HomeMy WebLinkAboutCT 04-16; LA COSTA GREENS NEIGHBORHOOD 1.06; GEOTECHNICAL REPORT; 2006-03-10UPDATE
GEOTECHNICAL REPORT
VILLAGES OF LA COSTA
THE GREENS - PHASE 2
NEIGHBORHOOD 1.06
CARLSBAD, 'CALIFORNIA
PREPARED FOR
DAVIDSON COMMUNITIES
DEL MAR, CALIFORNIA
MARCH 10, 2006
PROJECT NO. 06403-52-25
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GEOCON
C. INCORPORATED
GEOTECHNICAL CONSULTANTS
41i~>
Project No. 06403-52-25
I March 10, 2006
Davidson Communities
1302 Camino Del Mar
Del Mar, California 92014
Attention: Ms. Brandy Alvarez
Subject: VILLAGES OF LA COSTA - THE GREENS, PHASE 2
NEIGHBORHOOD 1.06
CARLSBAD, CALIFORNIA
UPDATE GEOTECHNICAL REPORT
Dear Ms. Alvarez:
In accordance with your authorization of our Proposal No. LG-06014 dated January 23, 2006, 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,
GEO CON INCORPORATED
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Li
Michael C. Ertwine Shane Rodacker
C. Senior Staff Geologist CEG 1778 RCE 63291
MCE:AS:SR:dmc
C (6/del) Addressee
(2) Real Estate Collateral Management Company
% Morrow Development
Attention: Mr. Tim O'Grady
L
6960 Flanders Drive • San Diego, California' 92121-2974 • Telephone (858) 558-6900 U Fax (858) 558-6159
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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 Terrace Deposits (Qt) ............................................................................................................2
4.3 Previously Compacted Fill (Qpf)...........................................................................................2
r 4.4
5.
Santiago Formation (Ts) ........................................... .............................................................
GROUNDWATER ...........................................................................................................................3
2
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 ..............................................................................................................13
7.9 Site Drainage .......................................................................................................................13
LIMITATIONS AND UNIFORMITY OF CONDITIONS
FIGURES:
Vicinity Map
Typical Retaining Wall Drain Detail
TABLES:
I. Summary of As-Graded Building Pad Conditions and Foundation Category
H. Summary of Finish Grade Expansion Index Test Results
M. Summary of Laboratory Water-Soluble Sulfate Test Results
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UPDATE GEOTECHNICAL REPORT
1. PURPOSE AND SCOPE
L. This report presents the results of the update geotechnical study for the proposed residential
-. development of Neighborhood 1.06, Lots 1 through 92 and associated improvements located in
I Phase 2 of the Villages of La Costa - The Greens development. The site is situated north of Poinsettia
Lane, east of Alicante Road, and west of the adjacent Bressi Ranch development (see Vicinity Map,
[ 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 of the following:
[ 1. Update Soil and Geological Investigation, Volume I and 11, Villages of La Costa - The
Greens, Carlsbad, California, prepared 'by Geocon Incorporated, 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, NeighborhoOds 1.06 and 1.07, Carlsbad, California, prepared by
[ , Geocon Incorporated, dated December 29, 2005. (Project No. 06403-52-19B).
Grading and Erosion Control Plans for: La Costa Greens Neighborhood 1.06 & 1.07,
prepared by Hunsaker and Associates, City of Carlsbad approval dated May 10, 2005.
2. PREVIOUS SITE DEVELOPMENT
[ Neighborhood 1.06, Lots 1 through 92, was graded to finish-pad configuration during mass grading
operations for Phase 2 of The Greens development. Grading was 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 grading are presented in the above-referenced
[ report of grading. Mass grading for the subject area has been completed and consisted of developing
L 91 single-family residential lots, associated streets, and a recreation pad (Lot 44). Fill and cut slopes
were created with design inclinations of 2:1 (horizontal: vertical) or flatter, with a maximum height of
L.. approximately 40 feet. The maximum thickness of the compacted fill soil is approximately 64 feet.
