HomeMy WebLinkAboutCT 02-14-05; BRESSI RANCH PA 10 UINT 5; SUPPLEMENTAL GEOTECHNICAL INVESTIGATION; 2001-03-144
Leighton and Associates, Inc.
A LEIGHTON GROUP COMPANY
To:
March 14, 2001
ProjectNo. 971009-005
Lennar Homes
5780 Fleet Street, Suite 320
Carlsbad, Califomia 92008
Attention: Mr. Jim Urbina
Subject: Supplemental Geotechnical Investigation for Mass Grading, Bressi Ranch, Carlsbad, Califomia
In accordance with your request, we have performed a supplemental geotechnical investigation for the Bressi Ranch
property located southeast of the intersection of El Camino Real and Palomar Airport Road in Carlsbad, Califomia. The
purpose ofthis report was to update the results of our preliminary geotechnical report for the site (Leighton, 1997) and
to evaluate the existing geologic and geotechnical aspects of the proposed mass grading ofthe site relative to the latest
200-scale tentative tract map/grading plans. This report presents the results of our supplemental subsurface
investigation and geotechnical analysis, and provides a summary of our conclusions and recommendations reladve to
the mass grading of the site.
Based on the resuhs of our supplemental investigation and review of the previous geotechnical reports pertinent to the
subject site, the proposed development of the site for commercial and residential uses is considered feasible from a
geotechnical standpoint provided the recommendations summarized in this report are implemented during the site
grading operations. It should be noted that additional geotechnical evaluation of the site (including additional field
studies, laboratory testing, and slope stability analysis) and a grading plan review will be needed after more detailed
grading plans (i.e. 40-scale grading plans) for the different planning areas ofthe site are developed.
If you have any questions regarding our report, please contact this office. We appreciate this opportunity to be of
service.
Respectfully submitted,
LEIGHTON AND ASSOCIATES, INC.
Tim J. Lawson, RCE 53388
Principal Consulting Engineer
Randall K. Wagner, CEG 1612
Director of Geology
Distribution: (10) Addressee
(2) Lennar Homes, Attention: Mr. Dale Greenhaigh
(1) PDC, Attention: Ms. Marina Wurst
\
3934 Murphy Canyon Road, Suite B205
858.292,8030 • Fax 858.292.0771
San Diego, CA 92123-4425
www.leightongeo.com
4971009-005
TABLE OF CONTENTS
Section Page
1.0 INTRODUCTION 1
1.1 PURPOSE AND SCOPE OF SERVICES 1
1.2 SFTE DESCRIPTION 1
1.3 PROPOSED DEVELOPMENT 3
1.4 SUPPLEMENTAL SURFACE INVESTIGATION AND LABORATORY TESTING 3
2.0 GEOTECHNICAL CONDITIONS 5
2.1 REGIONAL GEOLOGY 5
2.2 SITE-SPECIFIC GEOLOGY 5
2.2.1 Documented Fill Soils (Map Symbol -Af) 5
2.2.2 Undocumented Fill Soils (Map Symbol - Afu) 5
2.2.3 Topsoil (Unmapped) 6
2.2.4 Alluvium/ Colluvium, Undifferentiated (Map Symbol - Qal/Qcol) 6
2.2.5 Landslide Deposits (Map Symbol - Qls) 6
• 2:2.6 Santiago Formation (Map Symbol -Ts) 7
2.3 GEOLOGIC STRUCTURE 8
2.4 FAULTING g
2.5 SEISMIC CONSIDERATIONS 9
2.5.1 Liquefaction and Dynamic Settlement p
2.5.2 Uniform Building Code Seismic Parameters , 9
2.6 GROUNDWATER 10
2.7 ENGINEERING CHARACTERISTICS OF ON-SITE SOILS 10
2.7.1 Expansion Potential 10
2.7.2 Soluble Sulfate Content 7/
2.7.3 Excavation Characteristics U
2.7.4 Earthwork Shrinkage and Bulking U
2.8 SLOPE STABILITY 12
2.9 SETTLEMENT OF DEEP FILLS 12
3.0 CONCLUSIONS 13
40 RECOMMENDATIONS 15
4.1 EARTHWORK 15
4.1.1 Site Preparation 75
4.1.2 Removal and Recompaction of Unsuitable Soils 75
4.1.3 Excavations 77
4.1.4 Cut/Fill Transition Conditions 77
4.1.5 Fill Placement and Compaction 77
4.1.6 Settlement of Deep Fills 77
4.1.7 Expansive Soils and Selective Grading IS
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TABLE OF CONTENTS (Continued)
Section Page
4.2 SLOPE STABILFTY 18
4.2.1 Deep-Seated Stability 19
4.2.2 Surficial Stability 21
4.3 CONTROL OF GROUND WATER AND SURFACE WATERS 21
4.3.1 Canyon Subdrains 22
4.3.2 Buttress and Stability Fill Subdrains 22
4.3.3 Cut Slope Seepage Conditions 22
4.4 SETTLEMENT MoNtroRiNG 23
4.5 SURFACE DRAINAGE AND LOT MAINTENANCE 23
4.6 GRADED SLOPES 23
4.7 PLAN REVIEW AND CONSTRUCTION OBSERVATION 24
5.0 LIMITATIONS 25
FIGURES
FIGURE i - SITE LOCATION MAP - PAGE 2
FIGURES 2 THROUGH 14 - GEOLOGIC CROSS-SECTIONS A-A' THROUGH M-M' - IN POCKET
TABLES
TABLE 1 - GEOTECHNICAL SUMMARY OF EXISTING LANDSLIDES - REAR-OF-TEXT
TABLE 2 - EARTHWORK SHRINKAGE AND BULKING ESTIMATES - PAGE 11
TABLE 3 - SLOPE STABILITY SOIL PARAMETERS - PAGE 19
PLATES
PLATE 1 - GEOTECHNICAL MAP - IN POCKET
PLATE 2 - REMEDL«. GRADING MAP - IN POCKET
APPENDICES
APPENDIX A - REFERENCES
APPENDEX B - BORING AND TRENCH LOGS
APPENDIX C - LABORATORY TEST PROCEDURES AND TEST RESULTS
APPENDIX D - GENERAL EARTHWORK AND GRADING SPECIFICATIONS FOR ROUGH-GRADING
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1.0 INTRODUCTION
1.1 Purpose and Scope of Services
This report has been prepared in accordance with your request and presents the results of our
supplemental geotechnical investigation of the Bressi Ranch for mass grading purposes. Bressi
Ranch is located southeast of the intersection of El Camino Real and Palomar Airport Road in the
City of Carlsbad, Califomia (Figure 1). The purpose of this report was to update the results of our
preliminary geotechnical report for the site (Leighton, 1997) and to evaluate the existing geologic
and geotechnical aspects of the proposed mass grading of the site relative to the latest 200-scale
tentative tract map/grading plans. Our scope of services included the following:
• Review of pertinent available geotechnical literature (including previous geotechnical reports of
Bressi Ranch, Rancho Carrillo, and La Costa - The Greens developments), geologic maps, and
aerial photographs (Appendix A).
• Reconnaissance and geologic mapping of the site.
• A supplemental subsurface exploration program consisting of the excavation, sampling and
logging of 8 large-diameter exploratory borings and 56 exploratory trenches across the site. The
large-diameter borings and trenches were excavated to evaluate the characteristics of the
subsurface soils. Logs of the borings and trenches are presented in Appendix B. Included in
Appendix B, are logs of previous borings and trenches excavated by Leighton and others that
are pertinent to the development of Bressi Ranch.
• Laboratory testing of representative samples obtained during our preliminary and supplemental
subsurface exploration programs (Appendix C).
• Geotechnical analysis of the data accumulated during our supplemental investigation including
seismic and slope stability analysis.
• Preparation of this report presenting our findings, conclusions and recommendations including
General Earthwork and Grading Specifications for Rough Grading (Appendix D) with respect
to the proposed mass grading of the site. The approximate limits of the geologic units
encountered and the boring and trench locations applicable to the development of the site are
presented on the Geotechnical Map (Plate 1), Remedial Grading Map (Plate 2), and Cross-
Sections A-A' through M-M' (Figures 2 through 14). The 200-scale Tentative Tract
Map/Grading Plan (PDC, 2001b), was utilized as base map for the Geotechnical Map (Plate 1)
and the Remedial Grading Map (Plate 2).
1.2 Site Description
The subject property, with a total acreage of approximately 600 acres, is located southeast of the
intersection El Camino Real and Palomar Airport Road in the City of Carlsbad, Califomia (Figure
1). The site consists of an irregular-shaped piece of property bordered on the north by Palomar
Airport Road, on the west by El Camino Real, on the southwest and south by the La Costa - The
Greens property, and by the Rancho Carrillo development and Melrose Drive to the east.
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BAS E MAP : Thomas Bros. GeoFlnder for
Windows, San Diego County, 1995, Page 1127 0 1000 2000 4000
1 "=2,000'
Scale in Feet
Lennar / Bressi Ranch
Cartsbad, California
SITE
LOCATION
MAP
Project No.
971009-005
Date
March ZOol-eightOPi gure No. 1
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Topographically, the site generally consists of a an east-west trending relatively large and flat
ridgeline in the northem section of the site and a north-south trending central ridge in the south
central portion of the site. The north-south trending central ridge is flanked by two large north-south
trending drainages and associated tributaries forming the gently sloping hillside and valley terrain in
the south central portion of the property. A large east-west trending drainage is located in the far
southem portion of the site. Elevations on the site range from a high of approximately 465 feet
mean sea level (msl) in the north central portion of the site to a low of approximately 125 feet msl
within the major east-west drainage in the southem portion of the site.
Natural drainage is presently accomplished through a network of minor ravines and ultimately
through the east-west trending canyon in the southem portion of the site. Vegetation on the site
ranges from remnant vegetable crops, native grasses, and weeds on the flat ridge tops, wide canyon
bottoms and on the hillsides; and minor to thick chaparral and trees (mainly on the steep hillsides
and the narrow canyon bottoms) in the central and southwestem portions of the site. Man-made
features on the site include: 1) a single-family residence in the central portion of the site; 2) a guard
shack at the northem site entrance; 3) two building foundations and several relatively small
detention basins (associated with prior farming activities); 4) existing SDG&E, water and sewer
line easements crossing the site in westem, central and southem portions of the site; 5) several dirt
roads which cross the property, and 6) fences along the perimeter of the property.
1.3 Proposed Development
Detailed site grading and development plans were not available as of the date of this report.
However, we understand that the proposed site development will include 13 planning areas across
the site for light industrial, commercial, and residential purposes. In general, the light industrial
planning areas are located in the northem portion of the site along Palomar Airport Road while the
commercial planning areas are in the south and southeastem portion of the site. The residential
planning areas are generally located in the central and southwestem portion of the site.
Approximately 445 acres of the site will be graded while the remaining acreage will be left as open
space. Preliminary calculations of the earthwork quantities indicate the grading will entail
approximately 6 million yards of cut and fill material (PDC, 2001a).
We also understand that development of the Bressi Ranch will include 1) constmction of Poinsettia
Lane from its existing terminus at the southeastem portion of the site through the Bressi Ranch
property and possibly to El Camino Real; 2) construction of El Fuerte Road from Palomar Airport
Road to existing portion of the road south of the Bressi Ranch Property; and 3) improvements to El
Camino Real along the northwestem side of the Bressi Ranch Property. In addition, the
development will include relatively large open space areas, interior streets, underground utilities,
and other associated improvements.
1.4 Supplemental Surface Investigation and Laboratory Testing
Our supplemental subsurface investigation consisted of the excavation, logging and sampling of 8
large-diameter borings (utilizing a bucket-auger drill rig) and the excavation of 56 exploratory
trenches (in addition to the previously excavated 7 small-diameter borings, 21 large-diameter
borings and 30 exploratory trenches The borings and trenches were excavated to a maximum depth
of approximately 116 and 15 feet, respectively. The large-diameter borings were entered by our
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geologist and down-hole logged. Logs of the borings and trenches are presented in Appendix B.
The approximate locations of the borings are shown on the Geotechnical Map (Plate 1) and Cross-
Sections A-A' through M-M' (Figures 2 through 14). Subsequent to the subsurface investigation,
the borings and trenches were backfilled.
Appropriate laboratory testing was performed on representative soil samples obtain during our
preliminary and supplemental subsurface investigations. The laboratory tests included
moisture/density determinations, Atterberg Limits (e.g. liquid limit and plastic limit), undisturbed
and remolded direct shear, maximum dry density and expansion index tests. A discussion of the
tests performed and a summary of the test results are presented in Appendix C. The
density/moisture determinations of the undisturbed samples obtained from the borings are shown on
the boring logs (Appendix B).
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2.0 GEOTECHNICAL CONDITIONS
2.1 Regional Geologv
The subject site is located within the coastal subprovince of the Peninsular Ranges Geomorphic
Province, near the westem edge of the southem Califomia batholith. The topography at the edge of
the batholith changes from the mgged landforms developed on the batholith to the more subdued
landforms that typify the softer sedimentary formations of the coastal plain. Specifically, the site is
underlain by the sedimentary units of the Tertiary-aged Santiago Formation. Subsequent to the
deposition of this unit, erosion and regional tectonic uplift created the valleys and ridges of the area.
Recent weathering and erosional processes have produced the Quatemary surficial units including
alluvium, colluvium, landslide deposits, and topsoil that mantle the site.
2.2 Site-Specific Geologv
Formational materials of the Tertiary-aged Santiago Formation and surficial units consisting of
landslide deposits, colluvium, alluvium, topsoil and artificial fill soils were encountered during our
preliminary and supplemental investigations of the site. The areal distributions of the geologic units
are presented on the Geotechnical Map (Plate 1). Our interpretation of the subsurface geologic
conditions is also indicated on Geologic Cross Sections A-A' through M-M' (Figures 2 through 14).
Each of the geologic units present on the site is described below (youngest to oldest).
