HomeMy WebLinkAboutCT 02-03; VILLAGES OF LA COSTA OAKS SOUTH; UPDATE GEOTECHNICAL REPORT; 2003-11-12UPDATE
GEOTECHNICAL REPORT
VILLAGES OF LA COSTA
THE OAKS SOUTH
NEIGHBORHOODS 3.12 AND 3.13
CARLSBAD, CALIFORNIA
c-c
PREPARED FOR
CENTEX HOMES
CARLSBAD, CALIFORNIA
NOVEMBER 12, 2003
I
I
Li
I
EW3OIo6
3o
I enea4
CEG 1778
Shane Rodacker
RCE 63291
SR:AS:JH:dmc
(6/del) Addressee
A Cobs
C'fiG 1524
JOHN
cc I NO. 1524 ••.
CERTiFIED I *
ENGINE j
GEOLOGIST,
''\ 12.314J')
FC
I 6960 Flanders Drive 0 Son Diego, California 92121-2974 a Telephone (858) 558-6900Fax (858) 558-6159
I
I GEOCON
INCORPORATED
I
I Project No. 06105-52-15
November 12, 2003
I
I Centex Homes
1815 Aston Street, Suite 101
Carlsbad, California 92008
GEOTECHNICAL CONSULTANTS
(0)
RECEIVED
JAN 15 2004j
CIT's OF CARISB'IL)
G,NEERIC DEPARTMENT
CM&I DIVISION
Attention: Mr. Chad Harris
Subject: VILLAGES OF LA COSTA - THE OAKS SOUTH
I 3.12 AND 3.13
CARLSBAD, CALIFORNIA
UPDATE GEOTECHNICAL REPORT
I Gentlemen:
I In accordance with your authorization of our Proposal No. LG-03500 dated July 11, 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 thi
I update report are followed, the site is considered suitable for construction and support of the proposed
structures and improvements as presently planned.
I Should you have any questions regarding this report, or if we may be of further service, please
contact the undersigned at your convenience.
I Very truly yours,
- GEOCON INCORPORATED
TABLE OF CONTENTS
PURPOSE AND SCOPE .................................................................................................................1
PREVIOUS SITE DEVELOPMENT ............................................................................................... 1
SITE AND PROJECT DESCRIPTION ........................................................................................... 2
SOIL AND GEOLOGIC CONDITIONS.........................................................................................2
4.1 Compacted Fill.......................................................................................................................2
4.2 Undercut Compacted Fill.......................................................................................................3
4.3 Santiago Peak Volcanics........................................................................................................3
GROUNDWATER ............ . ................................................................ .............................................. 3
GEOLOGIC HAZARDS..................................................................................................................3
6.1 Faulting and Seismicity..........................................................................................................3
6.2 Liquefaction ...........................................................................................................................4
CONCLUSIONS AND RECOMMENDATIONS...........................................................................5
7.1 General...................................................................................................................................5
7.2. Seismic Design.......................................................................................................................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 Loads .......................................................................................................................12
7.8 Slope Maintenance...............................................................................................................12
7.9 Site Drainage........................................................................................................................12
LIMITATIONS AND UNIFORMITY OF CONDITIONS
Figures:
Vicinity Map
Retaining Wall Drainage Detail
Tables:
I. Summary of As-Graded Building Pad Conditions and Foundation Category
H. Summary of Laboratory Water-Soluble Sulfate Test Results
nfl
UPDATE GEOTECHNICAL REPORT
1. PURPOSE AND SCOPE
I This report presents the results of the update geotechnical study for the proposed residential
development of Lots 1 through 91 and associated improvements located in the Villages of La Costa -
I The Oaks South Neighborhoods 3.12 and 3.13 development. The site is situated east of the adjacent
M.A.G. property, south of the SDG&E utility line easement and north of the future La Costa Avenue
I
alignment in Carlsbad, California (see Vicinity Map, Figure 1). The purpose of this update report is to
provide foundation and retaining wall design recommendations.
I The scope of the study included a review of the following:
I 1. Update Geotechnical Investigation, Villages of La Costa - The Oaks, Carlsbad, California,
prepared by Geocon Incorporated, dated August 3, 2001 (Project No. 06105-12-04).