An "As-Graded" Geologic Map is provided in the above-referenced report and depicts the existing
[ geologic conditions and topography.
3. SITE AND PROJECT DESCRIPTION
The development of The Greens - Neighborhood 1.06 consists of 91 single-family residential homes,
S associated improvements, and a recreation pad (Lot 44). Compacted fill soil is exposed at grade and
L. underlain by the Santiago Formation and Terrace Deposits. The Santiago Formation is also exposed
at grade on cut slopes, cut pads, and within some roadways. The "As-Graded" Geologic Map for the
Project No. 06403-52-25 - 1- March 10, 2006
project is included in the above-referenced final report of 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 consist of
silty to clayey sands and sandy clay.
The locations and descriptions of the site and proposed improvements are based on a site
[ reconnaissance, a review of the referenced grading plans, and our understanding of project
development. If 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, Terrace Deposits, previously placed compacted fill, and compacted fill soil
underlie the site. The predominant materials within 3 feet of grade consist of silty to clayey sand and
[ possess a low to high expansion potential. The soil types and geologic unit are discussed below.
[ 4.1 Compacted Fill (Qcf)
In general, the fill materials consist of light yellowish brown, silty to clayey sand. The maximum fill
[ thickness is approximately 64-feet. Fill soil was placed in conjunction with the observation and
testing services of Geocon Incorporated, which are summarized in the above-referenced final report
r of grading. The compacted fill soil is considered suitable to provide adequate support for the
L proposed development.
4.2 Terrace Deposits (Qt)
r Stream-deposited Terrace Deposits were exposed within cleanouts in localized portions of
L Neighborhood 1.06. The Terrace Deposits generally consisted of medium dense to dense, silty to
clayey sandstone and are considered suitable for the support of the proposed development.
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4.3 Previously Compacted Fill (Qpf)
These soils were placed during the grading of Bressi Ranch in conjunction with testing and
observation services provided by Leighton and Associates. These materials exist beneath compacted
fill on Lots 74 through 81. In general, the previously placed fill is competent and provides suitable
support for the proposed development.
[ 4.4 Santiago Formation (Ts)
The Eocene-age Santiago Formation, consisting of dense, massive, white to light green, silty, fine to
coarse sandstones and hard, greenish-gray to brown claystones and siltstones, is exposed at finish
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Project No. 06403-52-25 - 2 - March 10, 2006
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grade on cut lots and underlies the compacted fill at the site and is considered suitable for the support
of the proposed development.
ii 5. GROUNDWATER
Groundwater was encountered during grading operations in the alluvial soils but is not anticipated to
adversely impact the development of the property. Due to the variable nature of the Santiago
Formation, which consists of interbedded sandstone and claystone/siltstone, seepage was encountered
in several cut slopes and subsequently mitigated during remedial grading by the construction of
drained 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,
L and land use, among other factors, and vary as a result. Proper surface' drainage of irrigation and
rainwater will be important to future performance of the project.
- 6. GEOLOGIC HAZARDS
[ 6.1 Faulting and Seismicity -
Our review of pertinent geologic literature, the previously referenced geotechnical investigation
[ report dated June 25, 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 within the site.
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,
which lies approximately 22 miles to the southwest. Portions of the Rose Canyon Fault have been
included in a Special Study Earthquake Fault Zone. A maximum seismic event of Magnitude 7.2 is
postulated for the Rose Canyon Fault with an estimated maximum peak site acceleration of 0.32 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
L , California and northern Baja California region. Table 6.1 lists the fault zones that present the greatest
seismic impact to the site.