2.2.1 Documented Fill Soils (Map Symbol - Af)
As observed, the documented fill was associated with prior grading of the Poinsettia
Lane, El Fuerte Road, Palomar Airport Road, and Melrose Drive roadway alignments.
As-graded Geotechnical Reports documenting the fill placement and grading operations
(Appendix A) indicate the fill soils were placed at 90 percent relative compactions.
However, we anticipate that the upper portion of the fill may have become desiccated
and minimal removals (i.e. on the order of 1 to 5 feet) may be needed prior to the
placement of additional fill. In addition, we anticipate the removal of unsuitable soils
along the perimeter of the fills were not made outside a 1:1 (horizontal to vertical)
projection from the existing toe-of-slope down to competent formational material
undemeath the fill.
2.2.2 Undocumented Fill Soils (Map Svmbol - Afu)
Undocumented fill soils were observed in a number of places on the site. The
undocumented fill was generally associated with the grading of the on-site dirt roads,
retention basins, and prior farming activities. These fill soils are estimated to range from 1
to 25 or more feet in depth, and generally consist of dry to damp, loose or soft sand and
clay. All existing fills located within the limits of grading should be considered potentially
compressible and unsuitable in their present state for stmctural support. The undocumented
fill soils should be removed to competent formational material within the limits of the
proposed grading.
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2.2.3 Topsoil (Unmapped)
The topsoil encountered during our field investigation mantles the majority of the site. The
topsoil, as observed, consisted predominantly of a light-brown to brown, damp to moist,
mediimi dense to stiff, sandy to silty clay and some clayey to silty sands. These soils were
generally massive, porous, and contained scattered roots and organics. The unsuitable
topsoil is estimated to be fi-om 1 to 4 feet in thickness; however, localized areas of thicker
accumulations of topsoil may be encountered during grading.
2.2.4 Alluvium/ Colluvium. Undifferentiated (Map Symbol - Oal/Ocol)
Potentially compressible deposits of alluvium were encountered in the major and most of
the tributary drainage courses on the site. In addition, our field investigation indicated that
potentially compressible deposits of colluvium mantle the middle and lower portions of the
on-site natural slopes (especially slopes comprised of the Santiago Formation claystone)
and in the upper portions of the tributary drainage courses throughout the site.
During our supplemental investigation, we did not differentiate the alluvial and colluvial
deposits and therefore, these soils are mapped and presented as undifferentiated
alluvium/colluvium on the geologic maps and cross-sections. As observed, these deposits
typically consist of light orange-brown to brown sands, sandy clays and clayey sands that
are porous and contain scattered organics. Both the alluvium and colluvium are considered
potentially compressible in the present state. In general, the alluvium/colluvium is
estimated to be 4 to 15 feet thick in the tributary canyons, however deeper accumulations
may be present. The alluvium encountered in the proposed El Fuerte Road drainage and the
main east-west rending canyon in the southem portion of the site (along proposed
Poinsettia Lane) have alluvial thicknesses on the order of 40 to 50 or more feet. Relatively
shallow ground water (generally less than 5 to 20 feet in depth) was observed in these
alluvial soils.
2.2.5 Landslide Deposits (Map Svmbol - Ols)
Several landslides have been identified within the subject property. The approximate limits
of these landslides are shown on the Geotechnical Map (Plate 1) and the Remedial Grading
Map (Plate 2). To aid in the discussion of the landslides, each landslide and/or landslide
complex has been Numbered 1 through 24 (as indicated on the Remedial Grading Map). It
should be noted that several of these landslides are outside the limits of grading while
others extend beyond the property boundaries. A geotechnical summary including a
description of each numbered landslide/landslide and the preliminary recommendations to
mitigate the landslide is also presented on Table 1 (presented at the rear of the text).
The landslide deposits include graben material (and associated colluvial soils), relatively
undisturbed blocks of formational material and weathered formational material consisting
of soils characteristic of the on-site bedrock units (i.e. silty sands and silty to sandy clays).
Graben development at the head of the landslides appears to be moderate to relatively
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minor depending on the amount of movement of the landslide. The landslide material is
generally moderately fractured and jointed at depth and highly weathered near the surface
and at the toe of the landslides. The landslide basal mpture surfaces, as observed in the
borings, typically consisted of a paper-thin to 1/4-inch thick remolded clay seams. In
general, the landslide basal mpture surfaces appear to correspond to either an existing clay
seam or a weak zone in the formational claystone.
Several of the smaller landslides shown on the Geotechnical Map (Plate 1) are shallow
surficial slumps/debris fiow deposits (generally less than 5 to 15 feet thick). These shallow
surficial slumps or debris flows appear to have developed as a result of prior landslide
activation, seepage zones and/or oversteepened canyon side-walls within highly weathered
portions of the formational soils.
Due to potentially instability concems and compressible nature, the landslide deposits
within the limits of the planned grading are considered unsuitable for stmctural support in
their present condition and remedial measures (i.e. buttressing with fill and/or removals of
the unstable and potentially compressible portions) will be required. Preliminary
recommendations for the stabilization of the landslides are presented in Section 4.2, on
Table 1, and indicated on the Remedial Grading Map (Plate 2).
With regard to the ancient landslides, site development appears feasible from a
geotechnical standpoint. However, Landslides Numbers 5, 9, 9A, and 12, all of which,
extend off-site (or outside the proposed limits of grading).may require off-site grading in
order to mitigate the landslide.
2.2.6 Santiago Formation (Map Svmbol - Ts)
The Tertiary-aged Santiago Formation, as encountered during our field investigation,
consists primarily of massively bedded sandstones and claystones/siltstones. The siltstones
and claystones generally are olive green to gray (unweathered), damp to moist, stiff to hard,
moderately weathered, fractured and sheared. The sandstone generally consists of orange
brown (iron oxidized staining) to light brown, damp to moist, dense to very dense, silty fine
to medium grained sandstone. In previous reports this unit was classified and mapped as the
Delmar Formation and Torrey Sandstone. Recent publications (including Tan and
Kennedy, 1996) classify these units in north San Diego County as the Santiago Formation.
When reviewing the boring and trench logs from previous investigations, this recent change
should be taken into account.
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2.3 Geologic Stmcture
The general stmcture of the bedrock appears to be near horizontal. Based on the subsurface data,
bedding within the Santiago Formation generally exhibits variable bedding with strikes ranging
from northwest to northeast and dips typically 5 to 15 degrees to the southeast and northwest.
Locally, cross bedding was observed with dips steeper than 15 degrees. Clay seams and/or landslide
mpture surfaces encountered in the borings generally trend parallel to the bedding.
Jointing on-site is very variable, but predominantly trends 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 mainly in the Santiago Formation claystone and
siltstone. Numerous wide, diffuse zones of shearing, as well as more well-defined zones, were
encountered in the bedrock, and are thought to be the resuh of regional tectonic shearing of the
relatively stiff and unyielding siltstone and claystone.
2.4 Faulting
Our discussion of faults on the site is prefaced with a discussion of Califomia legislation and state
policies conceming the classification and land-use criteria associated with faults. By definition of
the Califomia Mining and Geology Board, an active fault is a fauh that has had surface
displacement within Holocene time (about the last 11,000 years). The State Geologist has defined a
potentiallv active fault as any fault considered to have been active during Quatemary time (last
1,600,000 years) but that has not been proven to be active or inactive. This definition is used in
delineating Fault-Rupture Hazard Zones as mandated by the Alquist-Priolo Earthquake Fault
Zoning Act of 1972 and as most recently revised in 1997. The intent of this act is to assure that
unwise urban development does not occur across the traces of active faults. Based on our review of
the Fault-Rupture Hazard Zones, the site is not located within any Fault-Rupture Hazard Zone as
created by the Alquist-Priolo Act (Hart, 1997).
San Diego, like the rest of southem Califomia, is seismically active as a resuh of being located near
the active margin between the North American and Pacific tectonic plates. The principal source of
seismic activity is movement along the northwest-trending regional fault zones such as the San
Andreas, San Jacinto and Elsinore Faults Zones, as well as along less active faults such as the Rose
Canyon Fault Zone.
Our review of geologic literature pertaining to the site and general vicinity indicates that there are
no known major or active faults on or in the immediate vicinity of the site (Weber, 1982, and
Jennings, 1994). Evidence for faulting was not encountered during our field investigation. The
nearest known active fault is the Rose Canyon Fauh Zone, which is considered a Type B Seismic
Source based on the 1997 Uniform building Code (UBC), and is located approximately 7.0 miles
(11.2 kilometers) west of the site. Because of the lack of known active fauhs on the site, the
potential for surface rupture at the site is considered low.
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2.5 Seismic Considerations
The principal seismic considerations for most stmctures in southem Califomia are surface mpturing
of fauh traces and damage caused by ground shaking or seismically induced ground settlement. The
possibility of damage due to ground mpture at the site is considered low since active fauhs are not
known to cross the site. Hazards from seiches and tsunamis are not present as the site is located
away from the immediate coastal area and there are no large standing bodies of water in or near
the site.
The seismic hazard most likely to impact the site is ground-shaking resulting from an earthquake on
one ofthe major regional fauhs. The effects of seismic shaking can be reduced by adhering to the
most recent edition of the Uniform Building Code and design parameters of the Stmctural
Engineers Association of Califomia.
2.5.1 Liquefaction and Dvnamic Settlement
Liquefaction and dynamic settlement of soils can be caused by strong vibratory motion due
to earthquakes. Research and historical data indicate that loose granular soils underlain by a
near-surface ground water table are most susceptible to liquefaction, while the stability of
most silty clays and clays is not adversely affected by vibratory motion. Because of the
dense nature of the underlying formational material and lack of a shallow permanent
groundwater table, it is our opinion that the potential for liquefaction or seismically induced
dynamic settlement across the majority of the site due to the design earthquake is low.
However, relatively shallow groundwater and loose sandy soils are present in the main
canyons and the potential for liquefaction of these in considered moderate unless
provisions to mitigate the potential liquefaction are not performed during site grading. We
anticipate that after the removal of the unsuitable material above the ground water table,
placement of fill soils on the order of 15 to 20 feet above the current grades in these areas
and consolidation of the saturated sandy soils occur (after the placement of the fill soils),
the potential for surface manifestation of liquefaction in these areas will be low.
2.5.2 Uniform Building Code Seismic Parameters
The site is located within Seismic Zone 4. The closest active fauh is the Rose Canyon Fauh
Zone, which is considered a Type B Seismic Source (per 1997 UBC criteria) and is located
approximately 7.0 miles (11.2 kilometers) west of the site. The closest Type A Seismic
Source is the Julian segment of the Elsinore Fauh Zone, which is located approximately
23.5 miles (38 kilometers) east of the site. The soil profile type at the site, following the
planned grading is anticipated to be Sc. Near source factors of Na = 1.0 and Nv= 1.0 are
considered appropriate base on the seismic setting.
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2.6 Ground Water
Ground water was encountered in a number of the exploratory borings and trenches excavated
across the site. Random seepage zones were also encountered in some of the exploratory borings
and surface water was observed in the south flowing drainage on the west side of the site and in the
large west flowing drainage (along proposed Poinsettia Lane) in the southernmost portion of the
site. The approximate depths and elevations of the encountered ground water are depicted on the
boring and trench logs (Appendix B). The ground water table encountered in the main drainages is
generally perched ground water within the alluvial soils. The ground water that was encountered in
the main canyons of the site at the time of our preliminary and supplemental investigations was
approximately 5 to 20 feet below the existing ground surface. Ground water seepage zones in the
on-site formational material was encountered at slightly elevated depths relative to the ground water
depths in the adjacent drainages as the ground water table will generally follow the overlying
topography, although with less relief Seasonal fluctuations of surface water and ground water
should be expected.
Subdrains are recommended in the canyon removal areas and the buttress and stability fills as
indicated in Appendix D. The approximate location of recommended canyon subdrains are depicted
on the Remedial Grading Map (Plate 2). Specific subdrain recommendations will be made when
more detailed grading plans are developed. It should be noted that ground water levels might vary at
the time of construction from those elevations encountered during our preliminary and
supplemental investigations. Since the elevations at which ground water was encountered were
generally below anticipated finish grade elevations, it is our opinion that ground water related
problems should be minimal provided the recommendations presented in this report are
incorporated into the design and constmction of the project. It is our recommendation, however,
that periodic inspection be made by either our soil engineer or engineering geologist during the
grading operations and/or constraction for the presence of ground water. Remedial measures, if any,
can be recommended on a case-by-case basis during the grading and construction operations.
2.7 Engineering Characteristics of On-site Soils
Based on the results of our current geotechnical investigation, previous geotechnical investigations
of the site (Appendix A), laboratory testing of representative on-site soils, and our professional
experience on adjacent sites with similar soils, the engineering characteristics of the on-site soils are
discussed below.
2.7.1 Expansion Potential
The expansion potential of the on-site soils ranges from very low to very high. The
sandstone within the Santiago Formation and sandy surficial soils are anticipated to be in
the very low to moderate expansion range. The siltstone and claystone of the Santiago
Formation, as well as the clayey topsoil, alluvium, and colluvium are anticipated to have a
medium to very high expansion potential. Geotechnical observation and/or laboratory
testing upon completion of the graded pads are recommended to determine the actual
expansion potential of finish grade soils on the graded lots. To reduce the possibility of
having expansion soils at or near finish pad grades, the clayey soils should be placed in
deeper fill areas or outside the limits of the building pads. In addition, building pads
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consisting of highly expansive soils may be overexcavated and replaced with fill soils
having a lower expansion potential.
2.7.2 Soluble Sulfate Content
Based on our professional experience on adjacent sites, the on-site soils should posses a
negligible to moderate soluble sulfate content. However, some of the soils may possess a
high sulfate content. Laboratory testing should be performed on the soils placed at or near
finish grade after completion of site grading.
