HomeMy WebLinkAboutCT 02-22; LA COSTA GREENS NEIGHBORHOOD 1.10; GEOTECHNICAL REPORT; 2004-06-23I_ I ;
UPDATE
GEOTECHNICAL REPORT
VILLAGES OF LA COSTA
THE GREENS
NEIGHBORHOOD 1.09
LOTS 1 THROUGH 75
CARLSBAD,' CALIFORNIA
PREPARED FOR
D. R. HORTON'
WESTERN PACIFIC HOUSING SERIES
CARLSBAD, CALIFORNIA
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JUNE 23, 2004
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GEOCON:
INCORPORATED
GEOTECHNICAL CONSULTANTS (4 4&>)
Project No. 06403-52-13
June 23, 2004
D. R. Horton, Western Pacific Housing Series
5790 Fleet Street, Suite 210
Carlsbad, California 92009
Attentions Mr. Kurt Bausback
Subject: VILLAGES OF LA COSTA THE GREENS.
NEIGHBORHOOD 1.09, LOTS 1 THROUGH 75
CARLSBAD, CALIFORNIA
UPDATE GEOTECHNICAL REPORT
Gentlemen:
In accordance with your authorization of our Proposal No. LG-03536 dated October 21, 2003, we
have prepared this update geotechnical report for the subject project. The accompanying report
presents the results of our study and contains conclusions and recommendations pertaining to the
geotechnical aspects of the proposed development of the site. Provided that the recommendations
contained in this update report are followed, the site is considered suitable for construction and
support of the proposed structures and improvements as presently planned.
Should you have any questions regarding this report, or if we may be of further service, please
contact the undersigned at your convenience.
Very truly yours,
GEOCON INCORPORATED
Michael C. ae. dL 44heodacker
Staff Geologist G 1778 RCE 63291
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MCE:AS: SR:dmc
(4/del) Addressee
(9/del) Permit Us
Attention: Ms. Stacy Sapp
6960 Flanders Drive 0 San Diego, California 92121-2974 0 Telephone (858) 558-6900 0 Fax (858) 558.6159
TABLE OF CONTENTS
1. PURPOSE AND.SCOPE .. 1
2. PREVIOUS. SITE DEVELOPMENT ..............................................................................................1
3. SITE AND PROJECT DESCRIPTION............................................................................................1
4. SOIL AND GEOLOGIC CONDITIONS ......................................................................................... 2
4.1 Compacted Fill (Qcf) .............................................................................................................2
4.2 Santiago Formation (Ts) ....................................................................................................... 3
5. GROUNDWATER ............................................................................................................................ 3
6. GEOLOGIC HAZARDS ..................................................................................... .............................. 3
6.1 Faulting and. Seismicity ...........................................................................................................3
6.2 Liquefaction ...................................... ....................................................................................... 4
6.3 Landslides ........ . .......... ................................ .. ....... .................. ........ ............................................... 4
7. . CONCLUSIONS AND RECOMMENDATIONS ....
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....................................................................... 5
7.1 General— ............. .................................... . ...................... ........ ....... ............................................... 5
7.2 Seismic Design .......... . .......... .................................................... ........t. . .....................................5
7.3 Finish Grade Soil Conditions.. ................................................................................................. 6
7.4 Future Grading ................................................................ ......................................................... 7
7.5 Foundations ....................................................................................... ......................................7
7.6 Retaining Walls ....................... ..............................................................................................11
7.7 Lateral Load ........................................................................................................................12
7.8 Slope Maintenance, ... . ...... . ....................................................................................... . ........... 12
7.9 Site Drainage .................... ................................................ ....................................... ............. 13
LIMITATIONS AND UNIFORMITY OF CONDITIONS
Figures: . .
'Vicinity Map . . . .
Typical Retaining Wall Drain Detail . .
Tables: . . .
Summary of As-Graded Building Pad Conditions and Foundation Categoiy
Summary of Laboratory Water-Soluble Sulfate Test Results
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I UPDATE GEOTECHNICAL REPORT
- 1. PURPOSE AND SCOPE
- This report presents the results of the update geotechnical study for the proposed residential
development of Neighborhood 1.09, Lots 1 through 75 and associated improvements located in the I Villages of La Costa - The Greens development. The site is situated south of future Poinsettia Lane,
west of the existing La Costa Resort and Spa golf course in Carlsbad, California (see Vicinity Map,
I Figure 1). The purpose of this update report is to provide foundation and retaining wall design
recommendations.
The scope of the study included a review ofthe following:
I. 1. Update Soil, and Geological Investigation, Volume j and II, Village's of La Costa - The
Greens, Carlsbad, California, prepared by Géocbti thcororted, dated June 25, 2001
(Project No. 06403-12-03).
Final Report of Testing and Observation Services Performed During Site Grading, Villages
of La Costa.— The Greens, Neighborhood 1. 09, Carlsbad, California, prepared by Geocon
I Incorporated, dated June 21, 2004. (Project No.06403-52709).
Grading Plans and Erosion Control plans for: La Costa. Greens Neighborhood 1.09,
I . prepared by Hunsaker and Associates, City-of Carlsbad approval dated May 6, 2004.