I 2. Final Report of Testing and Observation Services Performed During Site Grading, Villages
of La Costa - The Oaks South, Neighborhoods 3.12 and 3.13, La Costa Avenue
Station 142+84 to 156+80 and Camino Junipero Station 31+00 to 39+50, Carlsbad,
I
California, prepared by Geocon Incorporated, dated November 12, 2003 (Project No. 06105-
52-06).
I
3. Grading and Erosion Control Plans for Villages of La Costa Oaks South Neighborhood 3.12
and 3.13, prepared by Hunsaker and Associates, City of Carlsbad approval dated May 1,
2003.
2. PREVIOUS SITE DEVELOPMENT
I Neighborhoods 3.12 and 3.13, Lots 1 through 91 were graded to a finish pad configuration during
mass grading operations for the Villages of La Costa - The Oaks South development. Grading was
I performed in conjunction with the observation and testing services of Geocon Incorporated. A
summary of the observations, compaction test results, and professional opinions pertaining to the
I
grading are presented in the above-referenced report of grading. Mass grading for the site has been
completed and consisted of developing 91 single-family residential lots, a passive park site and
associated streets. Fill and cut slopes were created with design inclinations of 2:1 (horizontal: vertical)'
I 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 report and
depicts the existing geologic conditions and topography.
F11
I ,
Project No. 06105-52-15 - 1- November 12, 2003
Fi
n
I
3. SITE AND PROJECT DESCRIPTION
The development of The Oaks South Neighborhoods 3.12 and 3.13 consists of 91 single-family
I
residential homes, a passive park site and associated improvements. The park site is located south of
Lot 1 in Neighborhood 3.12. Santiago Peak Volcanics and compacted fill soils are exposed at grade.
The As-Graded Geologic Map for the project is included in the above-referenced final report of
I grading. 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 onsite
I
blasting of hard metavolcanic rock to clayey fine sands, sandy to silty clay, and sandy to clayey
gravels.
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.
1 4. SOIL AND GEOLOGIC CONDITIONS
I
The site is underlain by Santiago Peak Volcanics and compacted fill soils with a maximum thickness
on the order of 65 feet. The predominant materials within 3 feet of grade consist of clayey fine sands,
sandy to silty clay, and sandy to clayey gravels and possess a very low to high expansion potential.
I The soil type and geologic unit are discussed below.
I 4.1 Compacted Fill
In general, structural fill placed and compacted at the site consisted of material which can be
I classified into three zones: (1) 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. (2) Zone B - Material placed within 10 feet from
I 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
I in roadways and parkways consisted of "soil-rock" fill with a maximum particle dimension of 12
inches. (3) 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
I dimension of approximately 8 feet were buried individually during "rock" fill grading operations.
I 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
I
report of grading. The compacted fill soils are considered suitable to provide adequate support for the
proposed development.
I
Project No. 06105-52-15 - 2 - November 12, 2003
I.
I
I
4.2 Undercut Compacted Fill
In accordance with the recommendations presented in the above-mentioned update investigation,
I
individual lots were generally undercut to a depth of 3 to 4 feet below finish pad elevation where hard
rock was exposed at grade. However, due to construction technique and equipment limitations the
undercut occasionally exceeded the recommended depth. Consequently, compacted fill depths in
I these areas can be several feet more than anticipated.
I 4.3 Santiago Peak Volcanics
Jurassic-aged Santiago Peak Volcanics comprise the majority of the underlying bedrock at the site
and are considered suitable for support of the proposed site development.
I
5. GROUNDWATER
Groundwater was not encountered during grading operations and is not anticipated to adversely
I
impact the development of the property. 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
I drainage of irrigation and rainwater will be important to future performance of the project.
I 6. GEOLOGIC HAZARDS
6.1 Faulting and Seismicity
I Our review of pertinent geologic literature, the previously referenced geotechnical investigation
report dated August 3, 2001, and our experience with the soil and geologic conditions in the general
area indicate that no known active, potentially active, or inactive faults are located at the site.
The nearest known "active" faults are the Rose Canyon Fault and the Newport-Inglewood (offshore)
I located approximately 8 and 13 miles, respectively, to the west and the Elsinore Fault Zone, which
lies approximately 23 miles to the northeast. Portions of the Rose Canyon Fault have been included in
an Alquist-Priolo Earthquake Fault Zone. A Maximum Credible seismic event of Magnitude 6.9 is
postulated for the Rose Canyon Fault with an estimated Maximum Credible peak site acceleration of
0.28 g based on the Sadigh, et al,. (1997) acceleration-attenuation relationship.
