or implied, is made as to the conclusions and professional advice included in this
report. The samples taken and submitted for laboratory testing, the observations made, and the in-situ
field testing performed are believed representative of the entire project; however, soil and geologic
conditions revealed by excavation may be different from our preliminary findings. If this occurs, the
changed conditions must be evaluated by the project soils engineer and geologist and design(s) adjusted
as required or alternate design(s) recommended.
This report is issued with the understanding that it is the responsibility of the owner, or of his/her
representative, to ensure that the information and recommendations contained herein are brought to
the attention of the architect and/or project engineer and incorporated into the plans, and the
necessary steps are taken to see that the contractor and/or subcontractor properly implements the
recommendations in the field. The contractor and/or subcontractor should notify the owner if they
consider any of the recommendations presented herein to be unsafe.
The findings of this report are valid as of the present date. However, changes in the conditions of a
property can and do occur with the passage of time, whether they be due to natural processes or the
works of man on this or adjacent properties.
In addition, changes in applicable or appropriate standards may occur, whether they result from
legislation or the broadening of knowledge. Accordingly, the findings of this report may be
invalidated wholly or partially by changes outside our control.
Project No. 133023-03 Page 25 June 28, 2016
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LGC Valley, Inc.
Geotechnical Consulting
AS-GRADED REPORT OF ROUGH-GRADING,
LOTS 59, 60, 216-225, 234-244, 299-301,
308-310, AND 320-324,
PLANNING AREAS PA-5, PA-6, AND PA-9&10,
ROBER TSON RANCH,
CARLSBAD TRACT NO.13-03,
CARLSBAD, CALIFORNIA
Project No. 133023-03
Dated: February 3,2016
Prepared For:
Toll Brothers
725 Town and Country Road, Suite 200
Orange, California 92868
2420 Grand Avenue, Suite F2 • Vista • CA 92081 • (760) 599.7000 • Fax (760) 599-7007
LGC Valley, Inc.
Geotechnical Consulting
February 3, 2016 Project No. 133023-03
Mr. Greg Deacon
Toll Brothers
725 Town and Country Road, Suite 500
Orange, California 92868
Subject: As-Graded Report of Rough Grading, Lots 59, 60, 216 through 225, 234 through 244, 299
through 301, 308 throng/i 310, and 320 through 324, Planning Areas PA-5, PA-6, and PA-
9&10, Robertson Ranch, caiisbad Tract No. 13-03, Carlsbad, California
In accordance with the request and authorization of Toll Brothers, LGC Valley, Inc. (LGC) has provided
geotechnical services during the rough-grading operations for Lots 59 and 60 of Planning Area PA-5; Lots 216
through 225 and 234 through 244 of Planning Area PA-6; and Lots 299 through 301, 308 through 310, and 320
through 324 of Planning Areas PA-9 and PA-10; part of the Robertson Ranch project (Carlsbad Tract No. 13-
03) located within the City of Carlsbad, California. The accompanying as-graded report of rough-grading
summarizes our observations, field and laboratory test results, and the geotechnical conditions encountered
during grading of the subject lots.
The rough-grading operations for the subject lots were performed in general accordance with previously
published project geotechnical reports (Appendix A), geotechnical recommendations made during the course of
grading, and the City of Carlsbad grading requirements. It is our professional opinion that the subject lots are
suitable for the intended use provided the recommendations included herein and in the project geotechnical
reports are incorporated into the fine-grading, design, and construction of the proposed development and
associated improvements. As of the date of this report, the rough-grading operations for the subject lots are
essentially complete.
If you have any questions regarding our report, please contact this office. We appreciate this opportunity to be
of service.
Respectfully Submitted,
LGC Valley, Inc.
0 ~ wo-~,
Randall Wagner, CEG 1612
Senior Project Geologist
~4
Basil Hattar, GE 2734
Principal Engineer
Distribution: (7) Addressee
(1) Toll Brothers; Attention Ms. JoAnn Epstine (via e-mail)
(I) Toll Brothers; Attention Mr. Kevin Brickley (via e-mail)
(1) Toll Brothers; Attention Mr. Mike Steffen (via e-mail)
2420 Grand Avenue, Suite F2 Vista • CA 92081 • (760) 599-7000 • Fax (760) 599-7007
TABLE OF CONTENTS
Section, Page
1.0 INTRODUCTION ..................................................................... . ................................................................... I
2.0 SUMMARY OF ROUGH-GRADING OPERATIONS ................................................................................. .2
2.1 As-Graded Conditions ....................................................................................................................... 2
2.2 Site Preparation and Removals . ........................................................................................................ 3
2.3 Stability Fills ............................................ ... ......... . ............................................................................ 4
2.4 Subdrain Installation ......................................................................................................................... 4
2.5 Overexcavation of Cut/Fill Transition conditions .......................4
2.6 Overexcavation of Cut Lots ........................................................... .......... . ......................................... 5
2.7 Fill Placement and Compaction........................................................................................................5
2.8 Laboratoiy Testing............................................................................................................................5
2.9 Field Density Testing ........................................................................................................................ 5
2.10 Graded Slopes ................................................................. . ... . .... . ........................................................ 6
3.0 CONCLUSIONS ........................................... ................................................................................................ 7
3.1 General ........................................................................................................................ ..................... 7
3.2 Summary of Conclusions ..................................................................................................................7
4.0 RECOMMENDATIONS ................................................ ................................... . .......................................... 9
4.1 Earthwork ........................................................... .............................................................................. 9
4.2 Site Preparation ...............................................................................................................................9
4.3 Excavations ......................................................................................................................................9
4.4 Fill Placement and Compaction ................................................................................. . ................... 10
4.5 Preliminary Foundation Recommendations ...................................................................................10
4.6 Control of Suiface Water and Drainage ........................................................................................ II
5.0 LIMITATIONS ....................................................................................... ....... .................... ........................... 12
Appendices
Appendix A - References
Appendix B - Laboratory Testing Procedures and Test Results
Project No. 133023-03 Page i February 3, 2016
1.0 INTRODUCTION
In accordance with the request and authorization of Toll Brothers, LGC Valley, Inc. (LGC) has provided
geotechnical services during the rough-grading operations of Lots 59 and 60 of Planning Area PA-5; Lots 216
through 225 and 234 through 244 of Planning Area PA-6; and Lots 299 through 301, 308 through 310, and
320 through 324 of Planning Areas PA-9 and PA-1 0,- part of the Robertson Ranch project (Carlsbad Tract No.
13-03) located within the City of Carlsbad, California. This as-graded report summarizes our observations,
field and laboratory test results, and the geotechnical conditions encountered during grading of the subject
lots. The subject rough-grading operations were performed in general accordance with previously
published project geotechnical reports (Appendix A), geotechnical recommendations made during the
course of grading, and the City of Carlsbad grading requirements. As of this date, the rough-grading
operations for the subject lots are essentially complete.
The Rough Grading Plans for the Robertson Ranch project, prepared by O'Day Consultants (O'Day, 2014b),
were utilized as a base map to present the as-graded geotechnical conditions and approximate locations of the
field density tests. The As-graded Geotechnical Map and the Field Density Test Location Map will be
provided in the final as-graded report for Robertson Ranch upon completion of all of the rough-grading
operations.
Lots 59 and 60 of Planning Area PA-5 are located in the western portion of Robertson Ranch along the south
side of Glasgow Drive while Lots 216 through 225 and 234 through 244 of Planning Area PA-6 and Lots 299
through 301, 308 through 310, and 320 through 324 of Planning Areas PA-9 and PA-10 are located in the
east-central portion of the project along Wadsworth Street, Chase Court and Keniner Court. Ultimately,
development of Planning Area PA-S, PA-6, and PA-9 and 10 will include the construction of 36, 87, and
75 single-family residential lots, respectfully; along with associated retaining walls, slopes, storm water
retention basins, and adjacent streets. The rough-grading operations for Lots 59 and 60 of Planning Area
PA-5; Lots 216 through 225 and 234 through 244 of Planning Area PA-6; and Lots 299 through 301, 308
through 310, and 320 through 324 of Planning Areas PA-9 and PA-la were performed as a part of grading
operations for the entire Robertson Ranch Development between September 2014 and October 2015.