2. PREVIOUS SITE DEVELOPMENT
I Neighborhood 1.09, Lots 1 through 75, was graded to finish-pad configuration during mass grading
operations for the Villages of La Costa - The Greens development. Grading was performed in
I conjunction with the observation and testing services, of Geocon Incorporated. A summary of the
- observations, compaction test results, and professional opinions pertaining to the grading are
I presented in the above-referenced final report of grading. Mass grading for the subject site has been
completed and consisted of developing 75 single-family residential lots and associated streets. Fill
slopes were constructed with design inclinations of 2:1 (horizontal:vertical) or flatter, with a
maximum height of approximately 40 feet. Maximum thickness of the fill soils is approximately 65
feet. An "As-Graded" Geologic Map is provided in the above-referenced final report and depicts the
existing geologic conditions and topography.
I 3. SITE AND PROJECT DESCRIPTION
The development of The Greens - Neighborhood 1.09 consists of 75 single-family residential homes,
I .and associated improvements. Compacted fill soils and the Santiago Formation are exposed at grade
throughout the site. A summary of the as-graded pad conditions for the lots is provided on Table I. In
general, the on-site fill materials generally vary between angular gravels and boulders produced by
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I onsite blasting of hard metavolcanic rock to clayey, fine sands, sandy to silty clay, and sandy to
clayey gravelsderived from excavations within surficial soils and the Santiago Formation.
I The locations and descriptions of the site and proposed improvements are based on a site recon-
naissance, a review of the referenced grading plans, and our understanding of project development, if
I project details vary significantly from those described above, Geocon Incorporated should be
contacted to determine the necessity for review and revision of this report.
4. SOIL AND GEOLOGIC CONDITIONS
The Santiago Formation and compacted fill soils underlie the site. The predoinant materials within
4 feet of grade generally consist of clayey to silty sand and sandy clay and possess a low to high
expansion potential. The soil types and geologic unit are discussed below.
4.1 Compacted Fill (Qcf)
In general, structural fill placed and compacted at the site consisted of mateiial which can be
classified into three zones:
Zone A - Material placed within 3 feet from pad grade, 6 feet from parkway grade, and
within roadways to at least 1 foot below the deepest utility consisted of "soil" fill with a
maximum particle dimension of 6 inches.
Zone B - Material placed within 10 feet from pad grade and below Zone A consisted of
"soil rock" fill with a maximum particle dimension of 12 inches. In addition, material
placed on the outer 6 feet of fill slopes and 2 feet below Zone A for fills in roadways and
parkways consisted of "soil rock" fill with a maximum particle dimension of 12 inches.
Zone C - Material placed below Zone B consisted of "soil rock" fill and "rock" fill with a
maximum particle dimension of 48 inches. It should also be noted that larger rocks with a
maximum dimension of approximately 8 feet Were buried individually during "soil-rock"
fill grading operations.
The maximum fill thickness is approximately 65 feet and was placed in conjunction with the
observation and testing services of Geocon Incorporated and reported in the above-referenced final
report of grading. The compacted fill soils are considered suitable to provide adequate support for the
proposed development.
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Santiago Formation (Is)
The Eocene-aged Santiago Formation, consisting of dense, massive, white to light green, silty, fine to
coarse sandstones and hard, greenish-gray to brown, claystones and, siltstones are exposed at finish
grade on cut lots and underlie the compacted fill at the site and are considered suitable for the support
of the proposed development.
5.. GROUNDWATER
Groundwater was encountered during grading operations and is not anticipated to adversely impact
the development of the property due to the installation of canyon subdrains and stability fills. Due to
the variable nature of the Santiago Formation, which consists of. interbedded sandstone and
claystone/siltstone, seepage was mitigated during rmedial grading by. installation of canyon
subdrains and construction of stability fills. It is not uncommon for, groundwater or seepage
conditions to develop where none previously existed. Groundwater elevations, are dependent on
seasonal precipitation, irrigation and land use, among other factors, and vary as a result. Proper
surface drainage of irrigation and rainwater will be important to futur,e performance of the project.
6. GEOLOGIC HAZARDS
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6.1 Faulting and Seismicity
Our review of pertinent geologic literature, the previously referenced geoteclmical investigation
report dated June 25, 2001, and our experience with the soil and geologic conditions in the general
1 ' area indicate that no known active or potentially active are located at the site. During grading inter-
formational inactive faults were exposed and are shown on the "As-Graded" Geologic Map.
The nearest known "active" faults are the Rose Canyon Fault and the Newport-Inglewood (offshore)
located approximately 7 and 10 miles, respectively, to the west and the Coronado Banks Fault Zone, I which lies approximately 22 miles to the southeast. Portions of the Rose Canyon Fault have been
included in: a Special Study Earthquake, Fault Zone. A Maximum Credible seismic event of
I Magnitude 7.2 is postulated for the Rose Canyon Fault with an estimated Maximum Credible peak
site acceleration Of 0.32 g based on the Sadigh, et al. (1997) acceleration-attenuation relationship.
I The seismicity of the site. is influenced by both local and regional fault systems within the southern
California and northern Baja California region. Table 6.1 lists* the. fault zones that present the greatest
I seismic impact to the site.