The seismicity of the site is influenced by both local and regional fault systems within the southern
I California and northern Baja California region. Table 6.1 lists the fault zones that present the greatest
seismic impact to the site.
I I
1
Project No. 06105-52-15 - 3 - November 12, 2003
H
I
I
TABLE 6.1
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 8 6.9 0.28
Newport—Inglewood (Offshore) 13 6.9 0.20
Elsinore — Julian 23 7.1 0.13
Elsinore - Temecula 23 6.8 0.11
Coronado Banks Fault Zone 23 7.4 0.16
Elsinore - Glen Ivy 38 6.8 0.06
Palos Verdes - 43 7.1 0.06
San Jacinto-Anza 46 7.2 0.06
I 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 severe ground shaking. With
respect to seismic shaking, the site is considered comparable to others in the general vicinity. While
I 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
I and the soil conditions underlying the site. We recommend that seismic design of structures be
performed in accordance with the Uniform Building Code (UBC) currently adopted by the City of
i
Carlsbad.
6.2 Liquefaction
I 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
I 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
I nature of the compacted fill and formational materials and the lack of a permanent groundwater table,
the potential for liquefaction occurring at the site is considered to be very low.
I
1
LI
Project No. 06105-52-15 - 4 - November 12, 2003
I
I
1
I
I
I
7. 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 recommenda-
tions 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 in
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 8 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 Profile Type UBC Reference
SD Sc
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
I
7.2.2 Based on review of the as-graded conditions presented in the as-graded report referenced
I above, as well as the seismic setting, the lots are assigned the seismic design parameters as
indicated below in 7.2.2.
I
Project No. 06105-52-15 - 5 - November 12, 2003
I
Li
d
1
I
I
I
I
I
Li
I
I
I
I
I
TABLE 7.2.2
SUMMARY OF SOIL PROFILE TYPE
Building Pad UBC Classification
1 SD
2 through 12 Sc
13 S0
14 Sc
15 through 26 SD
27 Sc
28 through 51 SD
52 through 66 Sc
67 SD
68 Sc
69 through 84 SD
85 Sc
86 through 91 SD
7.3 Finish Grade Soil Conditions
I 7.3.1 Observations and laboratory test results indicate that the prevailing soil conditions within
the upper approximately 3 feet of finish grade have an expansion potential of "very low" to
"high" (Expansion Index of 130 or less) as defined by Uniform Building Code (UBC)
I Table 18-I-B. Expansion Index test results for each lot are included on Table I.
I 7.3.2 It should be noted that although rocks larger than 6 inch diameter were not intentionally
placed within the upper 3 feet of pad grades, some larger rocks may exist at random
i locations.
7.3.3 Random samples obtained throughout Neighborhoods 3.12 and 3.13 were subjected to
I water-soluble sulfate testing to evaluate the amount of water-soluble sulfates within the
finish grade soils. These test results are used to determine the potential for sulfate attack on
I . 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-A-4.
Table 7.3 presents a summary of concrete requirements set forth by UBC Table 19-A-4.
1 The results of the water-soluble sulfate tests are summarized on Table II. If the concrete
used in Neighborhoods 3.12 and 3.13 does not meet the requirements for "severe" sulfate
I exposure rating, as provided in Table 7.3, additional laboratory testing should be performed
to assess the sulfate exposure of each lot.
I
Project No. 06105-52-15 - 6 - November 12, 2003
I .
I
I
I
1
I
I
I
Ll
I
TABLE 7.3
I
REQUIREMENTS FOR CONCRETE EXPOSED TO
SULFATE-CONTAINING SOLUTIONS
Sulfate Water-Soluble Cement Maximum Water Minimum
Exposure Sulfate Percent Type 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 Severe > 2.00 V 0.45 4500
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.
1 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. We understand that a post-tensioned foundation system will be
used throughout the project. Therefore, conventional foundation recommendations are not
included in this report, but can be provided upon request. A summary of the foundation
categories for each lot is presented on Table I, attached. 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.