2.7.3 Excavation Characteristics
With the exception of localized cemented zones within the Santiago Formation, it is
anticipated that the on-site sedimentary and surficial soils may be excavated with
conventional heavy-duty constmction equipment. Localized cemented zones may require
heavy ripping. If a significant amount of oversize material (typically over 8 inches in
maximum dimension) is generated, it should be placed to prevent possible settlement ofthe
soil around the rocks, as recommended in Section 4.1 and Appendix D.
2.7.4 Earthwork Shrinkage and Bulking
The volume change of excavated on-site materials upon recompaction as fill is expected to
vary with materials and location. Typically, the surficial soils and bedrock materials vary
significantly in natural and compacted density, and therefore, accurate earthwork
shrinkage/bulking estimate cannot be determined. However, the following factors (based on
the results of our subsurface investigations, laboratory testing, geotechnical analysis and
professional experience on adjacent sites) are provided on Table 2 as guideline estimates. If
possible, we suggest an area where site grades can be adjusted be provided as a balance
area.
Table 2
Earthwork Shrinkage and Bulking Estimates
Geologic Unit Estimated Shrinkage/bulking
Topsoil/Alluvium/Colluvium 5 to 15 percent shrinkage
Landslide Deposits 0 to 10 percent shrinkage
Santiago Formation 3 to 7 percent bulking*
* The clayey and more cemented sandy soils of the Santiago Formation are
anticipated to bulk more than the slightly friable sands.
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2.8 Slope Stabilitv
Our review of the 200-scale tentative tract map/grading plan (PDC, 2001b) indicates that the
proposed cut and fill slopes on the site are proposed at a maximum inclination of 2:1 (horizontal to
vertical) and up to approximately 50 and 70 feet in height, respectively. Our analysis indicates that
the proposed fill slopes will have a deep-seated factor of safety of at least 1.5. With regard to
natural slopes, our geotechnical analysis indicates the natural slopes should be grossly stable
provided unforeseen geologic conditions are not present. However, our analysis indicates that some
of the proposed cut slopes (especially cut slopes composed of claystones/siltstones of the Santiago
Formation) may be surficially unstable and remedial measures such as the constraction of
replacement/stability fills along the slope faces will be required.
Slope stability analysis was also performed in areas underlain by landslides. Our analysis indicates
that buttresses will be required in order to provide a minimum factor-of-safety of 1.5 or greater for
slopes or grading pads proposed in areas of landslides. The recommended preliminary buttresses are
presented on the Remedial Grading Map (Plate 2) and on the applicable Geologic Cross-Sections
(Figures 2 through 14). It should be noted that additional analysis will be required after more
detailed grading plans are developed. Specific preliminary recommendations conceming the
stability of the slopes are presented in Section 4.2.
2.9 Settlement of Deep Fills
Settlement of deep compacted fill soils occurs in two manners. One is short-term (elastic)
settlement due to the weight of the overlying fill soils compressing the soil and driving the water out
of the soil structure (consolidation). This typically occurs during or within a few months after the
completion of grading. In general, silty to clayey soils will compress more slowly than
sandy/granular soils. The second manner is long-term settlement, which typically occurs on the
order of years after the fill soils are placed and is triggered by the additional wetting of the soils due
to irrigation/precipitation. This occurs even to properly compacted fill soils and even though
subdrains are installed. Silty to clayey soils typically settle as much as two times the amount that
sandy soils will. Preliminary recommendations are presented in Sections 4.1.6 and 4.4.
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3.0 CONCLUSIONS
Based on the resuhs of our supplemental geotechnical investigation at the subject site and our review ofthe
previous geotechnical reports applicable to the site (Appendix A), it is our professional opinion that the
proposed mass grading of the Bressi Ranch property is feasible from a geotechnical standpoint, provided the
following conclusions and recommendations are incorporated into the project plans, specifications, and
followed during the site grading operations.
The following is a summary of the geotechnical factors, which may effect development ofthe site.
• Based on our subsurface exploration and review of pertinent geotechnical reports, the site is underlain
by the Santiago Formation, landslide deposits, alluvium, colluvium, topsoil and documented and
undocumented fill soils.
• The undocumented fill, topsoil, colluvium, alluvium and weathered formational materials are
considered unsuitable in their present state and will require removal and recompaction in areas of
proposed development or ftiture fill.
• Due to potentially instability concems and compressible nature, the landslide deposits within the
limits of the planned grading are considered unsuitable for structural support in their present
condition and remedial measures (i.e. buttressing with fill and/or removals of the unstable and
potentially compressible portions) will be required. Preliminary recommendafions for the
stabilization ofthe landslides are presented in Section 4.2, on Table 1, and indicated on the Remedial
Grading Map (Plate 2).
• Sihstone and claystone soils of the Santiago Formation are highly to very highly expansive. These
expansive soils should either be removed where present within 5 feet of finish pad grades and replaced
with soil having a lower expansion potential or a special foundation design (i.e. post-tensioned design)
should be provided.
• The existing on-site soils appear to be suhable material for use as fill provided they are relatively free of
rocks (larger than 8 inches in maximum dimension), organic material and debris.
• Active fauhs are not known to exist on or in the immediate vicinity of the site. Because of the lack of
known active faults on the site, the potential for surface rupture at the site is considered low.
• The main seismic hazard that may affect the site is ground shaking from one of the active regional
fauhs.
• Evidence for fauhing was not encountered during our field investigation. The nearest known active fault
is the Rose Canyon Fauh Zone, which is considered a Type B seismic source based on the 1997
Uniform building Code (UBC), and is located approximately 7.0 miles (11.2 kilometers) west of the
site.
• Due to the clayey and/or relatively dense nature of the on-site soils, the potential for liquefaction and
dynamic settlement of the site is considered unlikely, provided the recommendations for site grading (as
indicated in Section 4.1 and Appendix D) are adhered to. However, relatively shallow groundwater
and loose sandy soils are present in the main canyons and the potential for liquefaction of these in
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considered moderate unless provisions to mitigate the potential liquefaction are not performed during
site grading.
The ground water table was encountered in the on-site alluvium/colluvium at depths from
approximately 5 to 20 feet below the existing ground surface of the main drainages. In general, the
ground water table within the main canyon along proposed Poinsettia Lane is anticipated to be on the
order of 5 to 10 feet in depth while the north-south trending canyons on the west and east sides are on
the order to 10 to 20 feet in depth. Localized seeps were also observed in a number of the large-diameter
borings at various elevations with the formational material. However, ground water on the site is not
anticipated to be a significant factor during site grading and subsequent development. If ground water
seepage conditions are encountered during site development, recommendations to mitigate the
conditions can be made on a case-by-case basis at that time.
The expansion potential of the on-site soils ranges from very low to very high. The sandstone within
the Santiago Formation and sandy surficial soils are anticipated to be in the very low to moderate
expansion range. The siltstone and claystone of the Santiago Formation, as well as the clayey topsoil,
alluvium, and colluvium are anticipated to have a medium to very high expansion potential.
Based on our professional experience on adjacent sites, the on-site soils should posses a negligible to
moderate soluble sulfate content. However, some of the soils may possess a high sulfate content.
With the exception of localized cemented zones within the Santiago Formation, it is anticipated that
the on-she sedimentary and surficial soils may be excavated with conventional heavy-duty
constraction equipment. Localized cemented zones may require heavy ripping.
All oversized material should be placed in accordance with the recommendations presented in Section
4.0 and Appendix D to minimize settlement of the material around the oversized rocks.
In general, when recompacted as fill soils, the surficial units (including landslide deposits, topsoil,
colluvium, alluvium, etc.) are anticipated to shrink and the bedrock materials are likely to bulk.
It is anticipated that any planned major cut slopes that will be comprised of siltstones and/or claystones
of the Santiago Formation will require stabilization measures to mitigate potential surficial instability. A
detailed discussion on slope stability is provided in Section 4.2.
Potential settlement of relatively deep fills is anticipated to mainly occur during or within a few months
following the completion of grading. However, areas of deep fill should be monitored to ensure that the
majority of the settlement occurs prior to constraction of stractures and other settlement sensitive
improvements. In addition, lots underlain by fill differential thicknesses in excess of 20 feet will require
the utilization of a special foundation design (i.e. a post-tensioned slab design).
The potential for long term settlement of the alluvial materials within the main canyons, if not removed
during grading, is potentially significant.
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4.0 RECOMMENDATIONS
4.1 Earthwork
We anticipate that earthwork during the mass grading operations at the site will consist of site
preparation, removals of unsuitable soil, excavation of cut material, fill placement, and trench
excavation and backfill. We recommend that earthwork on-site be performed in accordance with the
following recommendations, the City of Carlsbad grading requirements, and the General Earthwork
and Grading Specifications for Rough-Grading (GEGS) included in Appendix D. In case of
conflict, the following recommendations shall supersede those included as part of Appendix D.
4.1.1 Site Preparation
Prior to the grading of areas to receive structural fill or engineered stractures, the areas
should be cleared of surface obstractions, any existing debris, unsuitable material (such as
desiccated documented fill soils, undocumented fill soils, topsoil, colluvium, alluvium,
landslide deposits, and weathered formational materials) and stripped of vegetation.
Vegetation and debris should be removed and properly disposed of off-site. Holes resuhing
from the removal of buried obstructions that extend below finished 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 6 to 12 inches, brought to an
above-optimum moisture condition, and recompacted to at least 90 percent relative
compaction (based on American Standard of Testing and Materials [ASTM] Test Method
D1557).
4.1.2 Removal and Recompaction of Unsuitable Soils
As discussed in Sections 2.2 and 3.0, portions of the site are underlain by unsuitable soils,
which may settle under the surcharge of fill and/or foundation loads. These materials
include desiccated documented fill soils, undocumented fill soils, topsoil, colluvium,
alluvium, landslide deposits and weathered formational material. Compressible materials
not removed by the planned grading should be excavated to competent material, moisture
conditioned or dried back (as needed) to obtain an above-optimum moisture content, and
then recompacted prior to additional fill placement or surface improvements. The actual
depth and extent of the required removals should be determined during grading operations
by the geotechnical consultant; however, estimated removal depths are summarized below.
1) Existing Documented Fill
The desiccated upper portion of the existing documented fills located in the eastem
and southeastem portions of the site (associated with the grading of Carrillo Ranch)
should be removed to competent fill prior to placement of additional fill. These
materials can be utilized as fill materials provided they are moisture conditioned and
free of deleterious materials. The estimated removal depths of the desiccated
documented fills are anticipated to be on the order of 1 to 5 feet. However, deeper
removals may be required along the edges of the fill where left-in-place unsuitable
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soils may be present below the 1:1 (horizontal to vertical) removal edge extending
from the existing toe-of-slope down undemeath the fill.
2) Existing Undocumented Fill
The existing undocumented fills should be completely removed prior to placement of
additional fill. These materials can be utilized as fill materials provided they are
moisture conditioned and free of deleterious materials. The estimated removal depths
of the undocumented fill soils range from 1 to more than 25 feet in depth. All trash,
constraction debris, and decomposable material should be removed and disposed of
off-site.
3) Topsoil
Areas to receive fill which are on slopes flatter than 5:1 (horizontal to vertical) and
where normal benching would not completely removed the topsoil, should be stripped
to suitable formational material prior to fill placement. Topsoil is expected to be
generally 1 to 4 feet thick, although localized deeper accumulations may be
encountered during grading.
4) Alluvium and Colluvium
In cut and fill areas, colluvial and alluvial materials should be completely removed to
competent material. Where the alluvium/colluvium is located above the water table,
this will most likely entail complete removal of these materials to competent bedrock.
In areas where a shallow water table prevents the removal of these materials using
conventional earthmoving equipment, (i.e. scrapers), we recommend the remaining
material be removed by top loading (wet removal) or be surcharged and drained with
wick drains. At the present time, we recommend further investigation of the areas
where shallow ground water is present within the alluvial soils in order to determine
the compressibility characteristics of the alluvial soils. Based on the results of the
additional evaluation, specific geotechnical recommendations can be provided
conceming the mitigation of the deep saturated alluvium and fill soils placed in these
areas.
5) Landslide Deposits
The landslide deposits within the limits of the planned grading should be removed to
competent material during site grading in order to remove the highly disturbed and
weathered material. The actual depth of stripping or overexcavation should be
determined during grading based on field observations by the geotechnical consuhant.
However, preliminary recommendations relative to the removals of the landslides are
presented on Table 1 for each of the mapped landslides on the site. Additional and/or
specific recommendations may be made during the grading plan review after the
completion of more detailed grading plans are developed.
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4.1.3 Excavations
Excavations of the on-site sedimentary and surficial materials may generally be
accomplished with conventional heavy-duty earthwork equipment. Localized cemented
zones in the Santiago Formation may be encountered that may require heavy ripping. All
oversized rock that is encountered should be placed as fill in accordance with the
recommendations presented Appendix D.
4.1.4 Cut/Fill Transition Conditions
In order to reduce the potential for differential settlement in areas of cut/fill transitions, we
recommend the entire cut portion of the transition building pads be overexcavated and
replaced with properly compacted fill to mitigate the transition condition beneath the
proposed stmcture. For transitions less steep than a 2:1 (horizontal to vertical), the
overexcavation of the cut portion of the building pad should be a minimum of 4 feet below
the planned finish grade elevation of the pad. For cut/fill transitions steeper than a 2:1
(horizontal to vertical) and for transitions beneath multi-unit and large commercial
stractures, site specific overexcavation recommendations should be made after the final
grading and development plans are completed. All overexcavations should extend laterally
at least 10 feet beyond the building perimeter or footprint.
4.1.5 Fill Placement and Compaction
The on-site soils are generally suitable for use as compacted fill provided they are free of
organic material, trash or debris, and rock fragments larger than 8 inches in maximum
dimension. All fill soils should be brought to above-optimum moisture conditions 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 the current City of Carlsbad grading ordinances, sound constraction
practices, and the General Earthwork and Grading Specifications of Rough-Grading
presented in Appendix D.