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TABLE 61
FAULT SYSTEMS WITHIN THE SOUTHERN CALIFORNIA AND
NORTHERN BAJA CALIFORNIA REGION
Fault Name Distance from Site
. - (miles)
' Maximum
Credible Earthquake
Maximum Credible
Site Acceleration (g)
Rose Canyon . . 7 . 7.2 0.32
Newport—Inglewood (Offshore) 10 7.1 . 0.25
Coronado Bãnk Fault Zone. 22 7.6 0,17
Elsmore—Juliàn 23 7.1 0.13
Elsinore—Temecula 23 . 6.8 .. 0.10
Palos Verdes 41 7.3 0.08
Elsinore--Glen Ivy 37 6.8 . 0.06
San Jacinto—Anza 49. 7.2 0.06
In the event of a major earthquake along any of the above-referenced faults or other faults in the
Southern California region, the site could be subjected to moderate to sevre ground shaking. With
respect to seismic shaking, the site is considered comparable to others in the general vicinity. While
listing peak accelerations is useful for comparison of potential effects of fault activity in the region,
other considerations are important in seismic design including the frequency and duration of motion
and the soil conditions underlying the site. We recommend that seismic design of structures be
performed in accordance with the Uniform Building Code (UBC) currentlyadopted by the City of
Carlsbad.
6.2 Liquefaction
Liquefaction typically occurs when a site is located in a zone with seismic activity, onsite soils are
cohesionless, 'groundwater is encountered within 50 feet of the surface, and soil relative densities are
less than about 70. percent. If all four previous criteria are met, a seismic- event could result in a rapid
pore water pressure increase from the earthquake-generated ground accelerations. Due to the dense
nature of formational materials and compacted fill and the lack of permanent groundwater table, the
potential for liquefaction occurring at the site is considered to be very low.
6.3 Landslides
Examination of aerial photographs in our files, review of available geotechnical reports for the site
vicinity, our field investigation and observations during site grading indicate that no landslides are
present at the property or at a location that could impact-the site.
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T. CONCLUSIONS AND RECOMMENDATIONS.
7.1 General
7.1.1 No soil or geologic conditions were, encountered during previous geotechnical investiga-
tions or grading operations that in our opinion would preclude the continued development
of the property as presently planned, provided that the recommendations of this report are
followed.
7.1.2 The site is considered suitable for the use of conventional foundations and slab-on-grade,
and/or a post-tensioned foundation system. We understand that a post-tensioned foundation
system will be used throughout the project. Therefore, conventional footing
recommendations are not included in this report, but can be provided upon request. Design
criteria for post-tensioned slabs are provided in Section 7.5.
7.2 Seismic Design
7.2.1 The site is located within Seismic Zone 4 according to UBC Figure 16-J. Compacted fill
soils underline the proposed buildings. For seismic design, the site is characterized as soil
types Sc and SD. Table 7.2.1 summarizes site design criteria. The values listed on
Table 7.2.1 are for the Rose Canyon Fault, which is identified as a Type'B fault. The Rose
Canyon Fault is located approximately 7 miles west of the site. Table 7.2.2 presents a
summary of soil profile type for each building and the corresponding values from
Table 7.2.1 should be used for seismic design..
TABLE 7.2.1
SITE SEISMIC DESIGN CRITERIA
Parameter Soil Proffle Type
UBC Reference
Sc
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SD
Seismic Zone Factor 0.40 . 0.40 . Table 16-I
Soil Profile Sc SD Table 16-J
Seismic Coefficient, Ca 0.40 0.44 Table 16-Q
Seismic Coefficient, C,, 0.56 0.64 . Table 16-R
Near-Source Factor, Na 1.0 1.0 Table 16-S
Near-Source Factor, N,, 1.0 1.0 Table 16-T
Seismic Source B B Table 16-U
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7.2.2 Based on review of the as-graded conditions presented in the as-graded report referenced
below, as well as the seismic setting, the lots.are assigned-the seisTmic design parameters as
indicated belowin Table 7.2.2.
TABLE 7.2.2
SUMMARY OFSOIL PROFILE TYPE
Lot Nos. UBC Classification
1 SD
2 Sc
3 through 7 S0,
8 through ll Sc
12through15 Sr.
16 through 35 Sc
36 and 37
38 through 44 Sc
45 through 48 SD
49 through 52 Sc
53 SD
54th1ough60 Sc
61 and 62 SD
63 through 75 Sc
7.3 Finish Grade Soil Conditions
7.3.1 Observations and laboratory test results indicate that the prevailing soil conditions within
the upper approximately 4 feet of finish grade have an expanion potential of "low" to
"high" (Expansion Index of 130 or less) as defined by Uniform Building Code (UBC)
Table 18 -I-B. Expansion Index test results for each lot are included on Table I.
7.3.2 It should be noted that although rocks larger than 6-inch diameter were not intentionally
placed within the upper 4 feet of pad grades, some larger rocks may exist at random
locations.