Category Ill: Fill thickness exceeds 50 feet, or variation in fill thickness exceeds 20 feet, or
Expansion Index exceeds 90 but is less than 130.
Project No. 06105-52-15 - 7 - November 12, 2003
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
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 interior living area concrete slabs should be at least 5 inches thick.
All interior 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 covered with at least 2 inches 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 is understood
that 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 in Table 7.5 entitled Post-Tensioned Foundation Systems Design Parameters for
the particular foundation category designated.
TABLE 7.5
POST-TENSIONED FOUNDATION SYSTEM DESIGN PARAMETERS
Post-Tensioning Institute (PTI)
Design Parameters
Foundation Category
i ii in
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 2.12 in. 3.21 in. 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
Categories II and ifi. Furthermore, the depth of the perimeter foundation should be at
least 12 inches for Foundation Category I. Where the Expansion Index for a particular
I=
Project No. 06105-52-15 - 8 - November 12, 2003
I
I
I
I
LI
I
I
1
I
I
I
I
I
I
I
I
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.
I 7.5.4 Foundations for Category I, II or ifi may be designed for an allowable soil bearing pressure
of 2,000 pounds per square foot (psi) (dead plus live load). This bearing pressure may be
increased by one-third for transient loads such as wind or seismic forces.
I 7.5.5 The use of isolated footings that are located beyond the perimeter of the building
I and support structural elements connected to the building is not recommended for
Category III. Where this condition cannot be avoided, the isolated footing§ should be con-
nected to the building foundation system with grade beams.
7.5.6 No special subgrade presaturation is deemed necessary prior to placing concrete; however,
I the exposed foundation and slab subgrade soils should be sprinkled, as necessary, to
maintain a moist condition as would be expected in any such concrete placement.
7.5.7 Consideration should be given to connecting patio slabs that exceed 5 feet in width to the
I
building foundation to reduce the potential for future separation to occur.
7.5.8 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.
I 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.
Where the height of the fill slope exceeds 20 feet, the minimum horizontal distance
should be increased to H/3 (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
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.
I 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
I 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
I
Project No. 06105-52-15 - 9 - November 12, 2003
Li
I
regardless of height. For swimming pools located near the top of fill slopes greater
I than 30 feet in height, additional recommendations may be required and Geocon
Incorporated should be contacted for a review of specific site conditions.
I 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
I 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
I
consulted for specific recommendations.
7.5.9 For building pads with finish-grade soils possessing an Expansion Index of less than 90, it
I is recommended that exterior slabs should be at least 4 inches thick and reinforced with
6x 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
1 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
I mesh placement. The reinforcement for building pads with Expansion Index greater than
90 should consist of No. 3 bars at 18 inches, on center, both directions. Prior to
I construction of slabs, the subgrade should be moisture conditioned to at least optimum
moisture content and compacted to at least 90 percent of the laboratory maximum dry
density.
7.5.10 All concrete slabs should be provided with adequate construction joints and/or expansion
I joints to control unsightly shrinkage cracking. The design of joints should consider criteria
of the American Concrete Institute when establishing crack-control spacing patterns.
I 7.5.11 Where exterior flatwork abuts the structure at entrant or exit points, the exterior slab should
- be dowelled into the structure's foundation stemwall. This recommendation is intended to
I reduce the potential for differential elevations that could result from, differential settlement
or minor heave of the flatwork. Dowelling details should be designed by the project
1
structural engineer.
7.5.12 The recommendations of this report are intended to reduce the potential for cracking of
I 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
I 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
I occurrence may be reduced and/or controlled by limiting the slump of the concrete, proper
I
Project No. 06105-52-15 _10 - November 12, 2003
Li
1
I
concrete placement and curing, and by the placement of crack-control joints at periodic
intervals, particularly where re-entrant slab corners occur.
7.6 Retaining Walls
7.6.1 Retaining walls not restrained at the top and having a level backfill surface should be
1 designed for an active soil pressure equivalent to the pressure exerted by a fluid density
of 30 pounds per cubic foot (pcf). Where the backfill will be inclined at no steeper than 2
I to 1, an active soil pressure of 40 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 50. For those lots with
I finish grade soils having an Expansion Index greater than 50 and/or where backfill
materials do not conform to the above criteria, Geocon Incorporated should be consulted
I for additional recommendations.