Project No. 06403-52-25 - 3 - March 10, 2006
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TABLE 6.1
FAULT SYSTEMS WITHIN THE SOUTHERN CALIFORNIA AND
NORTHERN BAJA CALIFORNIA REGION
Fault Name Distance from Site
(miles)
Maximum
Earthquake
Maximum Site
Acceleration (g)
Rose Canyon 7 7.2 0.32
Newport-Inglewood (Offshore) 10 7.1 0.25
Coronado Banks Fault Zone 22 7.6 0.17
Elsinore-Julian 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
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In the event of a major earthquake along any of the above-referenced faults or other faults in the
F southern California region, the site could be subjected to moderate to severe ground shaking. With
L 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 recomrñend that seismic design of structures be
F - performed in accordance with the Uniform Building Code (UBC) currently adopted by the City of
L Carlsbad. • -
6.2 Liquefaction
1 Liquefaction typically occurs when a site is located in a zone with seismic activity, onsite soil is
cohesionless, groundwater is encountered within 50 feet of the surface, and soil relative densities are
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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 lack of permanent groundwater table, the
potential for liquefaction occurring at the site is considered to be very low.
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Project No. 06403-52-25 - 4 - March 10, 2006
7. CONCLUSIONS AND RECOMMENDATIONS
7.1 General
7.1.1 No soil or geologic conditions were encountered during previous geotechnical
investigations 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
soil and formational materials 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 7 miles wet 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 IJBC Reference
Sc 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
Project No. 06403-52-25 - 5 - March 10, 2006 -
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7.2.2 Based on a 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 seismic design parameters as
indicated in the following table.
TABLE 7.2.2
SUMMARY OF SOIL PROFILE TYPE
Lot Nos. UBC Classification
l through 8 S0
9 through 33 Sc
34 SD
35 through 39 Sc
40 through 44 SD
45 through 67 Sc
68 and 69 SD
70 and 71 V S
72 through 81 SD
82 through 85 Sc V
86 through 92 SD
7.3 Finish Grade Soil Conditions
7.3.1 Observations and laboratory test results indicate that the prevailing soil conditions within
L - the upper approximately 3 feet of finish grade have an expansion 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
L placed within the upper 3 feet of pad grades, some larger rocks may exist at random
locations. In addition, concretionary lenses or layers may exist within the cut lots that may
cause difficult excavation.
7.3.3 Random samples obtained throughout the subject neighborhoods were subjected to
L water-soluble sulfate testing to evaluate the amount of water-soluble sulfates within the
finish-grade soil. 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 "moderate" to "severe" sulfate exposure ratings as defined by UBC Table 19-A-4. The
results of the soluble-sulfate tests are summarized on Table M. Table 7.3 presents a
L summary of concrete requirements set forth by UBC Table 19-A-4.
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Project No. 06403-52-25 - 6 - March 10, 2006
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1 TABLE 7.3
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
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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
L 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
L 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 soil as well as the Expansion Index (El) of the prevailing subgrade soil of a
particular building pad. Finish-grade Expansion Index test results are presented on Table II,
[ attached. The category criteria are summarized herein.
Category I: Maximum fill thickness is less than 20 feet and Expansion Index is less
L than or equal to 50.
Category II: Maximum fill thickness is less than 50 feet and Expansion Index is less
ç than or equal to 90, or variation in fill thickness is between 10 feet and 20
feet.
Category III: Fill thickness exceeds 50 feet, or variation in fill thickness exceeds 20
[ feet, or Expansion Index exceeds 90 but is 130 or less.
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Project No. 06403-52-25 -7 - March 10, 2006
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Notes:
All footings should have a minimum width of 12 inches.
Footing depth is measured from lowest adjacent subgrade. These depths apply to
both exterior and interior footings.
All interior living area concrete slabs should be at least 5 inches thick. This applies to
both building and garage slabs-on-grade.
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 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 the design criteria of the Post-Tensioning Institute (TJBC
Section 1816). Although this procedure was developed for expansive soil, 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 the Table 7.5 for the particular foundation category designated for each lot as
presented on Table I.
TABLE 7.5 -
POST-TENSIONED FOUNDATION SYSTEM DESIGN PARAMETERS
Post-Tensioning Institute (PT!)
Design Parameters
Foundation Category
i ii iii
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.l5in.
Center Lift Moisture Variation Distance 5.3 ft. 5.3 ft. 5.3 ft.
Center Lift 2.12 in. 3.21 in. 4.74 in.