Project No. 133023-03 Page 1 Februaiy 3, 2016
2.0 SUMMARY OFRO UGH- GRADING OPERATIONS
Rough-grading of the subject site began on September 5, 2014 and was essentially completed as of October
22, 2015. The grading operations were performed under the observation and testing services of LGC Valley,
Inc. Our field technicians were onsite on a full-time basis during the grading operations while our field
geologist was onsite on a periodic basis. The rough-grading operations included:
I) Removal and off-site disposal of vegetation and miscellaneous debris;
The removal of potentially compressible soils including colluviurn, topsoil, undocumented fill, and
weathered soils to competent formational material;
Overexcavation of cut/fill transition conditions within the lots;
Overexcavation of buried cut/fill transition conditions such that the resulting fill differential beneath
the proposed building pads was less than a 3:1 (maximum fill thickness to the minimum fill
thickness);
Overexcavation of cut lots due to expansive soils;
Preparation of areas to receive fill;
The placement of subdrains in the canyon bottoms and along the heel of the stability fill keys;
Excavation of formational material; and
The placement of compacted fill soils creating the graded pads and adjacent slopes.
The rough-grading operations consisted of the placement of fill up to approximately 45 feet in depth and
cuts up to approximately 20 feet within the subject lots. During the rough-grading operations, remedial
grading was also performed so that the fill differentials beneath the proposed building pads were less than a
3:1 (maximum fill thickness to the minimum fill thickness).
2.1 As-Graded Conditions
The as-graded conditions encountered during grading of the lots were essentially as anticipated. In the
vicinity of the Lots 234 through 244, 299, 308, 309, 323, and 324, minor alluvium and colluvium
were encountered on the upper hillsides and small tributary ravines of the main canyon running in a
northwest-southeast between Planning Areas PA-6 and PA-9/PA-10 and in the small canyon in the
vicinity of Lots 323 and 324. Formational material was encountered on the slopes and at design cut
grade below a thin veneer of topsoil and weathered soils on the remainder of the lots.
All unsuitable and potentially compressible soils were removed prior to fill placement. This included
alluvium, colluvium, undocumented fill (associated with the past agricultural operations), and
weathered formational materials. The alluvium, colluvium, and topsoil typically consisted of light
brown to brown silty fine sands, sandy clays and clayey sands derived from on-site soils and were
found to be very low to highly expansive, porous, and contained scattered organics. Removals of
alluvium and colluvium up to approximately 5 to 15 feet in depth were made in the vicinity of Lots
234 through 244, 299, 308, 309, 323, and 324. Removals of the topsoil and weathered formational
material that was on the order of 2 to 6 feet were made in the other areas of the site.
Project No. 133023-03 Page 2 Februaiy 3, 2016
The formational material encountered on the subject lots consisted of the Santiago Formation. The
material was found to be massively bedded to cross-bedded silty sandstones and minor clayey
sandstones, silty claystones and sandy siltstones The claystones and siltstones generally were olive
green and orange brown, damp to moist; stiff to hard, moderately fractured and sheared. The
sandstone generally consisted of light olive green, light brown and pale orange brown (where iron-
oxidized stained), damp to moist, dense to very dense, silty very fine to medium grained sandstone.
The majority of the Santiago material encountered within Robertson Ranch consisted of silty fine
sands. Bedding within the Santiago Formation was highly variable, but overall, generally dipped 2
to 15 degrees to the west-southwest.
A one of two to three minor inactive faults was geologically mapped trending in a: north-south
direction in the middle of Planning Areas PA-9 and PA-b. Geologic mapping indicated the faults
trended N3°E to Nl6°E steeply dipping 60 to 85 degrees to the west The faults were only observed
within the Santiago Formation and the fault zone appeared to die but to the: south. Based on our
geologic analysis during the current grading operations and review'of the applicable geotechnical
reports referenced in Appendix A, it is our professional opinion that the faults are not active; and
therefore are not a constraint to development.
No groundwater was encountered during the grading of the subject lots However, unanticipated
seepage conditions may occur after the completion of grading and establishment of site irrigation
and landscaping. If these conditions should occur, steps to mitigate the seepage should be made on
a case-by-case basis.
2.2 Site Prevaration and Removals
Prior to grading, the site was cleared of light vegetation and other miscellaneous debris and the
material was disposed of at an offsite facility. Undocumented fill, topsoil, alluvium, colluviurn, and
weathered formational material were removed down to competent material (i.e. dense unweathered
formational material). Remedial removals on site, below the existing ground surface, ranged from
approximately 2 to 20 feet in depth. The thickness of compacted fills placed during this recent rough-
grading operation, to achieve design rough grades (or sheet-graded pad elevations), ranged from 0 to
approximately 45 feet.
Following the remedial removals or overexcavations, areas to receive • fill were scarified
approximately 6-inches, moisture-conditioned, as needed, to obtain a near-optimum moisture content
and compacted to a minimum 90 percent relative compaction (for fills of approximately 40 feet or I
less from design grades) or 93 percent relative compaction (for engineered fill below approximately
40 feet from design finish grades), as determined by ASTM Test Method D6938 (i.e. the nuclear
gauge method).
Project No, 133023-03 Page 3 Februaiy 3, 2016
Z3 Stability Fills
Stability fills were constructed to stabilize theexposed blocky claystone/siltstone and/or adverse (i.e.
out-of-slope) geologic conditions present within the Santiago Formation. The stability fill keys were
excavated to a width of approximately 15 feet and a minimum depth of 3 to 5 feet below the toe-of-
slope. The keyway bottom was angled at least 2 percent into-the-slope.
The stability fill font cuts were excavated neat vertical while the back-cuts 'were excavated at an
approximate 1:1 to 1.5 (horizontal to vertical) slope inclinations. Stability fills were excavated along
the proposed slopes on: 1) the southwest side Lot 60; 2) the southeast side of Lots 59 and 60; 3) the
west side of Lots 216 through 225; 4) the north side of Lots 299 through 301; and 5) the north side of
Lots 320 through 323. .
2.4 Subdrain Installation
Canyon and stability fill subdrains were installed tinder the observation of a repiësentative of LGC in
general accordance with the planned locations of the approved geotechnical report, and the standard
details (LGC, 2014a). After the potentially compressible material in the canyons were removed to
competent material or when compacted fill was placed over competent material to obtain flow to a
suitable outlet location, a subdrain was installed along the canyon bottom.
The canyon subdrains consisted of a 6-inch diameter perforated pipe surrounded by a minimum of 9-
cubic feet (per linear foot) of crushed 3/4-inch gravel wrapped in Mirafi 140N filter fabric. In addition
to the canyon subdrains, subdrains were also installed along the bottom backside of the stability fill
keys. The stability fill subdrains consisted of a 4-inch diameter perforated pipe surrounded by a
minimum of 3-cubic feet (per linear foot) of clean 3/4-in6h gravel wrapped in Mirafi 140N filter
fabric.
The canyon and stability fill subdrains were placed with a minimum 1-percent fall (2-percent or
greater where possible) to a suitable outlet location. The location of the subdrains placed during the
mass grading operations for the project were surveyed by the project civil engineer.
2.5 Overexcavation of Cut/Fill Transition Conditions
Based on the as-graded conditions, the cut/fill transition condition present within the lots, as shown on
the rough grading plans (O'Day, 2014b), were overexcavated a minimum of 5 feet in depth beneath
the proposed finish grade surface of the lot. The overexcavation extended to a distance of at least 10
feet outside the planned building limits. Lots that were overexcavated .due to the cut/fill transition
condition include Lots 244, 300, 301, 310, 322, and 323. During the rough-grading operations;
remedial grading was also performed so that the fill differential beneath the proposed building pads
was less than a 3:1 (maximum fill thickness to the minimum fill thickness).
Project No. 133023-03 Page 4 Februaiy 3, 2016
2.6 Overexcavation of Cut Lots
During the rough-grading operations, the overexcavation of cut lots was performed in order to
mitigate potential adverse conditions due to expansive soils. The entire portion of the cut lots were
overexcavated a minimum of 5 feet below finish pad grade and replaced with compacted fill having a
lower expansion potential. In order to minimize potential ponded ground water conditions on the
overexcavation bottom, the bottom was sloped toward the street with a minimum fall of one percent.
Cut lots that were overexcavated included Lots 60, 320, and 321
2.7 Fill Placement and Compaction
After processing the areas to receive fill, native soil was generally spread in approximately 8-inch
loose lifts, moisture-conditioned as needed to attain near-optimum moisture content, and compacted
to at least 90 or 93 percent of the maximum dry density determined in accordance with ASTM Test
Method D1557. Fill soils less than 40 feet below the design finish grades were compacted to a
minimum 90 percent relative compaction while fill soils greater than 40 feet below the design finish
grades were compacted to a minimum 93 percent relative compaction. Compaction was achieved by
use of heavy-duty construction equipment. Areas of fill in which either field density tests indicated
less than 90 or 93 percent relative compaction or the soils exhibited nonuniformity and/or showed an
inadequate or excessive moisture content, were reworked, recompacted, and retested until a minimum
90 or 93 percent relative compaction and near-optimum moisture content was achieved.