4.1.6 Settlement of Deep Fills
Subsequent to removals of compressible soils, fills of up to approximately 70 to 80 feet in
thickness are planned on the site. Our experience and analysis indicates that potential
settlement in these deep fill areas maybe on the order of 10 inches (depending on
compactive effort) and may take as long as 6 months (or longer) to occur. Most of this
settlement is anticipated to occur during grading. We anticipate that post constraction
settlement of onsite fills to be on the order of a maximum of 3 inches. Release of building
pad areas for constraction of stractures in fill areas deeper than 50 feet should be made
based on the results of surface settlement monuments placed at the completion of grading.
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Provisional information indicates the release of building pads for construction in areas not
underlain by saturated alluvium will be on the order of 3 months following grading.
4.1.7 Expansive Soils and Selective Grading
The laboratory test results and our professional experience with similar materials on sites in
the vicinity indicate that the on-site soils possess a very low to very high expansion
potential. As a result, the presence of highly expansive materials within 5 vertical feet from
finish grade will require special foundation and slab considerations (i.e. the use of a post-
tension foundation system). In general, this condition should be limited to finish grade pads
comprised of Santiago Formation claystone or sihstone (generally below an approximate
elevation of 270 to 300 feet msl across the site) or where these materials are utilized as
compacted fill within 5 feet of finish grade.
As an altemative to the use of a post-tension foundation system on lots possessing a
medium to very high expansion potential, the building pads may be overexcavated a
minimum of 5 feet below finish pad grade and replace with properly compacted fill
possessing very low to low expansion potential (i.e., the sandy soil of the Santiago
Formation present in the higher elevations of the site. Should this altemative be chosen, the
overexcavation should extend across the entire lot and be graded such that water does not
accumulate beneath the stractures (by providing a minimum 2 percent fall of the
overexcavation bottom towards the street or existing fill).
4.2 Slope Stabilitv
Review ofthe 200-scale tentative tract map/grading plans (PDC, 2001b), indicates that cut and fill
slopes will be constracted to maximum heights on the order of 50 and 70 feet, respectively. We
understand that these finished slopes are planned at inclinations of 2:1 (horizontal to vertical) or
flatter. Based on the resuhs of our investigation and geologic interpretations, the proposed slopes
were analyzed for gross stability utilizing the STABL slope stability program and surficial stability
using the infinite slope equation with steady-state seepage. The parameters utilized in our slope
stability analysis are based on our laboratory testing, our experience with similar soil types, and our
professional judgment. The parameters utilized in the slope stability analysis are presented on Table
3. A summary of our slope stability analyses is presented below.
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Table 3
Slope Stability Soil Parameters
Material
Moist Unit
Weight
(pcf)
Saturated
Unit Weight
(pcf)
Friction
Angle
(degrees)
Cohesion
(psf)
Artificial Fill Soils 125 130 25 200
Quatemary Alluvium 125 130 18 100
Landslide Material 125 130 18 100
Clay Seam/Rupture
Surface
120 125 8 100
Santiago Formation
(sandstone) 130 135 30 300
Santiago Formation
(claystone along bedding) 130 135 13.5 100
Santiago Formation
(claystone across bedding) 130 135 30 300
4.2.1 Deep-Seated Stabilitv
1) Fill Slopes
The materials anticipated for use in fill slope grading will predominantly consist of
sandy and silty to clayey soils of the Santiago Formation. Our analysis, assuming
homogeneous slope conditions, indicates the anticipated fill slopes up to the
maximum proposed heights of 70 feet will have a calculated factor of safety of 1.5 or
greater with respect to potential, deep-seated failure. The proposed slopes should be
constracted in accordance with the recommendations of this report, the attached
General Earthwork and Grading Specifications for Rough-grading (Appendix D), and
City of Carlsbad grading code requirements.
2) Cut Slopes/Landslide Stabilization
Engineering analysis of the proposed 2:1 (horizontal to vertical) cut slopes up to a
maximum height of approximately 50 feet indicates the deep-seated stability of the
slopes, in general, are stable from a geotechnical standpoint provided adverse geologic
conditions are not present. The results of our stability analysis indicate that proposed
cut slopes have a static factor of safety in excess of 1.5 for gross stability after
remedial grading is performed (i.e. the constraction of buttresses) and our
geotechnical recommendations are adhered to.
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However, cut slopes consisting of Santiago Formation claystones and siltstones may
be surficially unstable and may require the constraction of stability or replacement
fills on the slopes. Based on our subsurface exploration (Appendix B), we anticipate
that the majority of the cut slopes below an approximate elevation of 270 to 300 feet
msl will consist of Santiago Formation claystones and siltstones. The stability fill keys
should be constructed a minimum of 15 feet wide, at least 5 feet below the toe-of-
slope grade, and have a minimum 2 percent into-the-slope inclination. The
approximate locations of the stability fill keys are presented on the Remedial Grading
Map (Plate 2). A typical detail for stability fill constraction is provided in the attached
General Earthwork and Grading Specifications (Appendix D).
In addition, Geologic Cross-Sections A-A' through M-M' (Figures 4 through 17) were
prepared in areas of landslides to further evaluate slope stability and to provide
buttress designs, where appropriate, to increase the overall slope static factor-of-safety
to at least a 1.5. Where buttresses are recommended, the preliminary dimensions are
presented on the appropriate cross-section. A summary of the landslides is presented
on Table 1. Prior to constraction of the recommended buttresses presented herein, the
provisional stability recommendations should be reviewed and additional buttress
design analysis performed based on the actual design grading plans.
We recommend the geotechnical consultant document and geologically map all
excavations including cut slopes during grading. The purpose of this mapping is to
substantiate the geologic conditions assumed in our analyses. Additional investigation
and stability analysis may be required if unanticipated or adverse conditions are
encountered during site development.
3) Slope Face Compaction and Finishing
Due to the high expansion potential of the claystones and siltstones within the
Santiago Formation, special compaction procedures will be necessary in order for the
specified compaction to be achieved out to the slope face. Soils placed within 15 feet
of the face of slope should consist of a mixture of clay and sand. The sole use of
highly expansive clayey or clean sandy material within 15 feet of the face of slope
should be avoided. Overbuilding the slope faces a minimum of 5 feet and trimming
them back or frequent back-rolling with sheepsfoot compactors (at 1-to 3-foot vertical
intervals) and back-rolling the completed slope with a short-shank sheepsfoot may be
utilized to achieve the specified compaction of the slope face.
4) Stabilitv for Temporary Backcut Slopes During Grading
The temporary backcut slopes that will be created during removal of unsuitable
materials or constraction of the buttress and/or stabilization fills should have
acceptable temporary factors of safety during grading. However, since there is still a
small risk of slope instability, the possibility of temporary cut slopes failures may be
reduced by: 1) keeping the time between cutting and filling operations to a minimum;
2) limiting the maximum length of back cut slopes exposed at any one time; 3) making
removals at the head of the landslide before performing the buttress backcut near the
toe of the landslide; and 4) cutting the temporary slopes at slope inclinations no
steeper than 1-1/2:1 (horizontal to vertical) in locations of adverse geologic conditions
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and 1:1 (horizontal to vertical) inclinations in other locations. In critical areas, we may
recommend a contractor's representative observe the backcut for signs of instability
during buttress constraction. Backcut safety is the responsibility of the contractor.
It is of utmost importance to schedule the earthwork sequence such that the time
between removal and recompaction is reduced to a minimum. Full-time geologic
inspection should be performed during backcut excavation, not only to confirm the
geologic conditions but also to provide early waming of incipient failure of the
temporary excavations and to allow in-constraction reaction to accommodate such
failures and keep their occurrence to a minimum.
4.2.2 Surficial Stabilitv
Surficial stability of the 2:1 (or flatter) fill and cut slopes were evaluated during our
supplemental investigation. Our calculations indicate a factor of safety in excess of 1.5 for
surficial stability under 4-foot steady state seepage. However, due to the presence of
potentially adverse geologic conditions, we have recommended stability fills along the
slopes exposing Santiago Formation claystones or sihstones as discussed in Section 4.2.1,
Part 2.
4.3 Control of Ground Water and Surface Waters
Based on our preliminary and supplemental geotechnical investigations, it is our opinion that a
permanent shallow ground water table does not currently exist at the site. However, a perched
ground water condition is present within the alluvial soils in the main drainages of the property. The
control of ground water in a hillside development is essential in order to reduce the potential for
undesirable surface flow, hydrostatic pressure and the adverse effects of ground water on slope
stability.
We recommend that measures be taken to properly finish grade the site such that drainage water is
directed away from top-of-slopes and away from proposed structures. No ponding of water should
be permitted. Drainage design is within the purview of the design civil engineer.
Even with these provisions, our experience indicates that shallow ground water/perched ground
water conditions can develop in areas where no such ground water conditions existed prior to site
development, especially in areas where a substantial increase in surface water infiltration results
from landscape irrigation. We recommend that an engineering geologist be present during grading
operations to observe and record possible future seepage areas and provide field recommendations
for mitigation of fiiture potential seepage.
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4.3.1 Canvon Subdrains
In order to help reduce the potential for ground water accumulation in the proposed fill
areas, we recommend subdrains be installed in the bottoms of canyons fill areas (or on the
sides of the removal if saturated alluvium is left-in-place) prior to fill placement. The
canyon subdrains should consist of a 6-inch diameter PVC pipe surrounded by a minimum
of 9-cubic feet (per linear foot) of 3/4-inch gravel wrapped in a filter fabric (Mirafi HON or
equivalent). Where the subdrain is placed on fill in order to outlet the subdrain, the
subdrain should consist of solid PVC pipe. The subdrain should have a minimum fall of at
least 1 percent.
Specific subdrain recommendations will be made upon our review of the final site grading
plans. However, preliminary canyon subdrain locations are presented on the Remedial
Grading Map (Plate 2). Details for subdrain constraction are provided in the attached
General Earthwork and Grading Specifications (Appendix D). The actual need and/or
location of canyon subdrains should be based on the evaluation of the configuration of the
canyon bottoms by the geotechnical consultant after the removal of compressible soils have
been completed.
A representative of the project civil engineer should survey the installed subdrains for
alignment and grade. Sufficient time should be allowed for the surveys prior to
commencement of fill placement operations over the subdrain. The subdrain outlets should
be installed to discharge water into positive drainage devices (e.g. storm drain boxes,
natural canyon bottoms, etc.).
4.3.2 Buttress and Stabilitv Fill Subdrains
Subdrains should be provided in the buttress and stability fills constracted on-site in order
to minimize slope instability. The subdrains should be placed along the heel of the buttress
or stability fill key (across the entire length of the key) and along the backcut at
approximately 30-foot vertical intervals. The subdrains should be placed and constracted in
accordance with the recommendations presented in Appendix D.
4.3.3 Cut Slope Seepage Conditions
Due to the anticipated presence of relatively permeable soils (i.e. Santiago Formation
sandstone) underlain by relatively impermeable formational claystone or sihstones exposed
in cut slopes on the site, groundwater seepage conditions are likely at these contacts. Slopes
exposing these conditions (especially when the area at the top of the slope will be irrigated
and/or where stractures will be located at the toe-of-slope) should be evaluated by the
geotechnical consultant to determine if some type of subdrain system should be placed to
intercept the groundwater seepage. Recommendations to mitigate the seepage conditions
include installing a toe-of-slope subdrain system, installing a subdrain system at or slightly
below the contact between the permeable and impermeable materials or by replacing the
slope with a stability fill (discussed in Section 4.2.1, Part 2).
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4.4 Settlement Monitoring
We recommend that fills greater than 50 feet in depth or where alluvium is left in place beneath the
fill be monitored (by the placement of settlement monuments upon completion of rough-grading
and periodic surveying). The number of settlement monuments necessary for monitoring and their
placement locations should be determined following a review of the site grading plans by the
project geotechnical consultant. Constraction of settlement-sensitive stractures in these deep fill
areas should be postponed until anticipated settlement is within tolerable limits based on the
analysis of the geotechnical consultant.
4.5 Surface Drainage and Lot Maintenance
Positive drainage of surface water away from stractures 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 ftirther 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.
Property owners should be reminded of the responsibilities of hillside maintenance practices (i.e.,
the maintenance of proper lot drainage; the undertaking of property improvements in accordance
with sound engineering practices; and the proper maintenance of vegetation, including pradent lot
and slope irrigation).
4.6 Graded Slopes
It is recommended that all graded slopes within the development be planted with drought-tolerant
ground cover vegetation as soon as practical to protect against erosion by reducing ranoff velocity.
Deep-rooted vegetation should also be established to protect against surficial slumping.
Oversteepening of existing slopes should be avoided during fine grading and constraction unless
supported by appropriately designed retaining stractures.
We recommend terrace drains on the slopes be designed by the civil engineer and be constracted in
accordance with current City of Carlsbad specifications. Design of surface drainage provisions are
within the purview of the project civil engineer.
•23 -
Leighton
971009-005
4.7 Plan Review and Construction Observation
The provisional recommendations contained in this report must be confirmed once the actual
grading plans are available. At that time, additional investigation and analysis maybe required.
Construction observation of all on-site excavations and field density testing of all compacted fill
should be performed by a representative of this office. We recommend that a geologist map all
excavations during grading for the presence of potentially adverse geologic conditions. All
footing excavations should be reviewed by this office prior to placing steel or concrete.
•24-
Leighton
971009-005
5.0 LIMITATIONS
The conclusions and recommendations in this report are based in part upon data that were obtained from
a limited number of observations, site visits, excavations, samples, and tests. Such information is by
necessity incomplete. The nature of many sites is such that differing geotechnical or geological
conditions can occur within small distances and under varying climatic conditions. Changes in
subsurface conditions can and do occur over time. Therefore, the findings, conclusions, and
recommendations presented in this report can be relied upon only if Leighton and Associates has the
opportunity to observe the subsurface conditions during grading and construction of the project, in order
to confirm that our preliminary findings are representative for the site.