Project No. 06403-52-25 - 8 - March 10, 2006
7.5.3 UBC Chapter 18, Div. ifi, §1816 uses interior stiffener beams in its structural design
procedures. If the structural engineer proposes a post-tensioned foundation design method
other than UBC Chapter 18, Div. III, §1816, the following recommendations apply:
The deflection criteria presented. in Table 7.5 are still applicable.
Interior stiffener beams be used for Foundation Categories II and ifi.
The depth of the perimeter foundation should be at least 12 inches for Foundation
Category I, 18 inches for Foundation Category II, . and 24 inches for Foundation
Category III.
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 are susceptible to excessive edge lift,
[ regardless of the underlying soil conditions, unless reinforcing steel is placed at the bottom
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- of the perimeter 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
[ S reinforcing tendons in the top of the slab, the resulting eccentricity after tensioning reduces
the ability of the system to mitigate edge lift. The structural engineer should design the
[ - foundation system to reduce the potential of edge lift occurring for the proposed structures.
r 7.5.5 During the construction of the post-tension foundation system, the concrete should be
[ placed monolithically. Under no circumstances should cold joints form between the
footings/grade beams and the slab during the construction of the post-tension foundation
[ system.
7.5.6 Foundations for Category I, II, or ifi may be designed for an allowable soil bearing
L- 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.
7.5.7 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 Category ifi.
L: Where this condition cannot be avoided, the isolated footings should be connected to the
building foundation system with grade beams.
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7.5.8 No special subgrade presaturation is deemed necessary prior to placing concrete; however,
the exposed foundation and slab subgrade soil should be moisture conditioned, as
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Project No. 06403-52-25 - 9 - March 10, 2006
necessary, to maintain a moist condition as would be expected in any such concrete
placement.
7.5.9 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.
7.5.10
7.5.11
Where buildings or other improvements are planned near the top of a slope steeper than 3:1
(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.
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.
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
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.
Exterior slabs not subject to vehicle loads should be at least 4 inches thick and reinforced
with 6x6-W2.9/W2.9 (6x6-6/6) 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
Project No. 06403-52-25 _10 - March 10, 2006
conditioned to at least optimum moisture content and compacted to at least 90 percent of
the laboratory maximum dry density.
7.5.12 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.
7.5.13 Where exterior flatwork abuts the structure at entrant or extant points, the exterior slab
should 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 or minor heave of the flatwork. Dowelling details should be designed by the
project structural engineer.
7.5.14 The recommendations of this report are intended to reduce the potential for cracking of
slabs due to expansive soil (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 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
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 soil 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) at the top of the wall. Where
I walls are restrained from movement at the top, an additional uniform pressure of 7H psf
L should be added to the above active soil pressure. For retaining walls subjected to vehicular
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Project No. 06403-52-25 - 11 - March 10, 2006
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
r 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
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presented as Figure 2. The above recommendations assume a properly compacted granular
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(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.
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
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
L 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 7.5.10.
[ 7.7 Lateral Loads
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 soil or undisturbed natural soil. The allowable passive pressure
1-• assumes a horizontal surface extending at least 5 feet or three times the surface generating
L 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 resistance. An
L 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
[ 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 (such as crib-type walls) are planned,
Geocon Incorporated should be consulted for additional recommendations.
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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.
L The instability is typically limited to the outer 3 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.
C The disturbance and/or loosening of the surficial soil, 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 soil be either removed or
properly recompacted; (b) irrigation systems be periodically inspected and maintained to
F 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 noted that although the
incorporation of the above recommendations should reduce the potential for surficial slope
L instability, it will not eliminate the possibility, and, therefore, it may be necessary to
rebuild or repair a portion of the projects slopes in the future.
[ I 7.9 Site Drainage
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
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 pavements subgrade and base course. We
ç recommend that drains to collect excess irrigation water and transmit it to drainage
L 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.
L S
Project No. 06403-52-25 - 13 - March 10, 2006
L
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
L 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
L 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
I should not be relied upon after a period of three years.
L
Project No. 06403-52-25 March 10, 2006
•.
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41 CTE TRAM SF
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'<tF i • çZ0 i!- 'LM J .