7.3.3 Random samples obtained throughout the subject neighborhood were subjected to
water-soluble sulfate testing to 'evaluate the amount of water-solüble sulfates within the
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finish-grade soils. These test results are used to determine the potential for sulfate attack on
normal Portland Cement concrete. The test results indicate sulfate contents that correspond
to "negligible" to "severe" sulfate exposure ratings as defined by UBC Table 19-A4. The
results of the soluble-sulfate tests are summarized on Table H. Table 7.3 presents a•
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summary of concrete requirements set forth by UBC Table 19-A-4. It is reàommended that
the concrete used in Neighborhoods 1.09 meet the requirements for "severe" sulfate
exposure, rating, as provided on Table 7.3.
TABLE 7.3
REQUIREMENTS FOR CONCRETE EXPOSED TO
SULFATE-CONTAINING SOLUTIONS
Sulfate Water-Soluble Cement
Maximum Water Minimum
' Exposure Sulfate Percent ' to Cement Ratio Compressive
by Weight by Weight Strength (psi)
Negligible ' 0.00-0.10 --
Moderate 0.10-0.20 , II 0.50 4000
Severe 0.20-2.00 ' V " ' 0.45 4500
Very 'Svere > 2.00 - V 0.45 4500,
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7.3.4 Geocon Incorporated does not practice in the field of corrosion engineering. Therefore, if
improvements that could be susceptible to corrosion are planned, it is recommended that
further evaluation by a corrosion engineer be performed.
7.4 Future Grading
7.4.1
, Any additional grading performed at the site should be accomplished in conjunction with
our observation and compaction' testing services. Grading plans for any future grading
should be reviewed by Geocon Incorporated prior to finalizing. All trench and wall backfill
should be compacted to a dry density of at least 90 percent of the laboratory maximum dry
density at or slightly above optimum moisture content. This office should be notified at
least 48 hours prior to commencing additional grading or backfill operations.
7.5 Foundations
7.5.1 The foundation recommendations that follow are for one- or two-story residential
structures and are separated into categories dependent on the thickness and geometry of the
underlying fill soils as well as the Expansion Index (El) of the prevailing subgrade soils of
- a particular building pad. The category criteria are summarized herein.
Category I: Maximum fill thickness is less than 20 feet and Expansion Index is less than or
equal to 50.
Category II: Maximum fill thickness is less than 50 feet and Expansion Index is less than or
equal to 90, or variation in fill thickness is between 10 feet and 20 feet.
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Category III: Fill thickness exceeds 50 feet, or variation in fill thickness exceeds 20 feet, or
Expansion Index exceeds 90 but is less than 130.
Notes:
All footings should have a minimum width of 12 inches.
Footing depth is measured from lowest adjacent subgrade (including topsoil, if planned).
These depths apply to both exterior and interior footings.
All building concrete slabs should be at least 5 inches thick. This applies to both building and
garage slabs-on-grade.
All building concrete slabs should be underlain by at least 4 inches of clean sand.
All slabs expected to receive moisture sensitive floor coverings or used to store moisture-
sensitive materials should be underlain by a vapor barrier placed at the midpoint of the clean
sand recommended in No. 4 above.
7.5.2 The post-tensioned systems should be designed by a structural engineer experienced in
post-tensioned slab design and design criteria, of the Post-Tensioning Institute (UBC
Section 1816). Although this procedure was developed for expansive soils, it can also be
- used to reduce the potential for foundation distress due to differential fill settlement. The
post-tensioned design should incorporate the geotechnical parameters presented on Table
7.5 for the particular foundation category designated for each lot as presented on Table I.
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TABLE 7.5
POST-TENSIONED FOUNDATION SYSTEM DESIGN PARAMETERS
Post-Tensioning Institute (PT!)
Design Parameters
Foundation _Category
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Thornthwaite Index -20 -20 -20.
Clay Type Montmorillonite Yes Yes Yes
Clay Portion (Maximum) 30% 50% 70%
Depth to Constant Soil Suction 7.0 ft. 7.0 ft. 7.0 ft.
Soil Suction - - 3.6 ft 3.6 ft. 3.6 ft.
Moisture Velocity 0.7 in/mo. 0.7 in./mo. 0.7 in./mo.
Edge Lift Moisture Variation Distance 2.6 ft. 2.6 ft. 2.6 ft.
Edge Lift 0.41 in.. 0.78 in. 1.15 in
Center- Lift Moisture Variation Distance 5.3 ft. . 5.3 ft. 5.3 ft.
Center Lift . 2.42 in. 3.21in. 4.74in.
7.5.3 UBC Section 1816 uses interior stiffener beams in its structural design procedures. If the
structural engineer proposes a post-tensioned foundation design method other than UBC
Section 1816, it is recommended that interior stiffener beams be used for Foundation
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I Categories 11 and Ill. In addition, the depth of the perimeter foundation should be at
least 12 inches for Foundation Category I. Where the Expansion Index for a particular
building pad exceeds 50 but is less than 91, the perimeter footing depth should be at least
18 inches; and where the Expansion Index is greater than 90 and less than. 130, the
perimeter footing depth should be at least 24 inches. Geocon Incorporated should be
consulted to provide additional design parameters as required by the Structural engineer.