4 -25-
Leighton
Table 1
Geotechnical Summary of Existing Landslides
971009-005
Landslide
Reference
Number
Location Geologic Conditions Conclusions and Recommendations
1 Eastem portion of PA-1
Landslide is a relatively large surficial slump. The
landslide appears to have moved as a relatively
incoherent mass of material. Failure was probably
related to saturation conditions at the base of the
weathered zone in the formational material (based on
evidence of ground water seepage zones observed in the
area). The backscarp was identified in Exploratory
Trench T-27. The thickness of landslide is unknown, but
anticipated to be on the order of 10 to 15 feet.
A buttress approximately 60 feet wide with a depth ofat
least 10 feet below the proposed toe-of-slope is
recommended to remove the landslide and stabilize the
slope. A subdrain system at the heel of the key and panel
drains in areas of observed and/or potential ground
water seepage zones should also be anticipated.
2
Southeastem portion of
PA-2
(Cross-Section E-E')
Landslide is essentially the same as Landslide No. 1 (i.e.
a relatively large surficial slump). The landslide appears
to have moved as a relatively incoherent mass of
material. Failure was probably related to saturation
conditions of the weathered zone based on evidence of
ground water seepage zones observed in the area. The
basal slip surface was reportedly encountered in
Exploratory Trench GT-42 at a depth of 8 feet below the
ground surface.
Complete removal of the relatively large surficial slump
to competent formational material within the limits of
grading is recommended. The removal depth is
estimated to be on the order of 10 to 15 feet. In addition,
it should be anticipated that the proposed fill slope near
the bottom of the landslide will require a buttress
approximately 40 feet wide with a depth of at least 15
feet below the proposed toe-of-slope. A subdrain system
including possible panel drains in areas of observed
and/or potential ground water seepage zones should be
anticipated.
3 North central portion of
OS-1
Landslide is a relatively large surficial slump. Landslide
appears to have moved as a relatively incoherent mass
of material. Failure was probably related to saturation
conditions based on evidence of ground water seepage
observed in the area. Thickness of landslide is unknown,
but anticipated to be on the order of 10 to 15 feet.
This landslide is outside the limits of the proposed
grading; and therefore, no remedial grading is needed.
However, we recommend that the fill slope key
excavation for the proposed fill slope west of this
landslide be geologically mapped to identify any
evidence that the landslide may encroach into the fill
slope key.
Table 1
Geotechnical Summary of Existing Landslides (continued)
971009-005
Landslide
Reference
Number
Location Geologic Conditions Conclusions and Recommendations
4 Southeast side of OS-1
Landslide is a relatively large surficial slump. Landslide
appears to have moved as a relatively incoherent mass
of material. Failure was probably related to saturation
conditions based on evidence of ground water seepage
observed in the area. Thickness of landsUde is unknown,
but anticipated to be on the order of 10 to 20 feet.
Complete removal of the relatively large surficial slump
to competent fonnational material within the limits of
grading is recommended. The removal depth is
estimated to be on the order of 10 to 20 feet. In addition,
it should be anticipated that the proposed fill slope
above the landsUde on the east side will require a fill
slope/shear key approximately 15 feet wide with a depth
of at least 5 feet below the proposed toe-of-slope.
5 East side of OS-1 and
West side of PA-10
Landslide is a relatively large surficial slump. LandsUde
appears to have moved as a relatively incoherent mass
of material. Failure was probably related to saturation
conditions based on evidence of ground water seepage
observed in the area. Thickness of landslide is unknown,
but anticipated to be on the order of 10 to 20 feet.
Complete removal of the relatively large surficial slump
to competent formational material is reconimended
since the landslide is completely within the limits of
grading. The removal depth is estimated to be on the
order of 10 to 20 feet. A subdrain system including
possible panel drains in areas of observed and/or
potential ground water seepage zones may be needed.
6
Southwest side of PA-6
and northwest side of PA-
IO
(Cross-Section D-D')
Landslide complex is a relatively large and deep block-
slide type landslide that may include more than one
landslide mass. The landslide complex appears to have
moved as at least two semi-competent blocks along a
north to northwest dipping rapture surface at an
approximate elevation of 265 feet. Based on Borings
LB-11 and LB-12, the upper approximately 25 feet of
the landslide mass was found to be potentially
compressible and unsuitable for the support of fill or
surface improvements.
Remove the potentially compressible soil to competent
landslide material in the upper portion of the landslide.
The removal depth is estimated to be on the order of 20
to 25 feet. The proposed in-filling of the canyon to the
northwest with compacted fill will effectively buttress
the landslide complex.
Table 1
Geotechnical Summary of Existing Landslides (continued)
971009-005
Landslide
Reference
Number
Location Geologic Conditions Conclusions and Recommendations
7
Northwestem portion of
PA-11
(Cross-Section M-M')
Landslide is assumed to be a moderately sized rotational
type landslide. The landslide appears to have moved as
a relatively coherent mass of material. Thickness of
landsUde is unknown, but anticipated to be on the order
of20to35 feet thick.
Constraction of a buttress on the order of 50 feet wide
with a depth of approximately 30 feet is recommended
along the proposed toe of the fill slope to completely
remove the landslide. A subdrain system in the buttress
is also recommended.
8 Westem portion of PA-11
Landslide is a moderately sized surficial slump.
Landslide appears to have moved as a relatively
coherent mass of material. Thickness of landsUde is
unknown, but anticipated to be on the order of 10 to 20
feet.
Complete removal of the relatively large surficial slump
to competent formational material within the limits of
grading is recommended. The removal depth is
estimated to be on the order of 10 to 20 feet. The
proposed fill slope on the west side of the landslide will
require a fill slope/shear key approximately 15 feet wide
and 5 feet deep below the toe-of-slope.
9
Southem portion of PA-11
and partially offsite to the
south
(Cross-Section L-L')
Landslide complex is a relatively large and deep block-
slide type landslide. The landslide likely faUed along a
clayseam or weak claystone bed at an elevation near the
bottom of the adjacent drainage to the southeast. The
landsUde is estimated to be up to approximately 60 feet
deep. It is not known how deep or the relative extent of
the graben area, which will be located beneath a
proposed fill slope. A second proposed fill slope is
located near the bottom of the landslide just north ofthe
property line.
Some type of buttress will be required to stabiUze the
landslide and provide an adequate factor of safety for
the proposed fill slopes. The estimated size of the
buttress at the toe of the landslide is 100 feet wide and
15 feet deep at the toe. A stability fill/shear key is also
recommended below the upper fill slope. This key
should be a minimum of 15 feet wide and 10 feet deep
below the proposed toe of slope. In addition, removal of
the unsuitable and potentially compressible portion of
the landslide is also reconimended. The estimated depth
of these removals is on the order of 10 to 20 feet within
the Umits of the proposed grading. Additional
investigation and analvsis are recommended to better
9
Southem portion of PA-11
and partially offsite to the
south
(Cross-Section L-L')
Landslide complex is a relatively large and deep block-
slide type landslide. The landslide likely faUed along a
clayseam or weak claystone bed at an elevation near the
bottom of the adjacent drainage to the southeast. The
landsUde is estimated to be up to approximately 60 feet
deep. It is not known how deep or the relative extent of
the graben area, which will be located beneath a
proposed fill slope. A second proposed fill slope is
located near the bottom of the landslide just north ofthe
property line.
defme the landslide geometrv and the buttress design.
Table 1
Geotechnical Summarv of Existing Landslides (continued)
971009-005
Landslide
Reference
Number
Location Geologic Conditions Conclusions and Reconunendations
9A
Southem portion of PA-11
and partially offsite to the
south
(Cross-Section K-K')
Landslide complex is a relatively small block-slide type
landslide. Based on Geocon Boring GLB-15 located
offsite, the landslide failed along a clayseam within the
Santiago Formation claystone at a depth of
approximately 13 feet below the ground surface (at an
approximate elevation of 237 feet). The landslide is
estimated to be up to approximately 25 to 30 feet deep.
A fill slope is proposed on the upper portion of the
landsUde. A proposed cut slope on the off-site property
will be made through the front of the landslide.
Constraction of a buttress on the order of 60 feet wide
with a depth of approximately 25 feet (or through the
landslide rapture surface) is recommended along the
proposed toe of the fill slope located north of the
property line. In addition removal of the upper
approximately 5 to 10 feet of the landslide mass to
competent material is also recommended. A subdrain
system in the buttress is also reconimended.
10 Southeastem comer of
PA-11
(Cross-Section I-I')
Landslide is a relatively small block-slide type landslide.
The landslide rapture surface was encountered in Boring
LB-27 at an approximate depth of 16 feet below the
ground surface (at an approximate elevation of 220
feet). It appears that the landslide failed along a weak
clay bed within the Santiago Formation claystone. The
landsUde is estimated to be up to approximately 25 to 30
feet deep. A fill slope is proposed on the lower portion
of the landslide north of the property line.
Constraction of a buttress on the order of 60 feet wide
with a depth of approximately 10 feet (or through the
landslide rapture surface) is recommended along the
proposed toe of the fill slope located north of the
property line. In addition removal of the upper
approximately 5 to 10 feet of the landslide mass to
competent material is also recommended. A subdrain
system in the butfress is also recommended.
11
Southem portion of PA-8
and southeastem comer of
PA-11
(Cross-Section H-H')
Landslide is similar to Landslide No. 10 (i.e. a relatively
small surficial slump). The landslide rupture surface was
encountered in Boring LB-26 at a depth of
approximately 25 feet below the ground surface (at an
approximate elevation of 220 feet). It appears that the
landslide failed along a weak clay bed within the
Santiago Formation claystone. The landslide is
estimated to be up to approximately 25 to 30 feet deep.
A proposed fill slope is proposed on the lower portion
of the landslide north of the property line.
Constraction of a buttress on the order of 60 feet wide
with a depth of approximately 10 feet (or through the
landslide rapture surface) is reconimended along the
proposed toe of the fill slope located north of the
property line. In addition removal of the upper
approximately 5 to 10 feet of the landslide mass to
competent material is also recommended. A subdrain
system in the butfress is also reconimended.
Table 1
Geotechnical Summarv of Existing Landslides (continued)
971009-005
Landslide
Reference
Number
Location Geologic Conditions Conclusions and Recommendations
12
Southem portion of PA-8,
southeastem portion of
PA-11, and westem
portion of PA-12
(Cross-Sections C-C and
G-G')
Landslide is relatively large and extends partially off-
site to the south. The landslide appears to have moved
as a semi-competent block on a rapture surface that is
dipping approximately 5 degrees to the southeast. The
landslide is estimated to be up to approximately 30 to 50
feet deep. The lower end of the landslide is likely buried
by recent alluvium/colluvium.
Based on the current proposed grades of PA-12, the fill
on and in front of the lower portion of the landslide
effectively butfresses the landsUde, and therefore, no
butfress key is required. However, the unsuitable and
potentially compressible portion of the landslide should
be removed to competent material. Removal depths of
the unsuitable material are estimated to be on the order
of 20 to 30 feet deep.
13
Northwestem portion of
PA-12 and the southem
portion of OS-3
(Cross-Section F-F')
Landslide is relatively large and extends partially into an
open space area (OS-3). The landslide appears to have
moved as a semi-competent block on a relatively flat
rapture surface. The landslide rapture surface was
encountered in Boring LB-7 at a depth of approximately
32.5 feet below the ground surface (at an approximate
elevation of275 feet). It appears that the landsUde failed
along a weak clay bed within the Santiago Formation
claystone just above a sandstone unit. The landslide is
estimated to be approximately 35 to 80 feet thick.
Some type of butfress will be required to stabilize the
landslide. However, based on the current proposed
grades, unknown geometry of the upper portion of the
landslide, and our understanding that grading cannot
occur within the open space area dictates that a butfress
cannot be designed within the current parameters. An
additional mvestigation and analvsis are reconimended
13
Northwestem portion of
PA-12 and the southem
portion of OS-3
(Cross-Section F-F')
Landslide is relatively large and extends partially into an
open space area (OS-3). The landslide appears to have
moved as a semi-competent block on a relatively flat
rapture surface. The landslide rapture surface was
encountered in Boring LB-7 at a depth of approximately
32.5 feet below the ground surface (at an approximate
elevation of275 feet). It appears that the landsUde failed
along a weak clay bed within the Santiago Formation
claystone just above a sandstone unit. The landslide is
estimated to be approximately 35 to 80 feet thick.
to better define the landslide geometrv and the butfress
13
Northwestem portion of
PA-12 and the southem
portion of OS-3
(Cross-Section F-F')
Landslide is relatively large and extends partially into an
open space area (OS-3). The landslide appears to have
moved as a semi-competent block on a relatively flat
rapture surface. The landslide rapture surface was
encountered in Boring LB-7 at a depth of approximately
32.5 feet below the ground surface (at an approximate
elevation of275 feet). It appears that the landsUde failed
along a weak clay bed within the Santiago Formation
claystone just above a sandstone unit. The landslide is
estimated to be approximately 35 to 80 feet thick.
design and/or design grades in front of the landslide
13
Northwestem portion of
PA-12 and the southem
portion of OS-3
(Cross-Section F-F')
Landslide is relatively large and extends partially into an
open space area (OS-3). The landslide appears to have
moved as a semi-competent block on a relatively flat
rapture surface. The landslide rapture surface was
encountered in Boring LB-7 at a depth of approximately
32.5 feet below the ground surface (at an approximate
elevation of275 feet). It appears that the landsUde failed
along a weak clay bed within the Santiago Formation
claystone just above a sandstone unit. The landslide is
estimated to be approximately 35 to 80 feet thick. need to be raised in order stabilize the landslide.
14 Southem portion of PA-13
Landslide is a relatively smaU block-slide type landslide.
The landslide rapture surface is anticipated to be at the
same approximate elevation as Landslide 15 (i.e.
approximately 190 feet) within a clayey siltstone bed of
the Santiago Formation. The landslide is estimated to be
up to approximately 25 to 30 feet deep. The lower end
of the landslide is likely buried by recent
alluvium/colluvium.