SOURCE: 2006 THOMAS BROTHERS MAP
SAN DIEGO COUNTY, CALIFORNIA
REPRODUCED WITH PERMISSION GRANTED BY THOMAS BROTHERS MAPS.
THIS MAP IS COPYRIGHT BY THOMAS BROS. MAPS. IT IS UNLAWFUL TO COPY NO SCALE OR REPRODUCE ALL OR ANY PANT THEREOF, WHETHER FOR PERSONAL USE OR •
RESALE. WITHOUT PERMISSION.
GE000N 0 INCORPORATED
GEOTECI-INICAL CONSULTANTS
6960 FLANDERS DRIVE - SAN DIEGO, CALIFORNIA 92121- 297A
PHONE 858 558-6900 - FAX 858 558-6159
MCEIRA
• • •
DSK/GTYPD
cy Mp
VICINITY MAP
VILLAGES OF LA COSTA -THE GREENS
NEIGHBORHOOD 1:06
CARLSBAD, CALIFORNIA
DATE 03-1 0-2006 PROJECT NO. 06403 - 52 -25 FIG. 1
GROUND SURFACE
1.5
CONCRETE LINE
DRAINAGE DITCH
PROPOSED
RETAINING WALL COMPACTED'\Y/ Ii
/ MIRAFII4OFILTER
'. . . FABRIC OR EQUIVALENT
4 4
2/3 H . I OPEN GRADED 1 MAX.
: AGGREGATE
-. 12 3 MAX.
GROUND SURFACE •d MIN.
FOOTING - I 4 DIA. PERPORATED PVC
PIPE MIN. 1/2% FALL TO
I APPROVED OUTLET
NO SCALE
I TYPICAL RETAINING WALL DRAIN DETAIL I
GE000N 400 INCORPORATED
GEOTECHNICAL CONSULTANTS
6960 FLANDERS DRIVE- SAN DIEGO, CALIFORNIA 92121 2974
PHONE 858 558-6900 - FAX 858 558-6159
MCE / RA DSK/GTYPD
'I_Ut FAJL/RtfWALLI
VILLAGES OF LA COSTA - THE GREENS
NEIGHBORHOOD 1.06
CARLSBAD, CALIFORNIA
DATE 03-10-2.006 IP0EcT NO. 06403-52-25 FIG.2
TABLE I
SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS
AND FOUNDATION CATEGORY
VILLAGES OF LA COSTA, THE GREENS - NEIGHBORHOOD 1.06, LOTS 1 THROUGH 92
Approximate Approximate
Lot Maximum Maximum Depth Expansion Foundation
No. Pad Condition Depth of Fill of Differential Fill Index Category
(feet) (feet)
1 Fill 44 28 49 III
2 Fill 31 15 49 II
3 Fill 41 20 49 III
4 Fill 37 23 49 III
5 Fill 32 8 30 II
6 Undercut due to 30 26 30 III Cut/Fill _Transition
7 Undercut due to 30 22 30 III Cut/FillTransition
8 Undercut due to 27 24 30 III Cut/Fill Transition
9 Undercut due to 6 2 36 - I Cut/Fill Transition
10 Undercut due to 7 4 36 I Cut/Fill Transition
11 Undercut due to 13 10 36 II Cut/Fill Transition
12 Undercut due to 5 1 36 I Cut/Fill Transition
13 Undercut due to 6 3 22 I Cut/Fill Transition
14 Undercut due to 6 2 22 I Cut/Fill Transition
15 Undercut due to 7 4 22 I Cut/Fill Transition
16 Undercut due to 9 5 22 I Cut/Fill Transition
17 Undercut due to 11 8 22 I Cut/Fill Transition
18 Undercut due to 13 11 34 II Cut/Fill Transition
19 Undercut due to 12 9 34 I Cut/Fill Transition
Project No. 06403-52-25 March 10, 2006
I
TABLE I (Continued)
SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS
AND FOUNDATION CATEGORY
VILLAGES OF LA COSTA, THE GREENS - NEIGHBORHOOD 1.06, LOTS 1 THROUGH 92
Approximate Approximate
Lot Maximum Maximum Depth Expansion Foundation