2.8 Laboratory Testing
Maximum dry density tests of representative on-site soils were performed (by others during the
previous investigation and by LGC during the current rough-grading operations) in general
accordance with ASTM Test Method D1557. Expansion potential, soluble sulfate content, and
corrosion testing of representative finish grade soils within the subject lots were performed. Based on
the laboratory testing, Lots 59 and 234 through 244 have a very low expansion potential; Lots 216
through 225 have a low expansion potential; and Lots 60, 299 through 301, 308 through 310, and 320
through 324 have a medium expansion potential. Laboratory testing also indicated that the near
surface soils have a negligible soluble sulfate content; are corrosive to severely corrosive to buried
metals based on the minimum soil resistivity values; and are corrosive to buried metals and
reinforcing steel in concrete based on the chloride concentrations. The laboratory test results are
presented in Appendix B.
2.9 Field Density Testing
Field density testing was performed using the Nuclear-Gauge Method (ASTM Test Method
D6938). The approximate test locations and the results of the field density tests will be provided in
the final as-graded report for Robertson Ranch upon completion of the rough grading operations.
The field density testing was performed in general accordance with the applicable ASTM standards
' Project No. 133023-03 Page 5 February 3, 2016
and the current standard of care in the industry. In-situ soil density testing is intended to verify the
effectiveness of the earthmoving operation in general and is performed on a spot-check basis; as
such, some variations in relative compaction should be expected from the results documented
herein.
2.10 Graded Slopes
Manufactured fill slopes within the subject lots were surveyed by the civil engineer and constructed
with slope inclinations of 2:1 (horizontal to vertical) or flatter. Permanent graded fill slopes adjacent
- to or within the subject areas range from approximately 5 to 50 feet in height.. There are no
permanently graded cut slopes within or adjacent to the subject areas. Theon-site fill slopes are
considered grossly and surficially stable from a geotechnical standpoint (under normal
irrigation/precipitation patterns) provided the project geotechnical recommendations are
incorporated into the fine-grading, post-grading, construction, and post-construction phases of site
development. .
Project No. 133023-03
3.0 CONCLUSIONS
3.1 Genera!
The rough-grading of Lots 59 and 60 of Planning Area PA-5; Lots 216 through 225 and 234 through
244 of Planning Area PA 6, and Lots 299 through 301, 308 through 310, and 320 through 324 of
Planning Areas PA-9 and PA-10 of the Robertson Ranch development boated within the City of
Carlsbad, California was performed in general accordance with the project geotechnical report
(LGC, 2014a), geotechnical recommendations made during the course- of.grading, and the City of
Carlsbad grading requirements. It is our professional opinion that the subject lots are suitable for
the intended use provided the recommendations of the iefeienced geotechnical reports (LGC,
2014a and 2015a through 2016b) are incorporated into the design and construction; and that proper
landscaping, irrigation, and maintenance programs are implemented..
3.2 Summary of Conclusions
The following is a summary of our conclusions concerning the rough-grading of Lots 127 through
149 of Planning Area PA-3:
Rough-grading of the lots is essentially complete. -
Geotechnical conditions encountered during the rough-grading operation were generally as
anticipated. -
The geologic units encountered during the rough-grading of the site consisted of undocumented
fill soils, topsoil, colluvium, alluvium, and the Santiago Formation
Unsuitable undocumented fill soils, topsoil, colluvium, alluvium, and desiccated and/or weathered
formational material were removed to competent ,formational material within the limits of
grading.
Landslides or surficial slope failures were not encountered during the grading operations.
No evidence of active faulting was encountered during the rough-grading operations; however,
a zone of two to three minor inactive faults was encountered trending in north-south direction
in the middle of Planning Areas PA-9 and PA- 10 (i.e. in the vicinity Of Lots 310 and 320).
Based on our geologic analysis, it is our professional opinion that the faults are not active; and
therefore are not a constraint to development.
Ground water seepage conditions were not encountered during the subject grading operations.
Stability fills were constructed to improve the gross stability of the cut slope exposing fractured
and blocky formational material and/or adverse geologic conditions on the site and were
excavated in accordance with the project geotechnical recommendations. Stability fills were
excavated along the proposed slopes on: 1) the southwest side Lot 60; 2) the southeast side of
Lots 59 and 60, 3) the west side of Lots 216 through 225, 4) the north side of Lots 299 through
301; and 5) the north side of Lots 320 through 323. •
-
. -
Project No. 133023-03 Page 7 .. • •.February 3, 2016
-1 -
Subdrains were placed in the canyon bottom and along the heel of the stability fill keys. The
subdrains were (or will be) outletted into suitable storm drain facilities or near the toe-of-slope
of the stability fill slopes.
The cut/fill transition conditions present within the limits of Lots 244,300, 301, 310, 322, and 323
were overexcavated a minimum of 5 feet beneath the finish grade surface and to a distance of at
least 10 feet outside the planned building limits.
Overexcavation of Lots 60, 320, and 321 was pefformed in order to mitigate potential adverse
conditions due to expansive soils. The entire portion of the cut lots were overexcavated a
minimum of 5 feet below finish pad grade and replaced with compacted fill having a lower
expansion potential.
During the rough-grading operations, remedial grading was performed so that the fill differential
beneath the proposed building pads was less than a 3:1 (maximum fill thickness to the minimum
fill thickness),
Fill soils were derived from on-site soils Where tested, the fill soils within the site were
compacted at least a 90 or 93 percent relative compaction (based on ASTM Test Method
D1557) and near-optimum moisture content in accordance with the recommendations of the
project geotechnical report (LGC, 2014a) and the requirements of the City of Carlsbad. Fill
soils less than 40 feet below the design finish grades were compacted to a minimum 90 percent
relative compaction while fill soils greater than 40 feet below the design finish grades were
compacted to a minimum 93 percent relative compaction.
Due to the dense nature of the on-site soils, it is our professional opinion that the liquefaction
hazard at the site is considered low.
Representative testing of the finish grade soils on the building pads Of the subject lots indicated
that the near-surface soils on Lots 59 and 234 through 244 have a very low expansion potential;
Lots 216 through 225 have a low expansion potential; and Lots 60, 299 through 301, 308 through
310, and 320 through 324 have a medium expansion potential. The test results are presented in
Appendix B.
The potential for soluble sulfate attack on concrete in contact with the finish grade soils of the
subject lots is considered negligible based on ACT Criteria (ACl 318R-05 Table 4.3.1). The
soluble sulfate content test results are included in Appendix B.
Laboratory testing of representative soil samples indicated that the near surface soils are corrosive
to severely corrosive to buried metals. The laboratory test results are presented in Appendix B.
It is our professional opinion that the slopes of the development are considered to be grossly
and surficially stable, as constructed, under normal irrigation/precipitation patterns, provided
the recommendations in the project geotechnical reports are incorporated into the post-grading,
construction and post-construction phases of site development.
Project No. 133023-03 Page 8 Februaiy 3, 2016
4.0 RECOMMENDATIONS
4.1 Earth work
We anticipate that future earthwork at the site will consist of site preparation, fine-grading, utility
trench excavation and backfill, retaining wall backfill, and street/driveway - and parking area
pavement section preparation and compaction. We recommend that the earthwork on site be
performed in accordance with the geotechnical recommendations: presented in the project
preliminary geotechnical report (LGC, 2014a) and the City of Carlsbad grading requirements
4.2 Site Preparation
During future grading (if any), the areas to receive structural fill or engineered structures should be
cleared of surface obstructions, potentially compressible material (such as desiccated fill soils or
weathered formational material), and stripped of vegetation. Vegetation and debris should be
removed and properly disposed of off-site. Holes resulting from removal of buried obstructions that
extend below finish site grades should be replaced with suitable compacted fill material. Areas to
receive fill and/or other surface improvements should be scarified to a minimum depth of 12
inches, brought to optimum moisture condition, and recoinpacted to at least 90 percent relative
compaction (based on ASTM Test Method D1557).
If the length of time between the completion of grading and the construction of the development is
longer than six months, we recommend that the building pads be evaluated by the geotechnical
consultant and, if needed, the finish grade soils on the building pads should be scarified a minimum
of 12 inches, moisture-conditioned to optimum moisture-content and recompacted to a minimum
90 percent relative compaction (based on ASTM Test Method D1557).
4.3 Excavations
Excavations of the on-site materials may generally be accomplished with conventional heavy-duty
earthwork equipment. It is not anticipated that blasting will be required or that significant quantities of
oversized rock (i.e. rock with maximum dimensions greater than 8 inches) will be generated during
future grading. However, localized cemented zones within the cut areas may be encountered on the
site that may require heavy ripping and/or removal. If oversized rock is encountered, it should be
placed in accordance with the project geotechnical recommendations (LGC, 2014a), hauled offsite, or
placed in non-structural or landscape areas.