7.5.4 Our experience ,indicates post-tensioned-slabs may be susceptible to excessive edge lift,
regardless of the underlying soil conditions, unless, reinforcing steel is placed at the bottom
of the perimeterS footings and the interior stiffener beams. Current PTI design procedures
primarily address the potential center lift of slabs but, because of the placement of the
reinforcing tendons in' the top of the slab, the resulting eccentricity after tensioning may
reduce. the ability of the system' to mitigate edge lift. The 'foundation system should be
designed to reduce the potential for edge lift.
7.5.5 Foundations for Category I, II or ifi may be designed for an allowable soil'bearing pressure
I of 2,000 pounds per square foot (psf) (dead plus live load). This bearing pressure may be
increased by one-third for transient loads such as wind or seismic forces.
.7.5.6 , The' use of isolated footings that are located beyond the perimeter of the building
and support, structural elements connected to the building is not recommended for
I Category III. Where this condition cannot be avoided, the isolated footings should be con-
nected to the building 'foundation system "With grade beams.
U 7.5.7 No special subgrade 'presaturation is deemed necessary prior to placing concrete; however,
the exposed' foundation and slab subgrãde" soils should be moisture cOnditioned, as
necessary, to, maintain a moist condition as would be expected in any such concrete
placement.
7.5.8 Consideration should be given to connecting patio slabs that exceed 5 feet in width to the
building foundation to reduce the potential for future separation to occur.
7.5.9 Where buildings or other improvements are planned near the top of a slope steeper than 3:1
I (horizontal: vertical), special foundations and/or design considerations are recommended
due to the tendency for lateral soil movement to occur.
For cut and fill slopes, building footings should be deepened such that the bottom
outside edge of the footing is at least 7 feet horizontally from the face of the slope.
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Where the height of the fill slope exceeds 20 feet, the minimum horizontal distance
should be increased to H13 (where H equals the vertical distance from the top of
the slope to the toe) but need not exceed 40 feet. For composite (fill over cut)
slopes, H equals the vertical distance from the top of the slope to the bottom of the
fill portion of the slope. An acceptable alternative to deepening the footings is the
use of a post-tensioned slab and foundation system or increased footing and slab
I . reinforcement. Specific design parameters or recommendations for either of these
alternatives can be provided once the building location and fill slope geometry
have been determined.
Swimming pools located within 7 feet of the top of cut or fill slopes are not
recommended. Where such a condition cannot be avoided, it is recommended that
the portion of the swimming pool wall within 7 feet of the slope face be designed
with the assumption that the adjacent soil provides no lateral support. This
recommendation applies to fill slopes up to 30 feet in height and cut slopes
regardless of height. For swimming pools located near the top of fill slopes greater
than, 30 feet in height, additional recommendations may be required and Geocon
Incorporated should be contacted for a review Of specific site conditions.
Although- other improvements that are relatively rigid or brittle, such as concrete
flatwork or masonry walls, may experience some distress if located near the top of
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a slope, it is generally not economical to mitigate this potential. It may be possible,
however, to incorporate design measures that would permit some lateral soil
movement without causing . extensive distress. Geocon Incorporated should be
consulted for specific recommendations.
7.5.10 Exterior slabs not subject to vehicle loads shoUld be at least 4 inches thick and reinforced
with 6 x 6-W2.9 x W2.9 (6 x 6-6/6) welded wire mesh. The mesh should be placed within
the upper one-third of the slab Proper mesh positioning is critical to future performance of
the slabs. It has been our experience that the mesh must be physically pulled up into the
slab after concrete placement. The contractor should, take extra measures to provide proper
mesh placement. Prior to construction of slabs, the subgrade should be moisture
conditioned to at least optimum moisture content and compacted to a dry density of at least
90 percent of the laboratory maximum dry density.
1 7.5.11 All concrete slabs should be provided with adequate construction joints and/or expansion
joints to control unsightly shrinkage cracking. The design of joints should consider criteria
of the American Concrete Institute when establishing crack-control spacing patterns.
7.5.12 Where exterior flatwork abuts the structure at entrant or exit points, the exterior slab should I .
be dowelled into the structure's foundation stemwall. This recommendation is intended to
reduce the potential for differential elevations that could result from differential settlement
I . or minor heave of the flatwork. Dowelling details should be designed by the project
structural engineer.
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7.5.13 The recommendations of this report are intended to reduce the potential for cracking of
slabs due to expansive, soils (if present), differential settlement of deep fills, or fills of
varying, thicknesses. However, even with the incorporation of the recommendations
presented herein, foundations, stucco walls and slabs-on-grade placed on such conditions
may,.still exhibit some cracking due to soil movement and/or shrinkage. The occurrence of
concrete shrinkage cracks is independent of the supporting soil characteristics. Their
occurrence may be reduced and/or controlled by limiting the slump of the concrete, proper
concrete placement and curing, and by the placement of crack-control joints at periodic
intervals, particularly where re-entrant slab comers occur.
7.6 Retaining Walls
7.6.1 Retaining walls not restrained at the top and having a level backfill surface should be
designed for an active soil pressure equivalent to the pressure exerted by a fluid density
of -35 pounds per cubic foot (pcf). Where the backfill will be inclined at no steeper than 2
to 1, an active soil pressure of 45 pcf is recommended. These soil pressures assume that the
backfill materials within an area bounded by the wall and a 1:1 plane extending upward
from the base of the wall possess an Expansion Index of less than 90. For those lots with
finish grade soils having an Expansion Index greater than 90 and/or where backfill
materials do not conform to the above criteria, Geocon Incorporated should be consulted
for additional recommendations.