Removal the potentially compressible soil to competent
landslide material in the upper portion of the landsUde is
recommended. The removal depth is estimated to be on
the order of 10 to 15 feet. The proposed m-filling ofthe
canyon to the west will effectively butfress the landslide.
In addition, it should be anticipated that the upper end of
the landsUde will need to be completely removed to
competent fonnational material outside the proposed
grading limits in order to stabiUze the natural slope. A
key approximately 15 feet wide should be constracted in
this area. As an altemative, a building setback from the
landslide may be provided.
Table 1 971009-005
Geotechnical Summarv of Existing Landslides (continued)
Landslide
Reference
Number
Location Geologic Conditions Conclusions and Recommendations
15 Southem portion of PA-13
(Cross-Section J-J')
Landslide is essentially the same as Landslide No. 14
(i.e. a relatively small block-slide type landslide). The
landsUde rapture surface was encountered in Boring
LB-6 at an approxmiate depth of 26 feet below the
ground surface (at an approximate elevation of 190
feet). It appears that the landsUde failed along clayey
siltstone bed directly below a cemented zone within the
Santiago Formation. The landslide is estimated to be up
to approximately 25 to 30 feet deep. The lower end of
the landsUde is likely buried by recent
alluvium/colluvium.
Removal the potentially compressible soil to competent
landslide material in the upper portion of the landslide is
reconimended. The removal depth is estimated to be on
the order of 10 to 15 feet. The proposed in-filling of the
canyon to the west with compacted fill will effectively
buttress the landslide. In addition, it should be
anticipated that the upper end of the landslide will need
to be completely removed to competent formational
material outside the proposed grading limits in order to
stabilize the natural slope above the proposed relatively
flat building pad. A key approximately 15 feet wide
should be constracted in this area.
16 Northem portion of PA-13
Landslide is a relatively small block-slide type landslide.
The landslide rapture surface was encountered in Boring
LB-14 at an approximate depth of 34 feet below the
ground surface (at an approximate elevation of 200 feet)
near the top of a claystone bed within the Santiago
Formation. The landslide is estimated to be up to
approximately 35 to 40 feet deep. The lower end of the
landslide is likely buried by recent alluvium/colluvium.
Removal the potentially compressible soil to competent
landslide material in the upper portion of the landslide is
recommended. The removal depth is estimated to be on
the order of 10 to 15 feet. The proposed in-filling of the
canyon to the west with compacted fill will effectively
butfress the landsUde.
17 Northem portion of PA-13
Landslide is essentially the same as LandsUde No. 16
(i.e. a relatively small block-slide type landslide). The
landslide rapture surface is anticipated to be at the same
approximate elevation as Landslide 16 (i.e.
approximately 200 feet) within a clayey siltstone bed of
the Santiago Fonnation. The landsUde is estimated to be
up to approximately 25 to 30 feet deep. The lower end
of the landslide is likely buried by recent
alluvium/colluvium.
Removal the potentially compressible soil to competent
landslide material in the upper portion of the landslide is
reconimended. The removal depth is estimated to be on
the order of 10 to 15 feet. The proposed in-filling of the
canyon to the west with compacted fill will effectively
buttress the landslide.
Table 1
Geotechnical Summarv of Existing Landslides (continued)
971009-005
Landslide
Reference
Number
Location Geologic Conditions Conclusions and Recommendations
18 OS-3 and OS-7? And
northwest portion of PA-
13
Landslide is a moderately sized surficial slump.
Landslide appears to have moved as a relatively
coherent mass of material. Thickness of landslide is
unknown, but anticipated to be on the order of 10 to 20
feet.
Complete removal of the relatively large surficial slump
to competent formational material within the limits of
grading is reconimended. A building setback may be
required adjacent to the landslide (due to the unstable
landslide in the open space/natural slope above the
building pad to the west). As an altemative, grading in
the open space may be performed to stabilize the upper
portion ofthe landslide outside the limits of grading.
19
OS-3 and OS-7? And
northwest portion of PA-
13
(Cross-Section A-A')
LandsUde is a moderately sized block-slide type
landslide. The landslide appears to have moved as a
semi-competent block on a rapture surface that is
dipping approximately 10 to 12 degrees to the east. The
landslide rapture surface was encountered in Boring
LB-20 at an approximate depth of 18 feet below the
ground surface (at an approximate elevation of 242 feet)
within a weak claystone bed in the Santiago Formation.
The landslide is estimated to be up to approximately 20
to 25 feet deep. The lower end of the landslide is likely
buried by recent alluvium/colluvium.
The proposed in-filling of the canyon to the west with
compacted fill will effectively butfress the landslide.
However, the landslide should be removed to competent
fonnational material from a 1:1 projection down and
away from the limits of fill.
20a and 20b OS-4
Landslide complex appears to be a relatively large
block-slide type landslide completely located in an open
space area.
Since the landslide is completely within an open space
area, no remedial grading is required.
21aand21b OS-4
Landslide complex appears to be a relatively large
block-slide type landslide completely located in an open
space area.
Since the landslide is completely within an open space
area, no remedial grading is required.
Table 1
Geotechnical Summarv of Existing Landslides (continued)
971009-005
Landslide
Reference
Number
Location Geologic Conditions Conclusions and Recommendations
22 OS-4 Landslide complex appears to be a relatively large
block-slide type landslide completely located in an open
space area.
Since the landslide is completely within an open space
area, no remedial grading is requfred.
23 OS-2?
Landslide is a small surficial slump. The landslide
appears to have moved as a relatively incoherent mass
of material. The thickness of the slide is unknown but
beUeved to be on the order of 5 to 15 feet thick.
Complete removal of the small surficial slump to
competent fonnational material since the landslide is
completely within the limits of grading. The removal
depth is estimated to be on the order of 5 to 15 feet.
24 PA-3
Landslide is a small surficial slump in saturated
colluvium behind an earthen embankment. Completely remove the small surficial slump along with
the colluvium. Extend the canyon subdrain through this
area.
971009-005
APPENDIXA
References
Blake, Thomas F., 1996, EQFAULT, Version 2.2.
, 1998, FRISKSP.
Eisenberg, L.I., 1985, Pleistocene Faults and Marine Terraces, Northem San Diego County in Abbott, P.L.,
Editor, On the Manner of Deposition of the Eocene Strata in Northem San Diego County,
San Diego Association of Geologists, Field Trip Guidebook, pp. 86-91.
Eisenberg, L.I. and Abbott, P.L., 1985, Eocene Lithofacies and Geologic History, Northem SanDiego
County in Abbott, P.L., ed., On the Manner of Deposition of the Eocene Strata in Northem
San Diego County: San Diego Association of Geologists, Field Trip Guidebook, pp. 19-35.
Geocon, Inc., 1982a, Soil and Geologic Reconnaissance, Bressi Ranch, San Diego County, Califomia, File
No. D-2714-TOl, dated March 23, 1982.
, 1982b, Report of Phase I Geotechnical Study, Bressi Ranch, Carlsbad, Califomia, File No. D-
2714-T02, dated June 4, 1982.
, 1992, Preliminary Geotechnical Investigation, Rancho Carrillo, Villages E, J, and K, Carlsbad,
Califomia, Project No. 04787-12-04, dated December 30, 1992.
, 1993, Geologic Investigation for Rancho Carrillo Project - Major Roads, Carlsbad, Califomia,
ProjectNo. 04787-12-01, dated January 15, 1993.
, 1996, Geologic Investigation, Rancho Carrillo - El Fuerte Detention Basin Embankment and
Existing Bressi Dam, Carlsbad, Califomia, Project No. 04787-12-11, dated November
25, 1996.
, 1998, Final Report of Testing and Observation Services During Site Grading, El Fuerte
Detention Embankment, Rancho Carrillo, Carlsbad, Califomia, ProjectNo. 05845-12-07,
dated November 20, 1998.
, 2000, Supplemental Soil and Geologic Investigation, Villages of La Costa - The Greens,
Carlsbad, California, Project No. 06403-12-01, dated March 24, 2000.
Hannan, D., 1975, Faulting in the Oceanside, Carlsbad and Vista Areas, Northem San Diego County,
Califomia in Ross, A. and Dowlens, R.J., eds.. Studies on the Geology of Camp Pendleton
and Westem San Diego County, Califomia: San Diego Association of Geologists, pp. 56-
59.
Hart, E.W., 1997, Fault-Rupture Hazard Zones in Califomia, Alquist-Priolo Special Studies Zones Act of
1972 with Index to Special Studies Zones Maps: Department of Conservation, Division of
Mines and Geology, Special Publication42.
971009-005
1
APPENDIX A (continued)
Intemational Conference of Building Officials (ICBO), 1997, Uniform Building Code, Volume I -
Administrative, Fire- and Life-Safety, and Field Inspection Provisions, Volume II -
Stractural Engineering Design Provisions, and Volume III - Material, Testing and
Installation Provision, ICBO.
Jennings, C.W., 1994, Fault Activity Map of Califomia and Adjacent Areas; Califomia Division of Mines
and Geology, Geologic Data Map 6, Scale 1:750,000.
Leighton and Associates, Inc., 1992, City of Carlsbad, Geotechnical Hazards Analysis and Mapping Study,
84 Sheets, dated November, 1992.
, 1997, Preliminary Geotechnical Investigation, Bressi Ranch, Carlsbad, Califomia, Project No.
4971009-002, dated July 29,1997.
, 1998,Recommendations for Overexcavation of Potentially Compressible Materials, for Onsite
Portion of Land Outfall Sewer Relocation Project, Future Poinsettia Lane, Bressi Ranch,
Carlsbad, Califomia, ProjectNo. 4971009-002, dated March 26, 1998.
, 2000a, Geotechnical Review of Conceptual Grading Plans for the Wetland Restoration Area,
Bressi Ranch, Carlsbad, Califomia, Project No. 4971009-005, dated January 25, 2000.
, 2000a, Geotechnical Review of Land-Use Plans for Bressi Ranch, Carlsbad, Califomia,
ProjectNo. 4971009-005,dated March 2,2000.
, 2000c, Wetland Restoration Area Grading, Bressi Ranch, Carlsbad, Califomia, Project No.
4971009-005, dated April 17, 2000.
, 2000d, Remedial Quantity Estimates, Offsite Portion of Proposed Poinsettia Lane, Bressi Ranch
Development,Carlsbad, Califomia, ProjectNo. 971009-005, dated August 25,2000.
, 2001, Geotechnical Feasibility Study, Offsite Poinsettia Lane, Alicante Road and Borrow Sites
Within The Greens of The Villages of La Costa, Bressi Ranch Development, Carlsbad,
Califomia, ProjectNo. 971009-005, dated Januarys, 2001.
, Undated, Unpublished In-House Geotechnical Data.
Lindvall, S.C, and Rockwell, T.K., 1995, Holocene Activity of the Rose Canyon Fault Zone in San Diego,
Califomia: Joumal of Geophysical Research, V. 100,No. B12, p. 24, 124-24,132.
PDC, 2001a, Cut/Fill Exhibit, 200 Scale, Bressi Ranch, Carlsbad, Califomia, dated February 14,2001.
PDC, 2001b, Tentative Tract Map/Grading Plan, 200 Scale, Bressi Ranch, Carlsbad, Califomia, undated,
received February 16,2001.
A-2
971009-005
APPENDIX A (continued)
Reichle, M.S., and Kahle, J.E., 1990, Planning Scenario for a Major Earthquake, San Diego-Tijuana
Metropolitan Area: Califomia Division of Mines and Geology, Special Publication 100
180 p.
Rockwell, T.K., and Lindvall, S.C, 1990, Holocene Activity of the Rose Canyon Fault in San Diego,
Califomia, Based on Trench Exposures and Tectonic Geomorphology; Geological Society
of America, Abstracts with Programs.
, 1991, Minimum Holocene Slip Rate for the Rose Canyon Fauh in San Diego, Califomia in
EnvironmentalPerils, San Diego Region: San Diego Association of Geologists, p. 37-46.
Tan, S.S., and Kennedy, M.P., 1996, Geologic Maps of the Northwestem Part of San Diego County,
Califomia: Califomia Division of Mines and Geology, DMG Open-File Report 96-02 2
Plates.
Tan, S.S., and Giffen, D.G., 1995, Landslide Hazards in the Northem Port ofthe San Diego Metropolitan
Area, San Diego County, Califomia, Landslide Hazard Identification Map No. 3 5, Division
of Mines and Geology, Open-File Report No. 95-04.
Treiman, J.A., 1993, The Rose Canyon Fauh Zone, Southem Califomia: Califomia Division of Mines and
Geology, Open-File Report 93-02,45 p.
Seed, H.B., and Idriss, I.M., 1982, Ground Motions and Soil Liquefaction During Earthquakes, Monogram
Series, Earthquake Engineering Research Institute, Berkeley, Califomia.
Seed, H.B., Idriss, I.M., and Arango, I., 1983, Evaluation of Liquefacfion Potential Using Field Performance
Data, Joumal of Geotechnical Engineering: ASCE, Volume 109, March, pp. 458-482.
Treiman, J.A., 1984, The Rose Canyon Fault Zone: A Review and Analysis, Califomia Division of Mines
and Geology, Funded by Federal Management Agency Cooperative Agreement EMF-83-
K-0148.
, 1993, The Rose Canyon Fauh Zone, Southem Califomia: Califomia Division of Mines and
Geology, Open-File Report 93-2,45p.
Weber, F.H., 1982, Recent Slope Failures, Ancient Landslides and Related Geology ofthe Northem-Central
Coastal Area, San Diego County, Califomia: Califomia Division of Mines and Geology
Open File Report 82-12LA, 77 p.
Wilson, K.L., 1972, Eocene and Related Geology of a Portion of the San Luis Rey and Encinitas
Quadrangles, San Diego County, Califomia: Master Thesis, University of California at
Riverside, 123 p.