I 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) at the top of the wall. Where
walls are restrained from movement at the top, an additional uniform pressure of 7H psf
I 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
I 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
I 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
I (Expansion Index less than 50) backfill material with no hydrostatic forces or imposed
surcharge load. If conditions different than those described are anticipated, or if specific
I drainage details are desired, Geocon Incorporated should be contacted for additional
recommendations.
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
I pressure. Therefore, Geocon Incorporated should be consulted where such a condition is
anticipated. The location of the wall footings, however, should comply with the
recommendations presented in Section 7.5.8.
I
Project No. 06105-52-15 - 11 - November 12, 2003
n
1
i
7.7 Lateral Loads
7.7.1 For resistance to lateral loads, an allowable passive earth pressure equivalent to a fluid
I 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
assumes a horizontal surface extending at least five feet, or three times the surface
I generating the passive pressure, whichever is greater. The upper 12 inches of material not
protected by floor slabs or pavement should not be included in the design for lateral
I resistance. An allowable friction coefficient of 0.4 may be used for resistance to sliding
between soil and concrete. This friction coefficient may be combined with the allowable
passive earth pressure when determining resistance to lateral loads.
7.7.2 The recommendations presented above are generally applicable to the design of rigid
I concrete or masonry retaining walls having a maximum height of 8 feet. In the event that
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.
I
7.8 Slope Maintenance
7.8.1 Slopes that are steeper than 3:1 (horizontal: vertical) may, under conditions that are both
difficult to prevent and predict, be susceptible to near-surface (surficial) slope instability.
I 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
I 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
I 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
I that, to the maximum extent practical: (a) disturbed/loosened surficial soils be either
removed or properly recompacted, (b) irrigation systems be periodically inspected and
maintained to eliminate leaks and excessive irrigation, and (c) surface drains on and
I adjacent to slopes be periodically maintained to preclude ponding or erosion. It should be
noted that although the incorporation of the above recommendations should reduce the
I potential for surficial slope instability, it will not eliminate the possibility, and, therefore, it
may be necessary to rebuild or repair a portion of the project's slopes in the future.
7.9 Site Drainage
I 7.9.1 Adequate drainage is critical to reduce the potential for differential soil movement, erosion
and subsurface seepage. Under no circumstances should water be allowed to pond adjacent
to footings or behind retaining walls. The site should be graded and maintained such that
Project No. 06105-52-15 -- -12 - November 12, 2003
I
I
I
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 proposed structure.
7.9.2 All underground utilities should be leak free. Utility and irrigation lines 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. 06105-52-15 November 12, 2003
I
LIMITATIONS AND UNIFORMITY OF CONDITIONS
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
proposed construction will differ from that anticipated herein, Geocon Incorporated should be
notified so that supplemental recommendations can be given. The evaluation or identification
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
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
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.
1
I
Project No. 06105-52-15 November 12, 2003
I
I
I
I
I
I
I
$
1 05;
E
IR
I v 'T, 1 :N 'XI
I
.
SIP,
It
14, 31
A ----------i
2009 ol
v.
CE ~~ NN WA ICA
NIP
rar
/ i
A I
DR
IIVG /
-
-510 wy
31
/ 'ESFEM / I
______
:
tI L)_1 !t — I - L 5 U
:-- _
2 - ~MINQ -Iau ..Lci\
AV.
. / '/J /L0\
It
. .' u
c. 4, IVID
i
IA COSTA
/ so CANYON
HS - .,:
c;z 4M .
WY Al I
-' ,
AWA
Mon
14 / SELIA LI &
ol --
-
AVENIDA
—
ESPER/JIZA W CAST LLOJ
'I o.Low_
c...
p-
--- — PAN1 Oo \DOUBLE ! COUNTRY ROSE
ltr
'4s
SOURCE: 2003 THOMAS BROS. MAP
SAN DIEGO COUNTY, CALIFORNIA
REPRODUCED WITH PERMISSION GRANTED BY THOMAS BROS. MAPS.
THIS MAP IS COPYRIGHT BY THOMAS BROS. MAPS. if IS UNLAWFUL TO COPY
OR REPRODUCE ALL OR ANY PART THEREOF, WHETHER FOR PERSONAL USE OR
RESALE, WIThOUT. PERMISSION.