7.6.2 Unrestrained walls are those that are allowed to rotate more than 0.001H (Where H equals
the height of the retaining wall portion of the wall in feet) atthe top of the wall. Where
walls are restrained from movement at the top, an additional uniform pressure of 7H psf
should be added to the above active soil pressure. For retaining walls subjected to vehicular
loads within a horizontal distance equal to two-thirds of the wall height, a surcharge
equivalent to 2 feet soil should be added.
7.6.3 All retaining walls should be provided with a drainage system adequate to prevent the
buildup of hydrostatic forces and should be waterproofed as required by the project
architect. The use of drainage openings through the base of the wall (weep holes, etc.) is
not recommended where the seepage could be a nuisance or otherwise adversely impact the
property adjacent to the base of the wall. 'A typical retaining wall drainage system is
presented as Figure 2. The above recommendations assume a properly compacted granular
(Expansion Index less than 90) backfill material with no hydrostatic forces or imposed
surcharge load. If conditions different than those described are anticipated, or if specific
drainage details are desired, Geocon Incorporated should be contacted for additional
recommendations.
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1 7.6.4 In general, wall foundations having a minimum depth and width of one foot may be
designed for an allowable soil bearing pressure of 2,000 psf, provided the soil within 3 feet
I below the base of the wall has an Expansion Index of less than 90. The proximity of the
foundation to the top of a slope steeper than 3:1 could impact the allowable soil bearing
pressure. Therefore, Geocon Incorporated should be consulted where such a condition is
1 anticipated. The location of the retaining wall footings, however, should comply with the
recommendations presented in Section 7.5.8.
7.7 Lateral Loads
I 7.7.1 For resistance to lateral loads, an allowable passive earth pressure equivalent to a fluid
density of 300 pcf is recommended for footings or shear keys poured neat against properly
compacted granular fill soils or undisturbed natural soils. The allowable passive pressure I' assumes a horizontal surface extending at least five feet, or three times the surface
generating the passive pressure, whichever is greater The upper 12 inches of material not
I :protected by floor slabs or pavement should not be included in the design for lateral
resistance. An allowable friction coefficient of 0.4 maybe used for resistance to sliding
between soil Iandcôhcrete. This friction coefficient may be combined with the allowable
passive earth pressure when determining resistance to lateral loads.
1 7.7.2 The recommendations presented above are generally applicable to the design of rigid
concrete or masonry retaining walls having a maximum height of 8 feet. In the event that
I walls higher than 8 feet or other types of walls are planned, such as crib-type walls, Geocon
Incorporated should be consulted for additional recommendations.
7.8 Slope Maintenance
7.8.1 Slopes that are steeper than 3:1 (horizontal vertical) may, under conditions that are both 1 . difficult to prevent and predict, be susceptible to near-surface (surficial) slope instability.
The instability is typically limited to the outer three feet of a portion of the slope and
usually does not directly impact the improvements on the pad areas above or below the
slope. The occurrence of surficial instability is more. prevalent on fill slopes and is
generally preceded by a period of heavy rainfall, excessive irrigation or the migration of
subsurface seepage. The disturbance and/or loosening of the surficial soils, as might result
from root growth, soil expansion, or excavation for irrigation lines and slope planting, may
also be a significant contributing factor to surficial instability. It is therefore recommended
that, to the maximum extent practical: (a) disturbed/loosened surficial soils be either
.I removed or properly recompacted, (b) irrigation systems be periodically inspected and•
maintained to eliminate leaks and excessive irrigation, and (c) surface drains on and
adjacent to slopes be periodically maintained to preclude ponding or erosion. It should be
I
Project No. 06403-52-13 . -12-
.
June 23, 2004
noted that although the incorporation of the above recommendations should reduce the
potentil for surficial slope instability, it will not eliminat& the possibi'lity, and, therefore, it
may be necessary to rebuild or repair a portion of the project's slopes in the 'future.
7.9 Site Drainage
7.9.1 Adequate drainage is critical to reduce the potential for differential sojl movement, erosion
and subsurface seepage. Under no circum'stances should water be. allowed to pond adjacent
to footings or behind retaining walls. The site 'should be graded and maintained such that
surface drainage is directed away from structures and the top of slopes into swales or other
controlled drainage devices Roof and pavement drainage should be directed into conduits
that carry runoff away from the prpdsed structure.
7.9.2 All underground utilities should be leak free Utility and irrigation lmes should be checked
periodically for leaks fOr early :detection of water infiltration and detected leaks should be
repaired promptly. Detrimental soil movement could occur if water is allowed to infiltrate
the soil for a prolonged period of time.
7.9.3 Landscaping planters adjacent to paved areas are not recommended due to the potential for
surface Or irrigation water to infiltrate the pavement's subgrade and base course. We
recommend that 'drains to collect excess irrigation water and transmit it to drainage
structures or impervious above-grade planter boxes be used. In addition, where landscaping
is planned adjacent to the pavement, we recommend' construction of a cutoff wall along the
edge of the pavement that extends at least 6 inches below the bottom of the base material.