Temporary excavations maybe cut vertically up to five feet. Excavations over five feet should be slot-
cut, shored, or cut to a 1:1 (horizontal to vertical) slope gradient. Surface water should be diverted
away from the exposed cut, and not be allowed to pond on top of the excavations. Temporary cuts
should not be left open for an extended period of time. Planned temporary conditions should be
reviewed by the geotechnical consultant in order to reduce the potential for sidewall failure. The
geotechnical consultant may provide recommendations for controlling the length of sidewall exposed.
Project No. 133023-03 Page 9 : February 3, 2016
4.4 Fill Placement and Compaction
The on-site soils are generally suitable for use as compacted fill provided they are free or organic
material, debris, and rock fragments larger than 8 inches in maximum dimension. We do not
recommend that high or very high expansive soils be utilized as fill for the building pads or as
retaining wall backfill.
All fill soils should be brought to 2-percent over the optimum moisture content and compacted in
uniform lifts to at least 90 percent relative compaction based on the laboratory maximum dry density
(ASTM Test Method D1557). The optimum lift thickness required to produce a uniformly compacted
fill will depend on the type and size of compaction equipment used. In general, fill should be placed
in lifts not exceeding 8 inches in compacted thickness. Placement and compaction of fill should be
performed in general accordance with current City of Carlsbad grading ordinances, sound
construction practices, and the project geotechnical recommendations.
If import soils are to be used as fill, they should be: 1) essentially free from organic matter and other
deleterious substances; 2) contain no materials over 6 inches in maximum dimension; 3) have a very
low to low expansion potential (i.e. an Expansion Index ranging from 0 to 50); and 4) have a
negligible sulfate content. Representative samples of the desired import source should be given to the
Geotechnical Consultant at least 48 hours (2 working days) before importing grading begins so that its
suitability can be determined and appropriate tests performed,
4.5 Foundation Recommendations
The preliminary foundation design recommendations applicable to the construction of the residential
structures on the subject lots were previously provided in the our letter report entitled 'Preliminary
Foundation Design for the Single-Family Residential Structures, Planning Areas .PA-3, PA-5, PA-6,
PA-9, PA-b, and PA-13, Robertson Ranch", dated April 14, 2015 (LGC, 2015a) and our letter
entitled "Deepened Footing Recommendation of Building Foundation Adjacent to Proposed Nexus
eWater Recycler System, Planning Areas PA-3, PA-5, PA-6, PA-9, PA-10, and PA-13, Robertson
Ranch" dated July 23, 2015 (LGC, 2015c). The previous recommendations remain applicable for the
design of the proposed structures on the subject lots.
Based on the expansion potential and corrosion laboratory testing of representative soils on the
subject lots, Lots 59 and 234 through 244 have a very low expansion potential; Lots 216 through 225
have a low expansion potential; and Lots 60, 299 through 301, 308 through 310, and 320 through 324
have a medium expansion potential. The finish grade soils on these lots are considered to have
negligible sulfate content and are corrosive to severely corrosive to buried metals. The results of the
expansion potential and corrosion testing are presented in Appendix B.
Project No. 133023-03 Page 10 February 3, 2016
4.6 Control of Surface Water and Drainage
Surface drainage should be carefully taken into consideration during fine-grading, landscaping, and
building construction. Positive drainage of surface water away from structures is very important. No
water should be allowed to pond adjacent to buildings or the top of slopes. Positive drainage may be
accomplished by providing drainage away from buildings at a gradient of at least 2 percent for a
distance of at least 5 feet, and further maintained by a swale of drainage path at a gradient of at least I
percent. Where limited by 5-foot side yards, drainage should be directed away from foundations for a
minimum of 3 feet and into a collective swale or pipe system. Where necessary, drainage paths may
be shortened by use of area drains and collector pipes. Eave gutters also help reduce water infiltration
into the subgrade soils if the downspouts are properly connected to appropriate outlets.
The impact of heavy irrigation or inadequate runoff gradient can create perched water conditions,
resulting in seepage or shallow groundwater conditions where previously none existed. Maintaining
adequate surface drainage and controlled irrigation will significantly reduce the potential for
nuisance-type moisture problems. To reduce differential earth movements (such as heaving and
shrinkage due to the change in moisture content of foundation soils, which may cause distress to a
structure or improvement), the moisture content of the soils surrounding the structure should be kept
as relatively constant as possible.
All area drain inlets should be maintained and kept clear of debris in order to function properly.
Rerouting of site drainage patterns and/or installation of area drains should be performed, if necessary.
A qualified civil engineer or a landscape architect should be consulted prior to rerouting of drainage.
Project No. 133023-03 Page 11 February 3, 2016
5.0 LIMITATIONS
Our services were performed using the degree of care and skill ordinarily exercised, under similar
circumstances, by reputable engineers and geologists practicing in this or similar localities No other warranty,
expressed or implied, is made as to the conclusions and professional advice included in this report. The
samples taken and submitted for laboratory testing, the observations made and the in-situ field testing
performed are believed representative of the entire project; however, soil and geologic conditions revealed by
excavation may be different than our preliminary findings. If this occurs, the changed conditions must be
evaluated by the project soils engineer and geologist and design(s) adjusted as required or alternate design(s)
recommended.
This report is issued with the understanding that it is the responsibility of the owner, or of his/her
representative, to ensure that the information and recommendations contained herein are brought to the
attention of the architect and/or project engineer and incorporated into the plans, and the necessary steps
are taken to see that the contractor and/or subcontractor properly implements the recommendations in the
field. The contractor and/or subcontractor should notify the owner if they consider any of the
recommendations presented herein to be unsafe.
The findings of this report are valid as of the present date. However, changes in the conditions of a
property can and do occur with the passage of time, whether they be due to natural processes or the works
of man on this or adjacent properties.
In addition, changes in applicable or appropriate standards may occur, whether they result from legislation
or the broadening of knowledge. Accordingly, the findings of this report may be invalidated wholly or
partially by changes outside our control.
Project No, 133023-03 Page 12 February 3, 2016
APPENDIXA.
References
American Society of Civil Engineers (ASCE), 2013, Minimum design loads for buildings and other
structures, ASCE/SEI 7-10, Third Printing, 2013.
California Building Standards Commission (CBSC), 2013a, California Building Code, California
Code of Regulations, Title 24, Part 2, Volume I and 2 of 2 (based on the 2012 International
Building Code).
CBSC, 2013b, California Residential Building Code, California Code of Regulations, Title 24, Part
2.5,(based on the 2012 International Residential Code).
CBSC, 2013c, California Green Building Standards Code, California Code of Regulations, Title 24,
Part 11.
GeoSoils, Inc., 2002, Geotechnical evaluation of the Robertson Ranch Property, City of Carlsbad,
San Diego County, California, W.O. 3098-Al-SC, dated January 29, 2002.
GeoSoils, Inc., 2004, Updated geotechnical evaluation of the Robertson Ranch property, Carlsbad,
San Diego County, California, W.O. 3098-A27SC, dated September 20, 2004,
GeoSoils, Inc., 201.0, Updated geotechnical investigation for Robertson Ranch West Village,
Carlsbad, San Diego County, California, W.O. 6145-A-SC, dated October 10, 2010.
GeoSoils, Inc., 2011, Supplement to the updated geotechnical investigation for Rancho Costera
(formerly Robertson Ranch West Village), Carlsbad, San Diego County, California, W.O.
6145-Al-SC, dated June 6.
GeoSoils, Inc., 2012, Preliminary geotechnical review of "vesting master tentative map for Rancho
Costera," 40-scale plans, sheets 1 through 21, Job No. 101307, Revised May 1, 2012, by
O'Day Consultants, W.O. 6145-A9-SC, dated May 24, 2012.
GeoSoils, Inc., 2013, Addendum to the updated and supplemental geotechnical investigations for
Rancho Costera (formerly Robertson Ranch West Village), Carlsbad, San Diego County,
California, W.O. 6145-AIO-SC, dated July 16, 2013.
LGC Valley, Inc., 2014a, Geotechnical and environmental recommendations for Robertson Ranch
West, Carlsbad Tract No. 13-03, Carlsbad, California, Project Number 133023-03, dated
April 29, 2014.
LGC Valley, Inc., 2014b, Change of geotechnical consultant, Robertson Ranch West Project,
Carlsbad Tract No. 13-0, Carlsbad, California, Project No. 133023-03, dated May 6, 2014.
LGC Valley, Inc., 2015a, Preliminary foundation design for the single-family residential structures,
Planning Areas PA-3, PA-5, PA-6, PA-9, PA-b, and PA-13, Robertson Ranch, Carlsbad
Tract No. 13-03, Carlsbad, California, Project No. 1.33023-06, dated April 14, 2015.