GE000N
INCORPORATED
GEOTECHNICAL CONSULTANTS
6960 FLANDERS DRIVE - SAN DIEGO, CALIFORNIA 92121-2974
PHONE 858 558-6900 - FAX 858 558-6159
SR/ RA DSKJE0000
5eufr./Do6,g 4/W.fl IilMcn,, if te.Wrty Mop
I
i
N
NO SCALE
VICINITY MAP
VILLAGES OF LA COSTA
THE OAKS SOUTH - NEIGHBORHOODS 3.12 AND 3.13
CARLSBAD, CALIFORNIA
DATE. 11-12-2003 1 PROJECT NO. 061055215I FIG.1
GROUND SURFACE
CONCRETE
BROWDITCH
PROPOSED
RETAINING WALL COMPA
BACKFII
TED
3/4
. / MIRAFI 140 FILTER FABRIC
(OR EQUIVALENT)
(
2/3H .. OPEN GRADED
1 MAX. AGGREGATE
••.. i
5'MAX.
PROPOSED
GRADE
FOOTING t 4' DIA. PERFORATED PVC
I PIPE MIN. 1/2% FALL TO.
S APPROVED OUTLET
NO SCALE
I TYPICAL RETAINING WALL DRAIN DETAIL
GEOCON
INCORPORATED 400
GEOTECI-iNICAL CONSULTANTS
6960 FLANDERS DRIVE - SAN DIEGO, CALIFORNIA 92121- 2974
PHONE 858 558-6900 - FAX 858 558-6159
SR/AML DSKIE0000
0D1.DWG/on
VILLAGES OF LA COSTA
THE OAKS SOUTH - NEIGHBORHOODS 3.12 AND 3.13
CARLSBAD, CALIFORNIA
DATE 11-12-2003 1 PROJECT NO. 06105 -52-15 FIG. 2
TABLE I
SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS
AND FOUNDATION CATEGORY FOR NEIGHBORHOODS 3.12 AND 3.13
LOT NOS. 1 THROUGH 91, LA COSTA OAKS
Lot
No. Pad Condition
Approximate
Maximum
Depth of Fill
(feet)
Approximate
Maximum Depth of
Differential Fill (feet)
Expansion
Index Category
Foundation
1 Fill 28 17 0 II
2 Undercut due to 14
cut/fill transition
11 0 II
3 Undercut due to 6 cut/fill transition
1 0 I
4 Undercut due to rock 4 1 0 I
5 Undercut due to rock 4 1 0 I
6 Undercut due to rock 4 1 15 I
7 Undercut due to rock 4 1 15 I
8 Undercut due to rock 7 2 15 I
9 Undercut due to rock 6 1 15 I
10 Undercut due to rock 5 1 15 I
11 Undercut due to rock 5 1 15 I
12 Undercut due to rock 14 9 15 I
13 Fill 20 15 0 II
14 Undercut due to 14 cut/fill_transition 11 0 II
15 Fill 39 8 13 II
16 Fill 40 13 .13 II
17 Fill 38 12 13 II
18 Fill 39 16 - 13 II
19 Fill 38 20 0 III
20 Fill 40 17 0 II
21 Fill 30 5 0 II
22 Fill 27 7 0 II
23 Fill 29 15 0 II
24 Fill 27 21 14 III
25 Fill 20 10 14 II
26 Fill 20 12 14 II
27 Fill 18 15 14 II
28 Fill 62 17 40 III
29 Fill 61 10 40 III
30 Fill 62 6 40 III
Project No. 06105-52-15 November 12, 2003
1
I
1
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I TABLE I (Continued)
I
SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS
AND FOUNDATION CATEGORY FOR NEIGHBORHOODS 3.12 AND 3.13
LOT NOS. 1 THROUGH 91, LA COSTA OAKS
Lot
No. Pad Condition
Approximate
Maximum
Depth of Fill
(feet)
Approximate
Maximum Depth of
Differential Fill (feet)
Expansion
Index
Foundation
Category
31 Fill 61 3 40 III
32 Fill 61 5 40 III
33 Fill 58 3 28 III
34 Fill 53 5 28 III
35 Fill 57 5 28
36 Fill 60 4 28 III
37 Fill 60 4 28
38 Fill 52 8 6
39 Fill 51 10 6 III
40 Fill 53 8 6 III
41 Fill 53 6 6 III
42 Fill 50 10 6 III
43 Fill 50 10 27 III
44 Fill 33 14 27 II