No. Pad Condition Depth of Fill of Differential Fill Index Category
(feet) (feet)
20 Undercut due to 11 7 34 I Cut/Fill Transition
21 Undercut due to 7 4 34 I Cut/Fill Transition
22 Undercut due to 7 3 • 34 I Cut/Fill Transition
23 Undercut due to 7 4 27 I
Cut/Fill Transition
24 Cut N/A N/A 27 I
25 Cut N/A N/A 27 I
26 Cut N/A N/A 27 I
27 Cut N/A N/A 39 I
28 Cut N/A N/A 39 I
29 Cut N/A N/A 39 I
30 Cut N/A N/A 39 I
31 Undercut due to 4 1 39, I Cut/FillTransition
32 Undercut due to 19 16 39 II Cut/Fill _Transition
33 Undercut due to 10 7 93 III Cut/FillTransition
34 Undercut due to 20 15 93 III Cut/Fill Transition
35 Undercut due to 14 11 93 III Cut/Fill Transition
36 Undercut due to 8 3 93 III Cut/Fill Transition
37 Undercut due to 9 6 69 II Cut/Fill Transition
38 Undercut due to 15 11 69 II Cut/Fill Transition
39 Undercut due to 11 8 69 II Cut/Fill Transition
40 Undercut due to 22 20 69 III Cut/Fill Transition
Project No. 06403-52-25 March 10, 2006
[
I
I
C
I
L
TABLE I (Continued)
SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS
AND FOUNDATION CATEGORY
VILLAGES OF LA COSTA, THE GREENS - NEIGHBORHOOD 1.06, LOTS 1 THROUGH 92
Lot
No. Pad Condition
Approximate
Maximum
Depth of Fill
(feet)
Approximate
Maximum Depth
of Differential Fill
(feet)
Expansion
Index
Foundation
Category
41 Undercut due to 22 Cut/Fill Transition
20 61 III
42 Undercut due to 35 Cut/Fill Transition
32 61 III
43 Undercut due to 35 Cut/Fill Transition
32 61 ifi
44 Fill
(Rec_Lot)
34 33 61 III
45 Cut N/A N/A 63 II
46 Cut N/A N/A 63 II
47 Cut N/A - N/A 63 II
48 Cut N/A N/A 50 - I
49 Cut N/A N/A 50 I
50 Cut N/A N/A 50 I
51 Cut N/A N/A 84 II
52 Cut N/A N/A 84 II
53 Cut N/A N/A 84 II
54 Cut N/A N/A 84 II
55 Undercut due to
Cut/Fill Transition
4 1 27 I
56 Undercut due to 4 Cut/Fill Transition
1 27 I
57 Cut N/A N/A 83 II
58 Cut N/A N/A 83 II
59 Cut N/A N/A 83 II
60 Cut N/A N/A 83 II
61 Cut N/A N/A 57 II
62 Cut N/A N/A 57 II
63 Cut N/A N/A 57 II
64 Cut N/A N/A 57 II
Project No. 06403-52-25 March 10, 2006
C
TABLE I (Continued)
SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS
AND FOUNDATION CATEGORY
VILLAGES OF LA COSTA, THE GREENS - NEIGHBORHOOD 1.06, LOTS 1 THROUGH 92
Approximate Approximate
Lot Pad Condition Maximum Maximum Depth Expansion Foundation
No. Depth of Fill of Differential Fill Index Category
(feet) (feet)
65 Undercut due to 4 1 27 I Cut/Fill Transition
66 Undercut due to 9 6 27 I Cut/Fill Transition
67 Undercut due to 10 7 55 II Cut/Fill Transition
68 Undercut due to 27 20 55 III Cut/Fill Transition
69 Fill 28 14 55 II
70 Undercut due to 16 13 55 II Cut/Fill Transition
71 Undercut due to 5 3 62 II Cut/Fill Transition
72 Undercut due to 24 21 62 III Cut/Fill Transition