Project No. 133023-03 Page A-i February 3, 2016
References (continued
LGC Valley, Inc., 2015b, Preliminary Review of Building Setbacks for the Proposed Residential
Planning Areas 3,5,6,9, 10, and 13, Robertson Ranch, Carlsbad Tract No. 13-03, Carlsbad,
California, Project No. 133023-03, dated February 27, 2015, revised June 24, 2015.
LGC Valley, Inc., 2015c, Deepened Footing Recommendation of Building Foundation Adjacent to
Proposed Nexus eWater Recycler System, Planning Areas PA-3, PA-5, PA-6, PA-9, PA- 10,
and PA-13, Robertson Ranch, Carlsbad Tract No. 13-03, Carlsbad, California, Project No.
133023-03, dated July 23, 2015.
LGC Valley, Inc., 2015d, Geotechnical Post-Tension Foundation Plan Review for The Vistas
Development within Planning Area 6 (PA-6), Robertson Ranch, Carlsbad Tract No. 13-03,
Carlsbad, California, Project No. 133023-06, dated August 4, 2015.
LGC Valley, Inc., 2015e, Geotechnical Post-Tension Foundation Plan Review for The Vistas
Development within Planning Area 6 (PA-6), Robertson Ranch, Carlsbad Tract No. 13-03,
Carlsbad, California, Project No. 133023-06, dated October 21, 2015.
LGC Valley, Inc., 2015f, Geotechnical Post-Tension Foundation Plan Review for The Terraces
Development within Planning Areas 9 and 10 (PA-9 and PA- i 0), Robertson Ranch, Carlsbad
Tract No. 13-03, Carlsbad, California, Project No. 133023-06, dated November 23, 2015.
LGC Valley, Inc., 2015g, Presaturation Recommendations Concerning the Proposed Single-Family
Residential Structures of The Vistas Development, Lots 1 through 23 of Planning Area PA-
13 and Lots 158 through 244 of Planning Area PA-6, Robertson Ranch, Carlsbad Tract No.
13-03, Carlsbad, California, Project No. 133023-06, dated December 2, 2015.
LGC Valley, Inc., 2015h, Presaturation Recommendations Concerning the Proposed Single-Family
Residential Structures, The Bluffs, Lots 25 through 60 of Planning Area PA-5, Robertson
Ranch, Carlsbad Tract No. 13-03, Carlsbad, California, Project No. 133023-06, dated
December 9, 2015.
LGC Valley, Inc., 2015i, Presaturation Recommendations Concerning the Proposed Single-Family
Residential Structures, The Terraces, Lots 252 through 326 of Planning Areas PA-9 and PA-
10, Robertson Ranch, Carlsbad Tract No. 13-03, Carlsbad, California, Project No. 133023-
06, dated December 9, 2015.
LGC Valley, Inc., 2015j, Geotechnical Post-Tension Foundation Plan Review for The Bluffs
Development within Planning Area 5 (PA-5), Robertson Ranch, Carlsbad Tract No. 13-03,
Carlsbad, California, Project No. 133023-06, dated December 22, 2015.
LGC Valley, Inc., 2016a, Updated Corrosivity Results, Planning Areas PA-5, PA-9, and PA-b,
Robertson Ranch, Carlsbad Tract No. 13-03, Carlsbad, California, Project No. 133023-09,
dated January 27, 2016,
LGC Valley, Inc., 2016b, Geotechnical Post-Tension Foundation Plan Review for The Terraces
Development within Planning Areas 9 and 10 (PA-9 and PA-b), Robertson Ranch, Carlsbad
Tract No. 13-03, Carlsbad, California, Project No. 133023-11, dated February 1, 2016.
Project No. 133023-03 Page A-2 February 3, 2016
References (continued
Nexus eWater, 2015, Recycler System Standard Drawings, 9 Sheets, dated April 30, 2015.
O'Day Consultants, 2014a, Vesting tentative map for Carlsbad Tract No. 1303-2, 23 Sheets, dated
January 16, 2014.
O'Day Consultants, 2014b, Grading plans for Rancho Costera, Robertson Ranch West Village,
Carlsbad Tract No. 13-03, Drawing No. 480-3A, 44 Sheets, dated August 25, 2014.
Post-Tensioning Institute, 2006, Design of post tensioned slabs-on-ground, Third Addition,
Addendum I dated May 2007, and Addendum 2 dated May 2008, with errata February 4, 2010.
Specialty Steel, 2015, Post-Tension Plans, Details, and General Notes for The Bluffs (PA-5) at
Robertson Ranch, Carlsbad, California, Reference No. 4302, dated December 17, 2015.
Specialty Steel, 2016, Post-Tension Plans, Details, and General Notes for The Terraces at Robertson
Ranch, PA-9 and PA-10, Carlsbad, California, Reference No. 4301, dated November 20, 2015
with Delta I Dated January 29, 2016,
Suncoast Post-Tension, 2015, Post-Tension Plans, Details, and General Notes for The Vistas at
Robertson Ranch, PA-6, Carlsbad, California. Project No. 15-6428, dated August 3, 2015 Delta
1 dated October 8, 2015.
United States Geological Survey (USGS), 2008a, "2008 National Seismic Hazard Maps - Fault
Parameters" retrieved from:
http://geobazards.usgs.gov/cfusion/hazfaults_searcli/hf_search_rnain .cfm
USGS, 2008b, "2008 Interactive Deaggregations (Beta)," retrieved from:
https:Hgeohazards.usgs.gov/deaggint/2008/
USGS, 2013, U.S. Seismic Design Maps, retrieved from:
http://geohazards.tisgs.gov/designmaps/us/batcli.php#csv
Project No. 133023-03 Page A-3 February 3, 2016
A PPENDIX B
Laboratory Testink Procedures and Test Results
Expansion Index Tests: The expansion potential of selected materials was evaluated by the Expansion
Index Test, U.B.C. Standard No. 18-1-B. Specimens are molded under a given compactive energy to
approximately the optimum moisture content and approximately 50 percent saturation or approximately
90 percent relative compaction. The prepared 1-inch thick by 4-inch diameter specimens are loaded to
an equivalent 144 psf surcharge and are inundated with tap water until volumetric equilibrium is
reached. The results of these tests are presented in the table below:
Test Representative Lots Sample Description Expansion 1 Expansion
Location Index Potential
Lot 55 Lots 55-59 Pale brown fine SAND ii Very Low
Lot 60 Lots 60 & 68-70 Medium brown silty to clayey 70 Medium SAND
Lot 221 Lots 214-225 Pale orange brown silty fine 34 Low SAND
Lot 240 Lots 234-244 Pale gray brown silty fine SAND 10 Very Low
Lot 302 Lots 299-3 07 Olive green sandy CLAY/clayey 89. Medium SAND
Lot 309 Lots 308-316 Pale olive green silty to clayey 86 Medium SAND
Lot 321 Lots 3 17-326 Medium olive brown clayey fine 76 Medium SAND
Project No. 133023-03 Page B-i Februaiy 3, 2016
Laboratory Testing Procedures and Test Results (continued)
Soluble Sulfates: The soluble sulfate contents of selected samples were determined by standard
geochemical methods (Caltrans 417). The test results are presented in the table below:
Test Sulfate Content Potential Degree Sample Description of Sulfate Location (% by Weight) Attack*
PA-5 Pale gray silty fine SAND 0.016 Negligible
PA-5 Light grayish brown silty fine SAND 0.033 Negligible
PA-6 Medium brown silty clayey SAND 0.025 Negligible
PA-9 Pale yellow brown clayey SAND 0,071 Negligible
PA-10 Olive green silty to sandy CLAY 0.056 Negligible
* Per ACI 318R-08 Table 4.3.1.
Chloride Content: Chloride content was tested in accordance with Caltrans Test Method (CTM)
422. The results are presented below:
Test
Location Sample Description Chloride Content
(ppm)
Potential Degree of
Chloride Attack*
PA-5 Pale gray silty fine SAND 110 Negligible
PA-5 Light grayish brown silty fine SAND 220 Negligible
PA-6 Medium brown silty clayey SAND 205 Negligible
PA-9 Pale yellow brown clayey SAND 175 Negligible
PA-10 Olive green silty to sandy CLAY 230 Negligible
* Extrapolation from California Test Method 532, Method for Estimating the Time
to Corrosion of Reinforced Concrete Substructures and previous experience
Project No, 133023-03 Page B-2 Februa,y 3, 2016
Laboratory Testiiz. Procedures and Test Results (continue(l)
Minimum Resistivity and p11 Tests: Minimum resistivity and pH tests were performed in general
accordance with CTM 643 and standard geochemical methods. The electrical resistivity of a soil is a
measure of its resistance to the flow of electrical current. As results of soil's resistivity decreases
corrosivity increases. The results are presented in the table below:
Minimum Potential Degree Test Sample Description Resistivity of Corrosivity* Location (ohms-cm)
PA-5 Pale gray silty fine SAND 1500 Corrosive
PA-5 Light grayish brown silty fine SAND 570 Severely
Corrosive
Severely PA-6 Medium brown silty clayey SAND 640 Corrosive
PA-9 Pale yellow brown clayey SAND 800 Severely
Corrosive
PA- 10 Olive green silty to sandy CLAY 360 Severely
Corrosive
* NACE Corrosion Basics
Project No. 133023-03 Page B-3 February 3, 2016
LGC Valley, Inc.