Project No. 06403-52-13 - 13 - June 23, 2004
I LIMITATIONS AND UNIFORMITY OF CONDITIONS
I i. Recommendations of this report pertain only to the site investigated and are based upon the
assumption that the soil conditions do not deviate from those disclosed in the investigation. If
any variations or undesirable conditions are encountered during construction, or if the 1 proposed construction will differ from that anticipated herein, Geocon Incorporated should be
notified so that supplemental recommendations can be given. The evaluation or identification.
f of the potential presence of hazardous or corrosive materials was not part of the scope of
services provided by Geocon Incorporated.
This report is issued with the understanding. that it is the responsibility of the owner, or of his
representative, to ensure that the information and recommendations contained herein are
I brought to the attention of the architect and engineer for the project and incorporated into the
plans, and that the necessary steps are taken to see that the contractor and subcontractors
carry out such recommendations in the field.
The findings of this report are valid as of the present date. However, changes in the I conditions of a property can occur with the passage of time, whether they are due to natural
processes or the works of man on this or adjacent properties. In addition, changes in
applicable or appropriate standards may occur, whether they result from legislation or the
broadening of knowledge. Accordingly, the findings of this report may be invalidated wholly
or partially by changes outside our control. Therefore, this report is subject to review and
should not be relied upon after a period of three years.
H1'
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Project No. 06403-52-13 June 23, 2004
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SOURCE: 2004 THOMAS BROTHERS MAP
SAN DIEGO COUNTY, CALIFORNIA
REPRODUCED WITH PERMISSION GRANTED BY THOMAS BORThERS MAPS. I I
THIS MAP IS COPYRIGHT BY THOMAS BROS. MAPS. IT IS UNLAWFUL TO COPY NO SCALE E OR REPRODUCE ALL OR ANY PART THEREOF, WHETHER FOR PERSONAL USE OR
RESALE, WITHOUT PERMISSION.
GEOCON
INCORPORATED (0)
GEOTECHNICAL CONSULTANTS
6960 FLANDERS DRIVE - SAN DIEGO, CALIFORNIA 92121 -2974
PHONE 858 558-6900 - FAX 858 558-6159
MCE I MM DSKIE0000
VICINITY MAP
VILLAGES OF LA COSTA - THE GREENS
NEIGHBORHOOD 1.09
CARLSBAD, CALIFORNIA
DATE 06-23-2004 1 PROJECT NO. 06403-52-13 IFIG.1
—
1.5
CONCRETE
BROWDITCH
PROPOSED s-... rrw.)rrL.T /
RETAINING WALL COMPACTED /
- BACKFILL 1
T /314
/ APPROVED
FILTER FABRIC
-
2/3 H OPEN GRADED
. 1' MAX. AGGREGATE
• 3 MAX.
GROUND SURFACE
FOOTING I 4 DIA: PERFORATED PVC
PIPE MIN. 1/2% FALL TO
APPROVED OUTLET
NO SCALE
GE000N VILLAGES OF LA COSTA-THE GREENS INCORPORATED NEIGHBORHOOD 1.09 GEOTEHNICAL CONSULTANTS
6960 FLANDERS DRIVE - SAN DIEGO,CALIFORMA 92121-2974 CARLSBAD, CALIFORNIA
PHONE 858 558-6900 FAX 858 558`16159
MCE/MM DSK/E0000 DATE 06 -2,340P4. PROJECT NO. 06403 52 13 FFIG. 2
MfT hRetni,iWl2 •
TABLE
SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS
AND FOUNDATION CATEGORY FOR
VILLAGES OF LA COSTA - THE GREENS
NEIGHBORHOOD 1.09, LOT NOS. I THROUGH 75
Approximate . Approximate .
Lot Pad Condition . Maximum Maximum Depth 'Expansion Foundation
No. Depth of Fill of Differential Fill Index Category
(feet) (feet)
.
.
1 Fill . 23 16 59 . II
2 Undercut due to 19 15 59 H cut-fill transition
3 Undercut due ° 22. 18 59 cut-fill transition
4 Fill 39. 35 59_ III
5 .Fill 64 44 :59 III
6 Fill 60 46 49 III
7 Undercut due to 24 20 49 HI cut-fill transition
8 Undercut due to
11 7 . . 49 . cut-fill transition
9 Undercut due to
. 8 4 cut-fill transition
. 49
10 Undercut due to 6 2 49 I cut-fill transition
Undercut due to
11 cut-fill transition 18 14 60 II
12 Undercut due to 29 25 60 III cut-fill transition -.
13 Udèrcut due to 31 27 60 cut-fill transition
Undercut duêto 14 cut-fill transition 32 28 60 III
Undercut due to 15 cut-fill transition 21 17 60 H
16 Undercut due to 17 13 62 II cut-fill transition
17 Undercut due to 17 13 . 62 H cut-fill transition .
. . .