A-3
971009-005
APPENDIX A (continued)
Ziony, J.I., and Yerkes, R.F., 1985, Evaluating Earthquake and Surface-FauhingPotential in Ziony, ed.,
1985, Evaluating Earthquake Hazards in the Los Angeles Region - An Earth - Science
Perspective: U.S. Geological Survey, Professional Paper 1360, pp. 43-91.
Aerial Photographs
Date Source FUght Photo No(s)
4/11/53 USDA AXN-8M 19-21
A-4
971009-005
APPENDIXC
Laboratorv Testing Procedures and Test Results
Atterberg Limits: The Atterberg Limits were determined in accordance with ASTM Test Method D4318 for
engineering classification of the fine-grained materials and presented in the table below:
Sample Location Liquid
Limit (%)
Plastic
Limit (%)
Plastic
Index (%)
USCS Soil
Classification
B-2 #7 (§40' 35 16 19 CL
B-3 #7 (§30' 39 16 22 CL
B-5 #6 @20' 42 20 22 CL
B-6#4@15' 42 17 25 CL
Direct Shear Tests: Direct shear tests were performed on selected remolded and/or undisturbed samples,
which were soaked for a minimum of 24 hours under a surcharge equal to the applied normal force during
testing. After transfer of the sample to the shear box and reloading of the sample, the pore pressures set up
in the sample (due to the transfer) were allowed to dissipate for a period of approximately 1 hour prior to
application of shearing force. The samples were tested under various nonnal loads utilizing a motor-driven,
strain-controlled, direct-shear testing apparatus at a strain rate of less than 0.001 to 0.5 inches per minute
(depending upon the soil type). The test results are presented in the test data.
Sample Location Sample Description Test Type Friction Angle
(degrees)
Apparent
Cohesion (psf)
LB-25 #3 @ 11-
14' Pale brown silty SAND Remolded to
90% 30 460
LB-25 #8@53' Green gray CLAY Remolded to
90% 26 180
LB-26 #4 @ 20' Pale green sandy CLAY Undisturbed 25 750
LB-28 #1 (§ 10' Pale yellow silty SAND Undisturbed 25 100
Moisture and Density Determination Tests: Moisture content and dry density determinations were
performed on relatively undisturbed samples obtained from the test borings and/or trenches. The results of
these tests are presented in the boring and/or trench logs. Where applicable, only moisture content was
determined from "undisturbed" or disturbed samples.
C-1
971009-005
APPENDIXC (Continued)
Expansion Index Tests: The expansion potential of selected materials was evaluated by the Expansion Index
Test, U.B.C. Standard No. 18-2 and/or ASTM Test Method 4829. 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 l-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:
Sample Location Sample Description Compacted Dry
Density (pcf)
Expansion
Index
Expansion
Potential
Light brown clayey silty sand to
sandy clay
101.5 28 Low
Maximum Drv Densitv Tests: The maximum dry density and optimum moisture content of typical materials
were determined in accordance with ASTM Test Method D1557. The results ofthese tests are presented in
the table below:
Sample Location Sample Description Maximum Dry
Density (pcf)
Optimum Moisture
Content (%)
LB-25 #3 @ 11-14' Pale brown silty SAND 117.5 13.5
LB-25 #8 @ 53' Green gray CLAY 111.0 17.5
Consolidation Tests: Consolidationtests were performed on selected, relatively undisturbed ring samples in
accordance with Modified ASTM Test Method D243 5. Samples were placed in a consolidometer and loads
were applied in geometric progression. The percent consolidation for each load cycle was recorded as the
ratio of the amount of vertical compression to the original 1 -inch height. The consolidation pressure curves
are presented on the attached figures. Where applicable, time-rates of consolidation were recorded and
presented below:
Sample Location Coefficientof Consolidation C
(cmVsec)
B-2 @20' 2.2 X 10-'
B-3 @20' 2.3 X 10-"
B-5 @ 15' 2.9 X 10^
C-2
TERATEST LABS, INC.
DIRECT SHEAR TEST RESULT
ASTIVI D 3080
Project Name:
Project Number:
Boring Number:
Sample Number:
Soil Description:
BRESSI RANCH
971009-005
LB-25
3
PALE BROWN SILTY SAND (SM)
Date:
Tested By:
Checked By:
Depth (ft.):
10/31/00
BCC
11.0-14.0
VERTICAL STRESS
(psf)
PROVING RING
DIAL READING
CONVERSI SHEAR RELAXED PEAK VERTICAL STRESS
(psf)
PROVING RING
DIAL READING ON STRESS STRESS COHESION (psf) 550 VERTICAL STRESS
(psf)
PROVING RING
DIAL READING FACTOR (psf) (psf) FRICTION (deg.) 35
PEAK RELAXED
554 51 44 15 765 660 RELAXED
1108 101 83 15 1515 1245 COHESION (psf) 460
2216 127 104 15 1905 1560 FRICTION (deg.) 30
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00
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00
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00
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00 u •
( ) 5( DO 10 00 15
STRESS (psf)
00 20 00 25 00
TERA TEST LA BS. INC.
DIRECT SHEAR TEST RESULT
ASTM D 3080
Project Name:
Project Number:
Boring Number:
Sample Number:
Soil Description:
BRESSI RANCH
971009-005
LB-25
8
GREENISH GRAY LEAN CLAY (CL)
Date
Tested By
Checked By
Depth (ft.)
10/31/00
BCC
53.0
VERTICAL STRESS
(psf)
PROVING RING
DIAL READING
CONVERSI
ON
FACTOR
SHEAR
STRESS
(psf)
RELAXED
STRESS
(psf)
PEAK VERTICAL STRESS
(psf)
PROVING RING
DIAL READING
CONVERSI
ON
FACTOR
SHEAR
STRESS
(psf)
RELAXED
STRESS
(psf)
COHESION (psO 200 VERTICAL STRESS
(psf)
PROVING RING
DIAL READING
CONVERSI
ON
FACTOR
SHEAR
STRESS
(psf)
RELAXED
STRESS
(psf) FRICTION (deg.) 30
PEAK RELAXED
554 35 31 15 525 465 RELAXED
1108 54 45 15 810 675 COHESION (psf) 180
2216 99 86 15 1485 1290 FRICTION (deg.) 26
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00 STRAIN (psf) i \
00 STRAIN (psf) 00 STRAIN (psf) 00 STRAIN (psf) 00 STRAIN (psf) 00 STRAIN (psf) 00 00 00 00 00 00 00
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STRESS (psf)
00 20 00 25 00
TERATEST LABS. INC.
DIRECT SHEAR TEST RESULT
ASTM D 3080
Project Name:
Project Number:
Boring Number
Sample Number:
Soil Description:
BRESSI RANCH
971009-005
LB-26
4
PALE GREEN SANDY LEAN CLAY s(CL)
Date
Tested By
Checked By
Depth (ft.)
10/30/00
BCC
20,0
VERTICAL STRESS
(psO
PROVING RING
DIAL READING
CONVERSI
ON
FACTOR
SHEAR
STRESS
(psO
RELAXED
STRESS
(psf)
PEAK VERTICAL STRESS
(psO
PROVING RING
DIAL READING
CONVERSI
ON
FACTOR
SHEAR
STRESS
(psO
RELAXED
STRESS
(psf)
COHESION (psf) 750 VERTICAL STRESS
(psO
PROVING RING
DIAL READING
CONVERSI
ON
FACTOR
SHEAR
STRESS
(psO
RELAXED
STRESS
(psf) FRICTION (deg.) 29
PEAK RELAXED
554 77 74 15 1155 1110 RELAXED
1108 84 78 15 1260 1170 COHESION (psf) 750
2216 138 127 15 2070 1905 FRICTION (deg.) 25
2000 •
00
2000 •
\
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00
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STRESS (psf)
00 20 00 25 00
TERATEST LABS, INC.
DIRECT SHEAR TEST RESULT
ASTM D 3080
Project Name:
Project Number:
Boring Number:
Sample Number:
Soil Description:
BRESSI RANCH
971009-005
LB-28
1
Date
Tested By
Checked By
Depth (ft.)
10/30/00
BCC
r 10. 0
PALE YELLOW POORLY-GRADED SAND WITH SILT (SP-SM)
VERTICAL STRESS
(psf)
PROVING RING
DIAL READING
CONVERSI
ON
FACTOR
SHEAR
STRESS
(psf)
RELAXED
STRESS
(psf)
PEAK VERTICAL STRESS
(psf)
PROVING RING
DIAL READING
CONVERSI
ON
FACTOR
SHEAR
STRESS
(psf)
RELAXED
STRESS
(psf)
COHESION (psO 100 VERTICAL STRESS
(psf)
PROVING RING
DIAL READING
CONVERSI
ON
FACTOR
SHEAR
STRESS
(psf)
RELAXED
STRESS
(psf) FRICTION (deg.) 49
PEAK RELAXED
554 33 30 15 495 450 RELAXED
1108 103 98 15 1545 1470 COHESION (psO 100
2216 160 147 15 2400 2205 FRICTION (deg.) 47
Leighton and Associates, Inc.
GENERAL EARTHWORK AND GRADING SPECIFICATIONS
Page 1 of 6
LEIGHTON AND ASSOCIATES, INC.
GENERAL EARTHWORK AND GRADING SPECIFICATIONSFOR ROUGH GRADING
1.0 General
1.1 Intent: These General Earthwork and Grading Specifications are for the grading and
earthwork shown on the approved grading plan(s) and/or indicated in the geotechnical
report(s). These Specifications are a part of the recommendations contained in the
geotechnical report(s). In case of conflict, the specific recommendations in the
geotechnical report shall supersede these more general Specifications. Observations of the
earthwork by the project Geotechnical Consultant during the course of grading may result
in new or revised recommendations that could supersede these specifications or the
recommendations in the geotechnical report(s).
1.2 The Geotechnical Consultant of Record: Prior to commencement of work, the owner shall
employ the Geotechnical Consultant of Record (Geotechnical Consultant). The
Geotechnical Consultants shall be responsible for reviewing the approved geotechnical
report(s) and accepting the adequacy of the preliminarygeotechnical findings, conclusions,
and recommendationsprior to the commencementof the grading.
Prior to commencement of grading, the Geotechnical Consultant shall review the "work
plan" prepared by the Earthwork Contractor (Contractor) and schedule sufficient personnel
to perform the appropriate level of observation, mapping, and compaction testing.
During the grading and earthwork operations, the Geotechnical Consultant shall observe,
map, and document the subsurface exposures to verify the geotechnical design
assumptions. If the observed conditions are found to be significantly different than the
interpreted assumptions during the design phase, the Geotechnical Consultant shall inform
the owner, recommend appropriate changes in design to accommodate the observed
conditions, and notify the review agency where required. Subsurface areas to be
geotechnically observed, mapped, elevations recorded, and/or tested include natural ground
after it has been cleared for receiving fill but before fill is placed, bottoms of all "remedial
removal" areas, all key bottoms, and benches made on sloping ground to receive fill.
The Geotechnical Consultant shall observe the moisture-conditioningand processing of the
subgrade and fill materials and perform relative compaction testing of fill to determine the
attained level of compaction. The Geotechnical Consultant shall provide the test results to
the owner and the Contractor on a routine and frequent basis.
3030.1094
Leightonand Associates,Inc.
GENERAL EARTHWORK AND GRADING SPECIFICATIONS
Page 2 of 6
••3 The Earthwork Confractor: The Earthwork Contractor (Contractor) shall be qualified,
experienced, and knowledgeable in earthwork logistics, preparation and processing of
ground to receive fill, moisture-conditioningand processing of fill, and compacting fill.
The Contractor shall review and accept the plans, geotechnical report(s), and these
Specifications prior to commencement of grading. The Contractor shall be solely
responsible for performing the grading in accordance with the plans and specifications.
The Contractor shall prepare and submit to the owner and the Geotechnical Consultant a
work plan that indicates the sequence of earthwork grading, the number of "spreads" of
work and the estimated quantities of daily earthwork contemplated for the site prior to
commencement of grading. The Contractor shall inform the owner and the Geotechnical
Consultant of changes in work schedules and updates to the work plan at least 24 hours in
advance of such changes so that appropriate observations and tests can be planned and
accomplished. The Contractor shall not assume that the Geotechnical Consultant is aware
of all grading operations.
The Contractor shall have the sole responsibility to provide adequate equipment and
methods to accomplish the earthwork in accordance with the applicable grading codes and
agency ordinances, these Specifications, and the recommendations in the approved
geotechnical report(s) and grading plan(s). If, in the opinion of the Geotechnical
Consultant, unsatisfactory conditions, such as unsuitable soil, improper moisture condition,
inadequate compaction, insufficient buttress key size, adverse weather, etc., are resulting in
a quality of work less than required in these specifications, the Geotechnical Consultant
shall reject the work and may recommend to the owner that construction be stopped until
the conditions are rectified.
2.0 Preparation of Areas to be Filled
2.1 Clearing and Grabbing: Vegetation, such as brash, grass, roots, and other deleterious
material shall be sufficiently removed and properly disposed of in a method acceptable to
the owner, goveming agencies, and the GeotechnicalConsultant.
The Geotechnical Consultant shall evaluate the extent of these removals depending on
specific site conditions. Earth fill material shall not contain more than 1 percent of organic
materials (by volume). No fill lift shall contain more than 5 percent of organic matter.
Nesting of the organic materials shall not be allowed.
If potentially hazardous materials are encountered, the Contractor shall stop work in the
affected area, and a hazardous material specialist shall be informed immediately for proper
evaluation and handlingof these materials prior to continuingto work in that area.
As presently defined by the State of Califomia, most refined petroleum products (gasoline,
diesel fuel, motor oil, grease, coolant, etc.) have chemical constituents that are considered
to be hazardous waste. As such, the indiscriminate dumping or spillage of these fluids
onto the ground may constitute a misdemeanor, punishable by fines and/or imprisonment,
and shall not be allowed.
3030.1094
Leighton and Associates, Inc.