45 Fill 42 18 88 II
46 Fill 41 14 113 III
47 Fill 45 25 100 III
48 Fill 47 21 73 III
49 Fill 41 17 55 II
50 Fill 27 16 81 II
51 Undercut due to 23 cut/fill transition
20 17 III
52 Undercut due to 16 cut/fill transition
13 17 II
53 Undercut due to 14
cut/fill transition
11 17 II
54 Undercut due to 18
cut/fill transition
15 17 II
55 Undercut due to
cut/fill transition 14
I
11 17 II
56 Undercut due to rock 1 4 1 1 1 21 I
I
Project No. 06105-52-15 November 12, 2003
I,
I
I,
LI
I
I
I
I
I
1
I (
Project No. 06105-52-15
I
November 12, 2003 I
I TABLE I (Continued)
I
SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS
AND FOUNDATION CATEGORY FOR NEIGHBORHOODS 3.12 AND 3.13
LOT NOS. 1 THROUGH 91, LA COSTA OAKS
Lot
Approximate
Maximum
Approximate Expansion Foundation
No.
Pad Condition Depth of Fill
Maximum Depth of Index Category
Differential Fill (feet)
(feet)
57 Undercut due to rock 4 1 21 I
58 Undercut due to rock 4 1 21 I
59 Undercut due to rock 4 1 21 I
60 Undercut due to rock 4 1 33 I
61 Undercut due to rock 4 1 33 I
62 Undercut due to 18 15 33 II
cut/fill transition
63 Undercut due to 13 10 33 II
cut/fill transition
64 Undercut due to 7 4 33 I
cut/fill transition
65 Undercut due to 4 1 0 I
cut/fill transition
66
Undercut due to 18 15 0 II
cut/fill transition
67 Undercut due to 20 17 0 II
cut/fill transition
68 Undercut due to 15 12 0 II
cut/fill transition
69 Undercut due to 24 21 _0 III
cut/fill transition
70 Undercut due to 23 20 0 III
cut/fill transition
71 Fill 36 31 22
72 Fill 35 24 22 III
73 Fill 39 35 22 III
74 Fill 24 20 22 III
75 Fill 25 22 22 III
76 Fill 30 21 8 III
77 Fill 58 38 8 III
78 Fill 54 12 8 III
79 Fill 52 35 8 III
80 Fill 49 41 8 III.
81 Fill 30 21 8 III
82 Undercut due to 40 37 0 III
cut/fill transition
I
I
I
I
I
Li
I
I
Li
I
I
I
I
I
d
TABLE I (Continued)
SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS
AND FOUNDATION CATEGORY FOR NEIGHBORHOODS 3.12 AND 3.13
LOT NOS. 1 THROUGH 91, LA COSTA OAKS
Approximate Approximate Lot Pad Condition Maximum Maximum Depth of Expansion Foundation
No. Depth of Fill Differential Fill (feet) Index Category (feet)
83 Undercut due to 37 34 0 III
cut/fill_transition
84 Undercut due to 37 34 0 ifi
cut/fill_transition
85 Undercut due to 13 10 0 II
cut/fill_transition
86 Fill 28 24 0 III
87 Fill 28 25 0 III
88 Fill 36 33 0 III
89 Fill 38 35 0 III
90 Fill 36 33 0 III
91 Fill 41 37 0 III
TABLE II
I SUMMARY OF LABORATORY WATER-SOLUBLE SULFATE TEST RESULTS
NEIGHBORHOODS 3.12 AND 3.13, LA COSTA OAKS
- CALIFORNIA TEST 417
Sample No. Water-Soluble Sulfate (%) Sulfate Exposure
S-i 0.047 Negligible
S-2 0.260 Severe
S-3 0.048 Negligible
S-4 0.031 Negligible
S-S 0.027 Negligible
S-6 0.030 Negligible
S-7 0.090 Negligible
S-8 0.090 Negligible
I ..
I I
I
Project No. 06105-52-15
I
November 12, 2003