Geotechnical Consulting
January 27, 2016
Mr. Mike Steffen
Toll Brothers
725 Town and Country Road, Suite 500
Orange, California 92868
Project No. 133023-09&-11
Subject: Updated C'orrosivity Results, Planning Areas PA-5, PA-9, and PA-JO, Robertson Ranch,
Carlsbad Tract No. 13-03, Carlsbad, California
Reference: LGC Valley, Inc. 2015, Prelinzinaiy Foundation Design for the Single-
Family Residential Structures, Planning Areas PA-3, PA-5, PA-6, PA-9, PA-
10, and PA-13, Robertson Ranch, Carlsbad Tract No. 13-03, Carlsbad,
Caljfbrnia, Project No. 133023-06, dated April 14, 2015
In accordance with your request, LGC Valley, Inc., (LGC) has prepared this letter to update the corrosivity
results of the finish grade soils on Planning Areas PA-5, PA-9, and PA-10 of the Robertson Ranch project
located in the City of Carlsbad, California. Preliminary corrosivity results and recommendations were
presented in our letter dated April 14, 2015 (referenced above). Upon completion of the site rough- and fine-
grading operations of Lots 25 through 60 of PA-5 and Lots 252 through 326 of PA-9 and PA-10
confirmatory sampling and testing. of representative finish grade soil samples was performed. The test results
are presented on Table 1.
Table 1
Corrosion Test Results
Sulfate Chloride Minimum Sample Sample Description Content Content pH Resistivity Location (%/ppm) (ppm) (ohms-cm)
PA-5 Pate gray silty fine SAND 0.016 110 8.32 1,500 Lot 38
PA-5 Light grayish brown silty fine SAND 0.033 220 7.58 570 Lot 60
PA-9 Pale yellow brown clayey SAND 0.071 175 5.23 800 Lot 271
PA-10 Olive green silty to sandy CLAY 0.056 230 7.45 360 Lot 302
2420 Grand Avenue, Suite F2 • Vista • CA 92081 . (760) 599-7000 • Fax (760) 599-7007
The National Association of Corrosion Engineers (NACE) defines corrosion as "a deterioration of a
substance or its properties because of a reaction with its environment." From a geotechnical viewpoint, the
"environment" is the prevailing foundation soils and the "substances" are the reinforced concrete foundations
or various buried metallic elements such as rebar, piles, pipes, etc., which are in direct contact with or within
close vicinity of the foundation soil.
In general, soil environments that are detrimental to concrete have high concentrations of soluble sulfates
and/or pH values of less than 5.5. ACT Criteria (ACT 318R-08 Table 4.3.1), provides specific guidelines for
the concrete mix design when the soluble sulfate content of the soils exceeds 0.1 percent by weight or 1,000
ppm. The minimum amount of chloride ions in the soil environment that are corrosive to steel, either in the
form of reinforcement protected by concrete cover, or plain steel substructures such as steel pipes or piles, is
500 ppm per California Test 532.
Based on the finish grade soil testing within Planning Areas PA-5, PA-9, and PA-b, the on-site soils are
classified as having a negligible sulfate exposure condition in accordance with ACI 318R-08 Table 4.3.1.
Concrete in contact with on-site soils should be designed in accordance with ACI 318R-08 Table 4.3.1 for the
negligible category. It is also our opinion that the on-site soils should be considered corrosive to severely
corrosive to buried metals in contact with the on-site soils based on the low soil resistivity values. It should
be noted that LGC is not a corrosion consultant and does not provide recommendations related to corrosion.
If needed, consultation with a competent corrosion engineer can be initiated, as necessary, to evaluate the
actual corrosion potential of the site and to provide recommendations to reduce the corrosion potential with
respect to the proposed improvements.
If you should have any questions, please do not hesitate to contact us. The undersigned can be reached at
(661) 702-8474.
Respectftmlly submitted,
LGC Valley, Inc.
Owo,~,
Randall Wagner, CEG 1612
Senior Project Geologist
?
Basil Hattar, GE 2734
Principal Engineer
Distribution: (1) Addressee
(1) Mr. Greg Deacon, Toll Brothers
Project No. 133023-09&11 Page 2 January 27, 2016
LGC Valley, Inc.
Geotechnical Consulting
April 14, 2015 ProjectNo. 133023-06
Mr. Greg Deacon
Toll Brothers
725 Town and Country Road, Suite 500
Orange, California 92868
Subject: Preliminary Foundation Design for the Single-Family Residential Structures, Planning
Areas PA-3, PA-5, PA-6, PA-9, PA-b, and PA-13, Robertson Ranch, Carlsbad Tract No.
13-03, Carlsbad, California
Introduction
In accordance with your request, LGC Valley, Inc., (LGC) has prepared this letter to provide preliminary
foundation design and updated seismic design parameters for the future development of Planning Areas PA-
3, PA-5, PA-6, PA-9, PA-b, and PA-13 of the Robertson Ranch project located in the City of Carlsbad,
California. The purpose of this letter is to provide preliminary foundation design and update seismic
parameters to be in accordance with the latest adopted building code (i.e. 2013 California Building Code,
which is based on the 2012 International Building Code). The recommendations contained herein should be
verified by LGC at the completion of grading to confirm the interpretations used herein.
Preliminary Foundation Design
The following preliminary foundation designs are provided for your review and use and are based on the site
conditions as currently understood and interpreted by LGC, and are in accordance, with the latest building code
requirements (2013 California Building Code).
General Foundation Recommendation
Preliminary recommendations for foundation design and foundation construction are presented herein. When
the structural loads for the proposed structures are known they should be provided to our office to verify the
recommendations presented herein.
The following foundation recommendations are provided. The foundations recommended for the proposed
structures are: (1) post-tension foundations; or (2) mat slabs.
For preliminary design purposes, based on the anticipated site geotechnical conditions after mass/rough
grading, the site is considered suitable for the support of the anticipated structures using a post-tensioned, or
mat slab-on-grade foundation system for the anticipated very low to high expansion potential (i.e.a 0 to 130
Expansion Index).
2420 Grand Avenue, Suite F2 • Vista • CA 92081 • (760) 599-7000 Fax (760) 599-7007
The information and recommendations presented in this section are not meant to supersede design by the
project structural engineer or civil engineer specializing in the structural design nor impede those
recommendations by a corrosion consultant. Should conflict arise, modifications to the foundation design
provided herein can be provided.
Bearins' Canacit
Shallow foundations may be designed for a maximum allowable bearing capacity of 2,000 lb/ft2 (gross), for
continuous footings a minimum of 12 inches wide and 18 inches deep, and spread footings 24 inches wide
and 18 inches deep, into certified compacted fill or bedrock. A factor of safety greater than 3 was used in
evaluating the above bearing capacity value. This value maybe increased by 250 psf for each additional foot
in depth and 100 psf for each additional foot of width to a maximum value of 3,000 psf.
Lateral forces on footings may be resisted by passive earth resistance and friction at the bottom of the
footing. Foundations may be designed for a coefficient of friction of 0,35, and a passive earth pressure of
250 lb/ft21ft. The passive earth pressure incorporates a factor of safety of greater than 1.5.
All footing excavations should be cut square and level as much as possible, and should be free of sloughed
materials including sand, rocks and gravel, and trash debris. Subgrade soils should be pre-moistened for the
assumed vey low to high expansion potential (to be confirmed at the end of grading). These allowable bearing
pressures are applicable for level (ground slope equal to or flatter than 511: IV) conditions only.
Bearing values indicated above are for total dead loads and frequently applied live loads. The above vertical
bearing may be increased by one-third for short durations of loading which will include the effect of wind or
seismic forces.
Post-Tension Foundations
Based on the site geotechnical conditions and provided the previous remedial recommendations have been
implemented during site grading, the site may be considered suitable for the support of the anticipated
structures using a post-tensioned slab-on-grade foundation system, for the anticipated very low to high
expansive soils. Based on our professional experience during the rough grading operations and limited
expansion potential testing, we anticipate that the finish grade soils within Planning Areas PA-3, PA-5, and PA-
6 will have expansion potentials ranging from very low to medium while Planning Areas PA-9, PA-10 and PA-
13 will have expansion potentials ranging from medium to high. The following section summaries our
recommendations for the foundation system.