GENERAL EARTHWORK AND GRADING SPECIFICATIONS
Page 3 of 6
2.2 Processing: Existing ground that has been declared satisfactory for support of fill by the
Geotechnical Consultant shall be scarified to a minimum depth of 6 inches. Existing
ground that is not satisfactory shall be overexcavated as specified in the following section.
Scarification shall continue until soils are broken down and free of large clay lumps or
clods and the working surface is reasonably uniform, flat, and free of uneven features that
would inhibit uniform compaction.
2.3 Overexcavation: In addition to removals and overexcavations recommended in the
approved geotechnical report(s) and the grading plan, soft, loose, dry, saturated, spongy,
organic-rich, highly fractured or otherwise unsuitable ground shall be overexcavated to
competent ground as evaluated by the Geotechnical Consultant during grading.
2.4 Benching: Where fills are to be placed on ground with slopes steeper than 5:1 (horizontal
to vertical units), the ground shall be stepped or benched. Please see the Standard Details
for a graphic illustration. The lowest bench or key shall be a minimum of 15 feet wide and
at least 2 feet deep, into competent material as evaluated by the Geotechnical Consultant.
Other benches shall be excavated a minimum height of 4 feet into competent material or as
otherwise recommended by the Geotechnical Consultant. Fill placed on ground sloping
flatterthan 5:1 shall also be benched or otherwise overexcavated to provide a flat subgrade
forthefiU.
2.5 Evaluation/Acceptance of Fill Areas: All areas to receive fill, including removal and
processed areas, key bottoms, and benches, shall be observed, mapped, elevations
recorded, and/or tested prior to being accepted by the Geotechnical Consultant as suitable
to receive fill. The Contractor shall obtain a written acceptance from the Geotechnical
Consultant prior to fill placement. A licensed surveyor shall provide the survey control for
determiningelevationsof processed areas, keys, and benches.
3.0 Fill Material
3.1 General: Material to be used as fill shall be essentially free of organic matter and other
deleterious substances evaluated and accepted by the Geotechnical Consultant prior to
placement. Soils of poor quality, such as those with unacceptable gradation, high
expansion potential, or low strength shall be placed in areas acceptable to the Geotechnical
Consultantor mixed with other soils to achieve satisfactoryfill material.
3.2 Oversize: Oversize material defined as rock, or other irreducible material with a maximum
dimension greater than 8 inches, shall not be buried or placed in fill unless location,
materials, and placement methods are specifically accepted by the Geotechnical
Consultant. Placement operations shall be such that nesting of oversized material does not
occur and such that oversize material is completely surrounded by compacted or densified
fill. Oversize material shall not be placed within 10 vertical feet of finish grade or within
2 feet offuture utilities or underground constraction.
3030.1094
Leightonand Associates,Inc.
GENERAL EARTHWORK AND GRADING SPECIFICATIONS
Page 4 of 6
3.3 Import: If importing of fill material is required for grading, proposed import material shall
meet the requirements of Section 3.1. The potential import source shall be given to the
Geotechnical Consultant at least 48 hours (2 working days) before importing begins so that
its suitability can be determined and appropriate tests performed.
4.0 Fill Placementand Compaction
4.1 Fill Layers: Approved fill material shall be placed in areas prepared to receive fill (per
Section 3.0) in near-horizontal layers not exceeding 8 inches in loose thickness. The
Geotechnical Consultant may accept thicker layers if testing indicates the grading
procedures can adequately compact the thicker layers. Each layer shall be spread evenly
and mixed thoroughlyto attain relative uniformity of materialand moisture throughout
4.2 Fill Moisture Conditioning: Fill soils shall be watered, dried back, blended, and/or mixed,
as necessary to attain a relatively uniform moisture content at or slightly over optimum.
Maximum density and optimum soil moisture content tests shall be performed in
accordance with the American Society of Testing and Materials (ASTM Test Method
D1557-91).
4.3 Compaction of Fill: After each layer has been moisture-conditioned, mixed, and evenly
spread, it shall be uniformly compactedto not less than 90 percentof maximum dry density
(ASTM Test Method D1557-91). Compaction equipment shall be adequately sized and be
either specifically designed for soil compaction or of proven reliability to efficiently
achieve the specified level of compaction with uniformity.
4.4 Compaction of Fill Slopes: In addition to normal compaction procedures specified above,
compaction of slopes shall be accomplished by backrolling of slopes witb sheepsfoot
rollers at increments of 3 to 4 feet in fill elevation, or by other methods producing
satisfactory results acceptable to the Geotechnical Consultant. Upon completion of
grading, relative compaction of the fill, out to the slope face, shall be at least 90 percent of
maximum density per ASTM Test Method Dl 557-91.
4.5 Compaction Testing: Field tests for moisture content and relative compaction of the fill
soils shall be performed by the Geotechnical Consultant. Location and frequency of tests
shall be at the Consultant's discretion based on field conditions encountered. Compaction
test locations will not necessarily be selected on a random basis. Test locations shall be
selected to verify adequacy of compaction levels in areas that are judged to be prone to
inadequate compaction (such as close to slope faces and atthe fill/bedrock benches).
3030.1094
Leightonand Associates,Inc,
GENERAL EARTHWORK AND GRADING SPECIFICATIONS
Page 5 of 6
4.6 Frequencv of Compaction Testing: Tests shall be taken at intervals not exceeding 2 feet in
vertical rise and/or 1,000 cubic yards of compacted fill soils embankment In addition, as a
guideline, at least one test shall be taken on slope faces for each 5,000 square feet of slope
face and/or each 10 feet of vertical height of slope. The Contractor shall assure that fill
construction is such that the testing schedule can be accomplished by the Geotechnical
Consultant, The Contractor shall stop or slow down the earthwork construction if these
minimum standards are not met.
4-7 Compaction Test Locations: The Geotechnical Consultant shall document the approximate
elevation and horizontal coordinates of each test location. The Contractor shall coordinate
with the project surveyor to assure that sufficient grade stakes are established so that the
Geotechnical Consultant can determine the test locations with sufficient accuracy. At a
minimum, two grade stakes within a horizontal distance of 100 feet and vertically less than
5 feet apart from potential test locations shall be provided.
5.0 Subdrain Installation
Subdrain systems shall be installed in accordance with the approved geotechnical report(s), the
grading plan, and the Standard Details. The Geotechnical Consultant may recommend additional
subdrains and/or changes in subdrain extent, location, grade, or material depending on conditions
encountered during grading. All subdrains shall be surveyed by a land surveyor/civil engineer for
line and grade after installation and prior to burial. Sufficient time should be allowed by the
Contractor for these surveys.
6.0 Excavation
Excavations, as well as over-excavation for remedial purposes, shall be evaluated by the
Geotechnical Consultant during grading. Remedial removal depths shown on geotechnical plans
are estimates only. The actual extent of removal shall be determined by the Geotechnical
Consultant based on the field evaluation of exposed conditions during grading. Where fill-over-cut
slopes are to be graded, the cut portion of the slope shall be made, evaluated, and accepted by the
Geotechnical Consultant prior to placement of materials for construction ofthe fill portion of the
slope, unless otherwise recommended by the Geotechnical Consultant
Leighton and Associates, Inc.
GENERAL EARTHWORK AND GRADING SPECIRCATIONS
Page 6 of 6
7.0 Trench Backfills
7.1 The Contractor shall follow all OHSA and Cal/OSHA requirements for safety of trench
excavations.
7.2 All bedding and backflll of utility trenches shall be done in accordance with the applicable
provisions of Standard Specifications of Public Works Construction. Bedding material
shall have a Sand Equivalent greaterthan 30 (SE>30). The bedding shall be placed to 1
foot over the top of the conduit and densified by jetting. Backfill shall be placed and
densified to a minimum of 90 percent of maximum from 1 foot above the top of the
conduit to the surface.
7.3 The jetting of the bedding around the conduits shall be observed by the Geotechnical
Consultant.
7.4 The GeotechnicalConsultantshall test the trench backflll for relative compaction. At least
one test should be made for every 300 feet of trench and 2 feet of fill.
7.5 Lift thickness of trench backflll shall not exceed those allowed in the Standard
Specifications of Public Works Construction unless the Contractor can demonstrate to the
Geotechnical Consultant that the fill lift can be compacted to the minimum relative
compaction by his altemative equipment and method.
PROJECTEO PtANE
1 TOI MAXIMUM FROM TOE
OF SLOPE TO APPROVED OROUNO
NATURAL
OROUND
FILL SLOPE
r MIN.
KEY DEPTH
L—18' MIN.
LOWEST BENCH
(KEY)
REMOVE
UNSUITABLE
MATERIAL
BENCH
HEIOHT
NATURAL
OROUND
• ^S• MIN.—H
LOWEST BENCHt
2' MiN.
KEY DEPTH
IMPACTED—
4'TyPK:AL
BENCH
HEK3HT
REMOVE
UNSUrrABLE
MATERIAL
FILL-OVER-CUT
SLOPE
OUTFACE
8HAa BE CON8TRUCTB) PRK)R
TO FMJL PlACEMBfT TO ASSURE
ADEQUATE QEOLOQC CONDfTlONS
OUTFACE
TO BE CONSTRUCTED PRIOR
TO Fia PLACEMENTv
NATURAL
QROUNO
OVERBUILT AND
TRIM BACK
PROJECTED PLANE
1 TOI MAXIMUM FROM
TOE OF SLOPE TO
APPROVED GROUND''
DESION SLOPE REMOVE
NSUITABLE
MATERIAL
CUT-OVER-FILL
SLOPE
For Subdrains See
Standard Detail C
initri 4'TYPICAL
2' MIN.
KEY DEPTH
_J L_i«'Mirt_J
— |LOWE8TBENCH|
^ (KEY)
BENCH BENCH HEIOHT
Ba^CHINO SHAU BE DONE WHEN SLOPES
ANQLE IS EQUAL TO OR GREATER THAN 5:1
MINMUM BB4CH HEIQHT SHALL BE 4 FEET
MINIMUM Fia WIDTH SHALL BE 9 FEET
KEYING AND BENCHING GENERAL EARTHWORK AND GRADING
SPECIFICATIGNS
STANDARD DETAILS A
REV. 4/11/96
FINISH GRADE
SLOPE
FACE
-10' MIN.—"COMPACTED FILL-:"-—
rOVERSIZE
;=^5?5irir:r::_-IWINDROW
• Oversize rock Is larger than 8 Inches
in largest dinienskxi.
• Excavate a trench in the compacted
fill deep enough to bury all the rock.
• Backfill with granular soil jetted or
fkxxjed in place to fill all the vokis.
• Do not buiy rock within 10 feet of
finish grade.
• Windrow of buried rock ShaH be
parallel to the finished sk)pe fiH.
JETTED OR FLOODED
GRANULAR MATERiAL
ELEVATION A-A'
PROFILE ALONG WINDROW
A-
JETTED OR FLOODED
GRANULAR MATERIAL
OVERSIZE
ROCK DISPOSAL
GENERAL EARTHWORK AND GRADINQ
SPECIFICATIONS
STANDARD DETAILS B
4/95
NATURAL
GROUND
BENCHING REMOVE
UNSUITABLE
MATERIAL
OVERLAP FROM THE TOP
IED EVERY 6 FEET
CALTRANS CLASS II
PERMEABLE OR #2 ROCK"
(9FT.'/FT.) WRAPPED IN
FILTER FABRIC
FILTER FABRIC
(MIRAFI 14C
APPROVED
EQUIVALENT)
CANYON SUBDRAIN OUTLET DETAIL
DESIGN
FINISHED
GRADE
PERFORATED PIPE
6-<|> MIN.
V COLLECTOR PIPE SHALL
BE MINIMUM 6- DIAMETER
SCHEDULE 40 PVC PERFORATED
PIPE. SEE STANDARD DETAiL D
FOR PIPE SPECIFICATION
.NON-PERFORATED
6-<^ MIN.
FILTER FABRIC
(MIRAFI 140 OR
APPROVED
EQUIVALENT)
#2 ROCK WRAPPED IN FILTER
FABRIC OR CALTRANS CLASS II
PERMEABLE.
CANYON SUBDRAINS GENERAL EARTHWORK AND GRADING
SPECIFICATIONS
STANDARD DETAILS C
4/95
OUTLET PIPES
NON-PERFORATED PIPE,
100' MAX. O.C. HORIZONTALLY,
30' MAX. O.C. VERTICALLY
POSITIVE SEAL
SHOULD BE
PROVIDED AT
THE JOI
|5?6
OUTLET PIPE
(NON-PERFORATED)
CALTRANS CLASS II
PERMEABLE OR #2 ROCK
(3FT.»/FT.) WRAPPED IN
FILTER FABRIC
12" MIN. OVERLAP FROM THE TOP
HOG RING TIED EVERY 6 FEET
\
FILTER FABRIC
(MIRAFI 140 OR
APPROVED
EQUIVALENT)
/
T-CONNECTION FOR
COLLECTOR PIPE TO
OUTLET PIPE
• SUBDRAIN INSTALLATION - Subdrain collector pipe shall be Installed with perfofattons down or.
unless othen/vise designated by the geotechnical consultant Outlet pipes shall be non-perforated
pipe. The subdrain pipe shall have at least 8 pefforatkxis unifonnly spaced per foot Perforation shall
be Vi" to Vi* If drilled holes are used. All subdrain pipes shall have a gradient at least 2% towards the
outlet
• SUBDRAIN PIPE - Subdrain pipe shall be ASTM D27S1, SDR 23.5 or ASTM D1527, Schedule 40, or
ASTM D3034, SDR 23.5, Schedule 40 Polyvinyl Chtoride Piastte (PVC) pipe.
• All outlet pipe shall be placed in a trench no wWer than twtee the subdrain pipe. Pipe shall be in soii
of SE>30 jetted or fiooded in place except for the outside 5 feet whteh shali be native soil backfill.
BUTTRESS OR
REPLACEMENT FILL
SUBDRAINS
GENERAL EARTHWORK AND GRADING
SPECIFICATIONS
STANDARD DETAILS D
4/95