18 Undercut due to 62 ' ' II cut-fill transition .
Project No. 06403-52-13 - . - June 23, 2004
(
TABLE I(Continued)
SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS
AND FOUNDATION CATEGORY FOR
VILLAGES OF LA COSTA - THE GREENS
NEIGHBORHOOD 1.09, LOT NOS. I THROUGH 75
Approximate Approximate
Lot Pad Condition Maximum Maximum Depth Expansion Foundation
No. Depth of Fill of Differential Fill Index Category
(feet) (feet)
19 Undercut due to 13 9 62 II cut-fill transition
20 Undercut dueto 14 9 62 II cut-fill transition.
21 Undercut due to 1 62 II cut-fill transition
22 Undercut due to 1 62 II cut-fill transition
23 Cut N/A N/A 37. I
24 . Cut N/A N/A 37 I
25 Cut N/A N/A . 37
26 Undercut due to 1 56 II claystone
27 Undercut due to 1 56 H claystone
28 Undercut due to 1 56 II claystone
29 Undercut due to 1 65 II claystone
30 Undercut due to 1 65 II claystone
31 Cut N/A N/A 17 I
32 Cut N/A N/A 17 I
33 Cut N/A N/A 17 I
34 Cut N/A N/A 17 I
35 Cut N/A N/A 17 I
36 Undercut due to 21 17 65 II cut-fill transition . . .
37 Undercut due to 22 18 . 38 II cut-fill transition '
38 Undercut dueto 10 6 38 I cut-fill transition
Project No. 06403-52-13 . . . June 23, 2004
TABLE I (Continued)
SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS
AND FOUNDATION CATEGORY FOR
VILLAGES OF LA COSTA - THE GREENS
NEIGHBORHOOD 1.09, LOT NOS. I THROUGH 75
Approximate Approximate
Lot Pad Condition Maximum Maximum Depth Expansion Foundation
No. Depth of Fill of Differential Fill Index Category
(feet) (feet)
39 Undercut due to 15 11 38 II cut-fill transition
40 Under due to 15 11 38 H cut-fill transition
41 Undercut due to 15 11 85 II cut-fill transition -
42 Undercut due to 15 11 '85 II cut-fill transition
Undercut due to 43 cut-fill transition 17 •'- ' - 13 85 II
Undercut due to.44 13 9 85 II cut-fill transition
45 'Undercut due to 21 17 56 H cut/fill transition
46 Undercut due to 21 17 56 H cut/fill transition
47 Undercut due to 21 17 56 H cut/fill transition
48 Undercut due to 21 17 56 H cut/fill. transition
49 Cut N/A N/A 100
50 Cut N/A N/A -100 III
51 Cut N/A N/A 100 III
52 Cut N/A ' N/A 100 III
53 Undercut due to 27 24 , 37 III cut-fill transition
54 Undercut,dueto 19 15- :37 ' H cut-fill, transition --
55 Cut N/A - N/A ' - 41 ' I
56 Cut N/A N/A 41 - I
57 Cut N/A N/A 41 I
58 Cut , N/A N/A ' 41 - I
59 Cut N/A - N/A 41 I
Project No. 06403-52-13 -
-
June 23, 2004
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1 1
1
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TABLE I (Continued),
SUMMARY OF AS-G,RADED'BUILDING PAD CONDITIONS
AND FOUNDATION CATEGORY FOR
VILLAGES OF, LA COSTA'— THE GREENS
NEIGHBORHOOD '1.09, LOT'NOS.I THROUGH 75
Approximate Approximate. '
Lot . ' Pad Condition
Maximum Maximum Depth Expansion Foundation
No. ' , Depth of Fill of Differential Fill Index Category
'(feet) (feet)
60 Undercut due to 6 ' 2 50 I cut-fill fransition
'61 Undercut due to 24 ' 20 ' 50 in cut-fill transition
62 Undercut due to 20 16 ' 50 H cut-fill transition'
Undrcut'due to 63 1 50 I concretions
Undercut due to 64 , ' 1 50 I concretions
65 Undercut due to
. ' 1 so i concretions
66 Cut N/A N/A 70 " ' II
67 Cut N/A N/A ' 70 II
68 , Cut N/A 'N/A 70 II
69 Cut N/A N/A ' 84' II
70 Cut ' N/A N/A 84 II
71 Cut N/A N/A ' 84 ' ,II
72 Cut.' , , N/A N/A '' 54 II
73 Cut' N/A ' N/A ., , ' 54 'II
74 Cut N/A NIA1. 54 II
75 Cut N/A ' N/A' ' 54 II
Project No. 06403-52-13 ' June 23, 2004
TABLE II
SUMMARY OF LABORATORY WATER-SOLUBLE SULFATE TEST RESULTS
CALIFORNIA TEST NO. 417
Sample
No.
( Water-Soluble Sulfate (/o) Sulfate Exposure
UBC Table 19-A-4
EPASB 0.021 Negligible
El-AC 0.108 Moderate
El-AD 0.210 Severe'
El-CA • 0.600 • Severe
El-CC 0.510 Severe
El-CE • 0.345 • Severe -
EI-CG • 0.615 - Severe
EI-CK 0.435 • Severe
El-CM • • 0.600 - Severe
N
Project No. 06403-52-13 - June 23, 2004