The following table contains the geotechnical recommendations for the construction of PT slab on grade
foundations. The structural engineer should design the foundation system based on these parameters
including the foundation settlement as indicated in the following section to the allowable deflection criteria
determined by the structural engineer/architect.
Project No. 133023-06 Page 2 April 14, 2015
Preliminary Geotechnical Parameters for Post-Tensioned Foundation Design
Parameter
[
Value
Expansion Classification (Assumed to be Very Low to Low, Medium, and for High Expansion
confirmed at the completion of grading):
Thornthwaite Moisture Index (From -20
Figure 3.3):
Constant Soil Suction (From Figure 3.4): PF 3.6
PA3, PA-5, PA-3, PA-5, PA-6, PA-9, PA-10, and Anticipated Planning Areas (PA): and PA-6 PA-9, PA-b, and PA- 13 PA- 13
Center Lift Very Low to Medium Edge moisture variation distance Low (from Figure 3.6), em: — 9.0 feet 9.0 feet
Center lift, ym: 9.0 feet 0.5 inches 0.7 inches
0.3 inches
Edge Lift Very Low to Medium High
Edge moisture variation distance Low 5.0 feet 4.9 feet (from Figure 3.6), em:
Edge lift, y1 : 5.2 feet 1.1 inches 1.6 inches
0.7 inches
Soluble Sulfate Content for Design of
Concrete Mix in Contact with Site Soils in Negligible Exposure
Accordance with American Concrete (Based on preliminary testing - needs to be confirmed at the
Institute standard 318, Section 4.3: completion of grading)
Corrosivity of Earth Materials to Ferrous
Metals:
Moderately to Severely Corrosive
Modulus of Subgrade Reaction, k
(assuming presaturation as indicated 100 pci (very low to low)
below): 85 pci (medium to high)
Additional Recommendations:
Presaturate slab subgrade to at least optimum-moisture content, 1.2 times optimum moisture, or to
1.3 times optimum moisture to minimum depths of 12, 18, and 24 inches below ground surface,
respectively for very low to low, medium, and high expansion potentials.
Install a 15-mil moisture/vapor barrier in direct contact with the concrete (unless superseded by the
Structural/Post-tension engineer*) with minimum 1 inches of sand below the moisture/vapor barrier.
Minimum perimeter foundation embedment below finish grade for moisture cut off should be 12, 18,
and 24 inches, respectively for very low to low, medium, and high expansion potentials.
Minimum slab thickness should be 5 inches.
Project No. 133023-06 Page 3 April 14, 2015
The above sand and moisture/vapor barrier recommendations are traditionally included with geotechnical
foundation recommendations although they are generally not a major factor influencing the geotechnical
performance of the foundation. The sand and moisture/vapor barrier requirements are the purview of the
foundation engineer/corrosion engineer (in accordance with ACT Publication 302 "Guide for Concrete
Floor and Slab Construction") and the homebuilder to ensure that the concrete cures more evenly than it
would otherwise, is protected from corrosive environments, and moisture penetration of through the floor
is acceptable to future homeowners. Therefore, the recommendations provided herein may be superseded
by the requirements of the previously mentioned parties.
The underslab vapor/moisture retarder (i.e. an equivalent capillary break method) may consist of a minimum
15-mil thick moisture/vapor barrier in conformance with ASTM E 1745 Class A material, placed in general
conformance with ASTM E1643, underlain by a minimum 1-inch of sand, as needed. The sand layer
requirements above the vapor barrier are the purview of the foundation engineer/structural engineer, and
should be provided in accordance with ACI Publication 302 "Guide for Concrete Floor and Slab
Construction". These recommendations must be confirmed (and/or altered) by the foundation engineer, based
upon the performance expectations of the foundation. Ultimately, the design of the moisture retarder system
and recommendations for concrete placement and concrete mix design, which will address bleeding,
shrinkage, and curling are the purview of the foundation engineer, in consideration of the project
requirements provided by the architect and developer. The understab vapor/moisture retarder described
above is considered a suitable alternative in accordance with the Capillary Break Section 4.505.2.1 of the
CALGreen code.
Mat Foundations
A mat foundation can be used for support of proposed residential buildings. An allowable soil bearing
pressure of 1,000 psf may be used for the design of the mat at the surface under the slab area. The allowable
bearing value is for total dead loads and frequently applied live loads and may be increased by one-third for
short durations of loading which will include the effect of wind or seismic forces. A coefficient of vertical
subgrade reaction, k, of 85 pounds per cubic inch (pci) may be used to evaluate the pressure distribution
beneath the mat foundation. The magnitude of total and differential settlements of the mat foundation will be
a function of the structural design and stiffness of the mat.
Resistance to lateral loads can be provided by friction acting at the base of foundations and by passive earth
pressure. Foundations may be designed for a coefficient of friction of 0.35. Minimum perimeter footing
embedment provided in the previous sections maybe reduced for the mat slab design.
Coordination with the structural engineer will be required in order to ensure structural loads are adequately
distributed throughout the mat foundation to avoid localized stress concentrations resulting in potential
settlement. The foundation plan should be reviewed by LGC to confirm preliminary estimated total and
differential static settlements.
Project No. 133023-06 Page 4 April 14, 2015
Foundation Settlement
Based on the site design relative to native grades and the site remedial removals currently being performed
during site rough grading to remove all unsuitable potentially compressible soils underlying the site, fill at
the site will range from approximately 5 to 55 feet in thickness with the majority of the fill thicknesses on the
order of 5 to 30 feet in depth. The deepest fills located in the middle of the site along the north-south trending
canyon and along the sides of the open space separating Planning Areas PA-6 from Planning Areas PA-9 and
PA-b. It is anticipated that most of the consolidation will be complete by the time final design grades are
achieved due to the sandy nature of site soils.
Settlement monuments will be placed in deeper fill areas (fills greater than 40 feet in thickness) at the
completion of the grading activities, to monitor the primary and secondary consolidation of deep fills.
Deeper fill lots will be released when the primary and secondary consolidation is within acceptable limits.
Based on a preliminary review of site grading plans major fill differentials are not anticipated across building
pad areas. Once site development plans are finalized the anticipated fill thickness and differentials on a lot by
lot basis can be determined and considered in future foundation designs.
Based on our evaluation, the static post-construction settlements for the lots with less than 40 feet of fill, and
deeper fill lots after they are released for construction is estimated to be up to a maximum differential
settlement of approximately 1-inch in 40 feet.
Foundation Setback -Top of Slope
Building foundations located close to the top of descending slopes should have a minimum setback per
Figure 1808.7.1 of the 2013 CBC. Figure 1808.7.1 of the 2013 CBC shows that the setback distance from the
bottom edge of the building foundation to the slope surface is equal to the height of slope divided by 3 up to
a maximum setback of 40 feet. The setback distances should be measured from competent materials on the
outer slope face, excluding any weathered and loose materials. If the proposed buildings are designed within
the CBC setback, the building foundations will need to be deepened to achieve the 2013 CBC building
setbacks. Once final building plot plans are finalized and based on the actual as-graded conditions, a site
specific letter can be provided to indicate the building setbacks and which lots will need deepened footings,
and the required depth of footings.
Toe of Slope Condition - Building Clearance
Section 1808.7.1 of the 2013 California Building Code (CBC) provides recommendations/discussion with
regards to the building clearance from ascending slopes. The intent of this section of the code is that the
proposed building structure below slopes shall be set a sufficient distance from the slope to provide
protection from slope drainage, erosion, and shallow failures. The code clearance for building foundations
below slopes is equal to the smaller of the height of slope divided by 2 o 15 feet. CBC Section 1808.7.5
permits an alternate clearance subject to the approval of the building official provided a geotechnical
evaluation is performed to demonstrate that the intent of Section 1808.7 would be satisfied. LGC can review
the site plans once available to evaluate the proposed building clearances.
Project No. 133023-06 Page 5 April 14, 2015
Updated Seismic Design Criteria
The site seismic characteristics were evaluated per the guidelines set forth in Chapter 16, Section 1613 of the
2013 California Building Code (CBC). The maximum considered earthquake (MCE) spectral response
accelerations (SMS and SMI) and adjusted design spectral response acceleration parameters (SDS and SDI) for
Site Class D are provided in the following table.