73 Undercut due to 37 34 62 III Cut/Fill Transition
74 Fill 47 33 86 III
75 Fill 54 25 86 III
76 Fill 61 15 86 III
77 Fill 63 40 86 III
78 - Fill 60 42 64 III
79 Fill 56 52 64 III
80 Undercut due to 29 25 64 III Cut/Fill Transition
81 Undercut due to 20 17 64 II Cut/Fill Transition
82 Undercut due to 15 12 38 II Cut/Fill Transition
83 Undercut due to 12 9 38 I Cut/Fill Transition
84 Undercut due to 10 7 38 I Cut/Fill Transition
85 Undercut due to 13 10 38 II Cut/Fill Transition
Project No. 06403-52-25 March 10, 2006
I
[
C
TABLE I (Continued)
SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS
AND FOUNDATION CATEGORY
VILLAGES OF LA COSTA, THE GREENS - NEIGHBORHOOD 1.06, LOTS 1 THROUGH 92
Lot
No. Pad Condition
Approximate
Maximum
Depth of Fill
(feet)
Approximate
Maximum Depth
of Differential Fill
(feet)
Expansion
Index
Foundation
Category
86 Fill 23 20 60 III
87 Fill 32 20 60. III
88 Fill 40 23 60 III
89 Fill 57 26 60 III
90 Fill 64 27 64 III
91 Fill 58 15 64 III
92 Fill 50 18 64 III
Project No. 06403-52-25 March 10, 2006
Lot Numbers Sample at Finish Grade
Expansion
Index
UBC
Classification
1 through 4 El-AM 49 Low
5 through 8 El-AL 30 Low
9 through 12 El-AK 36 Low
13 through 17 EI-AJ 22 Low
18 through 22 El-Al 34 Low
23 through 26 EI-AH 27 Low
27 through 29 El-AG 39 Low
30 through 32 El-AF 39 Low
33 through 36 EI-AE 93 High
37 through 40 El-AD 69 Medium
41 through 44 EI-Z 61 Medium
45 through 47 El-AN 63 Medium
48 through 50 EI-AO 50 Low
51 through 54 El-AP 84 Medium
55 and 56 El-AS 27 Low
57 through 60 El-AQ 83 Medium
61 through 64 El-AR 57 Medium
65 and 66 El-AS 27 Low
67 through 70 EI-AV 55 Medium
71 through 73 El-AU 62 Medium
74 through 77 El-AT 86 Medium
78 through 81 EI-Q 64 Medium
82 through 85 El-AC 38 Low
86 through 89 El-AB 60 Medium
90 through 92 EI-AA 64 Medium
11
[I
L
C
I
[
TABLE II
SUMMARY OF FINISH GRADE EXPANSION INDEX TEST RESULTS
VILLAGES OF LA COSTA, THE GREENS - NEIGHBORHOOD 1.06, LOTS 1 THROUGH 92
L
L
L
Project No. 06403-52-25 March 10, 2006
r
1— TABLE III
SUMMARY OF WATER-SOLUBLE SULFATE LABORATORY TEST RESULTS
CALIFORNIA TEST 417
Sample No. Water-Soluble Sulfate (°) Sulfate Exposure
UBC Table 19-A-4
EI-Q 0.765 Severe
El-Z 0.340 Severe•
EI-AA 0.735 Severe
El-AB 0.765 Severe
El-AC 0.720 Severe
El-AD 0.495 Severe
EI-AE 0.675 Severe
El-AF 0.705 Severe
El-AG 0.735 Severe
El-AR 0.585 - Severe
El-Al 0.765 Severe
EI-AJ 0.720 Severe
El-AK 0.630 Severe
El-AL 0.630 Severe
El-AM 0.585 Severe
- El-AN 0.720 Severe
EI-AO 0.660 Severe
El-AP 0.525 Severe
EI-AQ 0.675 . Severe
El-AR 0.100 Moderate
El-AS 0.600 Severe
El-AT 0.360 Severe
El-AU 0.555 Severe
EI-AV 0.660 Severe
r
March 10, 2006