Seismic Design Parameters
Selected Parameters from 2013 CBC, Section 1613 - Earthquake Loads Seismic
Design Values
Site Class per Chapter 20 of ASCE 7 D
Risk-Targeted Spectral Acceleration for Short Periods (Ss)* 1.083g
Risk-Targeted Spectral Accelerations for 1-Second Periods (Si )* 0.417g
Site Coefficient Fa per Table 1613.3.3(1) 1.067
Site Coefficient Fv per Table 1613.3 .3(2) 1.583
Site Modified Spectral Acceleration for Short Periods (SMS) for Site Class D
[Note: SMS = FaSs] 1155 . g
Site Modified Spectral Acceleration for 1-Second Periods (SMI) for Site Class D
[Note: SMI=FVSI] 0.66g . g
Design Spectral Acceleration for Short Periods (SDS) for Site Class D
[Note: SDS = (213)SMs] 0.77g 7g
Design Spectral Acceleration for 1-Second Periods (SDI) for Site Class D
[Note: SDI = (2/3)SMi] 0.44g . g
Mapped Risk Coefficient at 0.2 sec Spectral Response Period, CRS (per ASCE 7) 0.968
Mapped Risk Coefficient at 1 sec Spectral Response Period, CR1 (per ASCE 7) 1.02
* From USGS, 2013
Section 1803.5,12 of the 2013 CBC (per Section 11.8.3 of ASCE 7) states that the maximum considered
earthquake geometric mean (MCEG) Peak Ground Acceleration (PGA) should be used for geotechnical
evaluations. The PGAM for the site is equal to 0.453g (USGS, 2013).
A deaggregation of the PGA based on a 2,475-year average return period indicates that an earthquake
magnitude of 6.79 at a distance of approximately 11.4 km (7:1 mile) from the site would contribute the most
to this ground motion (USGS, 2008b).
Gorrosivity to Concrete and Metal
The National Association of Corrosion Engineers (NACE) defines corrosion as "a deterioration of a
substance or its properties because of a reaction with its environment." From a geotechnical viewpoint, the
"environment" is the prevailing foundation soils and the "substances" are the reinforced concrete foundations
Project No. 133023-06 Page 6 April 14, 2015
or various buried metallic elements such as rebar, piles, pipes, etc., which are in direct contact with or within
close vicinity of the foundation soil.
In general, soil environments that are detrimental to concrete have high concentrations of soluble sulfates
and/or pH values of less than 5.5. ACI Criteria (ACI 318R-08 Table 4.3.1), provides specific guidelines for
the concrete mix design when the soluble sulfate content of the soils exceeds 0l percent by weight or 1,000
ppm. The minimum amount of chloride ions in the soil environment that are corrosive to steel, either in the
form of reinforcement protected by concrete cover, or plain steel substructures such as steel pipes or piles, is
500 ppm per California Test 532.
Based on limited soil testing prior to the grading of the site, the onsite soils are classified as having a
negligible sulfate exposure condition in accordance with ACT 318R-08 Table 4.3.1. Concrete in contact with
onsite soils should be designed in accordance with ACT 318R-08 Table 4.3..1 for the negligible, category.
Preliminary testing of some of the finish grade soils in PA 13 indicated. chloride contents of up to 1,200 ppm.
In addition, it is our opinion that the onsite soils should be considered moderately to severely corrosive to
buried metals. The actual corrosivity of the finish grade soils should be verified with confirmatory sampling
and testing upon completion of the site roughL and fine-grading.
Control of Surface Water and Drai,zage Gontrol
Positive drainage of surface water away from structures is very important. No water should be allowed to pond
adjacent to buildings. Positive drainage may be accomplished by providing drainage away from buildings at a
gradient of at least 2 percent for a distance of at least 5 feet, and further maintained by a swale or drainage path
at a gradient of at least 1 percent. Where necessary, drainage paths may be shortened by use of area drains and
collector pipes.
Planters with open bottoms adjacent to buildings should be avoided, Planters should not be designed adjacent
to buildings unless provisions for drainage, such as catch basins, liners, and/or area drains, are made.
Overwatering must be avoided.
Limitations
Our services were performed using the degree of care and .skill ordinarily exercised, under similar
circumstances, by reputable engineers and geologists practicing in this or similar localities. No other
warranty, expressed or implied, is made as to the conclusions and professional advice included in this report.
Changes in conditions must be evaluated by the project soils engineer and geologist and design(s) adjusted as
required or alternate design(s) recommended.
This report is issued with the understanding that it is the responsibility of the owner, or of his/her
representative, to ensure that the information and recommendations contained herein are brought to the
attention of the architect and/or project engineer and incorporated into the plans, and the necessary steps are
taken to see that the contractor and/or subcontractor properly implements the recommendations in the field.
The contractor and/or subcontractor should notify the owner if they consider any of the recommendations
presented herein to be unsafe.
Project No. 133023-06 Page 7 April 14, 2015
d:
Closure
This letter is issued with the understanding that it is the responsibility of the owner, or of his/her
representative, to ensure that the information and recommendations contained herein are brought to the
attention of the structural/foundation engineer and the necessary steps are taken to see that the information is
implement in the structural/foundation design, as necessary,
If you should have any questions, please do not hesitate to contact us, The undersigned can be reached at
(661) 702-8474.
Respectfully submitted,
LGC Valley, Inc. -AL
K. c /
lit
c (
Basil Hattar, GE 273
Principal Engineer
Owa-~'
Randall Wagner, CEG 1612
Senior Project Geologist
RKWLB lB
Attachments: References
Distribution: (1) Addressee
Project No. 133023-06 Page 8 April 14, 2015
References
American Society of Civil Engineers (ASCE), 2013, Minimum design loads for buildings and other structures,
ASCE/SEI 7-10, Third Printing, 2013.
California Building Standards Commission (CBSC), 2013a, California Building Code, California Code of
Regulations, Title 24, Part 2, Volume I and 2 of 2 (based on the 2012 International Building Code).
CBSC, 2013b, California Residential Building Code, California Code of Regulations, Title 24, Part 2.5,(based on
the 2012 International Residential Code).
CBSC, 2013c, California Green Building Standards Code, California Code of Regulations, Title 24, Part ii.
LGC Valley, Inc., LGC Valley, Inc., 2014, Geotechnical and environmental recommendations for Robertson
Ranch West, Carlsbad Tract No. 13-03, Carlsbad, California, Project Number 133023-03, dated 4/29/14.
O'Day Consultants, 2013, Grading plans for Rancho Costera, Robertson Ranch West Village, Carlsbad Tract No.
13-03, Drawing No. 480-3A, 26 sheets, dated November 25.
O'Day Consultants, 2014, Vesting tentative map for Carlsbad Tract No. 13-03-2,23 sheets, dated 1/16/2014.
Post-Tensioning Institute, 2006, Design of post tensioned slabs-on-ground, Third Addition, Addendum I dated
May 2007, and Addendum 2 dated May 2008, with errata February 4, 2010.
United States Geological Survey (USGS), 2008a, "2008 National Seismic Hazard Maps - Fault Parameters"
retrieved from: http://geohazai-ds.usgs.gov/cfusion/liazfatiIts search/hf search main.cfm
USGS, 2008b, "2008 Interactive Deaggregations (Beta)," retrieved from-
https:Hgeohazards.usgs.gov/deaggint/2008
USGS, 2013, U.S. Seismic Design Maps, retrieved from:
http://geohazards.usgs.gov/designmaPS/Lis/batch.php#csv
Project No. 133023-06 Page 9 April 14, 2015
C 0 N S U L T A/N T S
Civil Engineering • Surveying
January 20, 2017
J.N. 10-1307-1
City of Carlsbad Public Works Inspector
ATTN: Grant Clavier
1635 Faraday Avenue
Carlsbad, CA 92008
RE: Rancho Costera
Lots 35 through 43, 55 through 59, 252 through 255, 261 through 267, 271 through 275, 282
through 287, 292 through 298 and 302 through 307 of Map CT 13-03, Map No. 16092
Dear Grant,
Based upon topographic surveys performed by O'Day Consultants on December 3 and 4, 2015
for Lots 35 through 260 and Lots 271 through 275, and March 8, 22 and 31, 2016 for Lots 38
through 43, 55 through 59, 252 through 255, 261 through 267, 282 through 287, 292 through 298
and 302 through 307, the rough grading for land development has been completed within
standard tolerance (0.10 feet) in accordance with the approval plan, (City of Carlsbad DWG.
480-3A) and that all embankments, cut slopes and pad sizing are as shown on the approved plans
for lots 35 through 43, 55 through 59, 252 through 255, 261 through 267, 271 through 275, 282
through 287, 292 through 298 and 302 through 307.
We request the release of pads for building permits for lot 35 through 43, 55 through 59, 252
through 255, 261 through 267, 271 through 275, 282 through 287, 292 through 298 and 302
through 307.
Very truly yours,
O'DAY CONSULTANTS, INC.
GO/tan
George ay
Project Manager
O'Day Consultants Inc. E-mail: oday@odayconsultants.com
2710 Loker Avenue West, Suite 100 Website: www.odayconsultants.com
Carlsbad, California 92010-6609 Tel: 760.931.7700 Fax: 760.931.8680