HomeMy WebLinkAboutPUD 04-13A; LA COSTA GREEN; UPDATE GEOTECHNICAL REPORT; 2006-01-13UPDATE
GEOTECHN1CAL REPORT
VILLAGES OF LA COSTA
THE GREENS - PHASE 2
NEIGHBORHOOD 1.07
LOTS I THROUGH 71
CARLSBAD, CALIFORNIA
PREPARED FOR
K. HOVNANIAN COMPANIES
SOLANA BEACH, CALIFORNIA
RECEIVED
SEP 25 2006
ENGINEERING
DEPARTMENT
JANUARY 13, 2006 L
PROJECT NO. 06403-52-24
çus c-'7Lfr))
J
GEOCON
INCORPORATED
GEOTECI-INICAL CONSULTANTS
Project No. 06403-52-24
January 13, 2006
K. Hovnanian Companies
420 Stevens Avenue, Suite 170
Solana Beach, California 92075
Attention: Mr. Jim Norum
Subject: VILLAGES OF LA COSTA - THE GREENS, PHASE 2
NEIGHBORHOOD 1.07, LOTS I THROUGH 71
CARLSBAD, CALIFORNIA
UPDATE GEOTECHNICAL REPORT
Gentlemen:
In accordance with your authorization of our Proposal No. LG-05552 dated December 30, 2005, 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
- •- - - -
Shane Rodacker
RCE 63291
12 NAL
(6/del) Addressee A.
(1/del) Gouvis Engineering
Attention: Mr. Huan Nguyen
(1/del) K Hovnanian Homes
Attention: Ms. Nehad K. Hindi
(2) Real Estate Collateral Management Company
C/0 Morrow Development
Attention: Mr. Tim O'Grady
6960 Flanders Drive U San Diego, California 92121-2974 U Telephone (858) 558-6900 U Fox (858) 558-6159
Michael C. rtwine
Senior Staff Geologist
MCE:AS: SR:dmc
/ 1-
/
TEG 1778
co No. 63291
l Exp. 6/30/08 jg;,
OF r
civil-
TABLE OF CONTENTS
PURPOSE AND SCOPE .1
PREVIOUS SITE DEVELOPMENT .............................................................................................. 1
SITE AND PROJECT DESCRIPTION ........................................................................................... 1
SOIL AND GEOLOGIC CONDITIONS ........................................................................................2
4.1 Compacted Fill (Qcf).............................................................................................................2
4.2 Alluvium (Qal) ......................................................................................................................2
4.3 Terrace Deposits (Qt)............................................................................................................2
4.4 Santiago Formation (Ts)........................................................................................................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.......................................................................................................................13
LIMITATIONS AND UNIFORMITY OF CONDITIONS
Figures:
Vicinity Map
Typical Retaining Wall Drain Detail
Tables:
Summary of As-Graded Building Pad Conditions and Foundation Category
Summary of Finish Grade Expansion Index Test Results
Summary of Laboratory Water-Soluble Sulfate Test Results
UPDATE GEOTECHNICAL REPORT
1. PURPOSE AND SCOPE
This report presents the results of the update geotechnical study for the proposed residential
development of Neighborhood 1.07, Lots 1 through 71 and associated improvements located in
Phase 2 of the Villages of La Costa - The Greens development. The site is situated north of the
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:
Update Soil and Geological Investigation, Volume I and II, 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 1.07, Lots 1 through 71, 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
71 single-family residential lots and associated streets. Fill and cut slopes were created with design
inclinations of 2:1 (horizontal:vertical) or flatter, with a maximum height of approximately 40 feet.
The maximum thickness of the compacted fill soils is approximately 71 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 1.07 consists of 71 single-family residential homes
and associated improvements. Compacted fill soils are exposed at grade and underlain by the
Santiago Formation, Terrace Deposits, and alluvium. The Santiago Formation is also exposed at
grade on cut slopes and within some roadways. The "As-Graded" Geologic Map for the project is
Project No. 06403-52-24 - 1- January 13, 2006
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 fine sands
and sandy to silty 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, alluvium, and compacted fill soils underlie the site. The
predominant materials within 4 feet of grade consist of clayey sand to silty 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, sandy clay and silty sand. The
maximum fill thickness is approximately 71 feet. Fill soils were placed in conjunction with the
observation and testing services of Geocon Incorporated, which are summarized in the above-
referenced final report of grading. The compacted fill soils are considered suitable to provide
adequate support for the proposed development.
4.2 Alluvium (Qal)
A portion of the southwestern margin of Neighborhood 1.07 along Poinsettia Lane is underlain by
alluvium (beneath the compacted fill materials); due to the presence of a shallow groundwater table
and the close proximity of the existing roadway embankment, complete removal of alluvium was not
practical and some alluvium was left in place. Consequently, a surcharge and settlement monitoring
program was implemented. Settlement data presented in final report of grading represents measured
vertical movement in the field. Based on the survey measurements, it is our opinion that the primary
settlement was essentially complete after 124 days and the area is suitable to provide support for the
proposed development.
4.3 Terrace Deposits (Qt)
Stream-deposited Terrace Deposits were exposed within cleanouts in localized portions of
Neighborhood 1.07. 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.
Project No. 06403-52-24 -2- January 13, 2006
4.4 Santiago Formation (Is)
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, underlies the
compacted fill at the site and are considered suitable for the support of the proposed development.
S. 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 nature of the Santiago Formation,
which consists of interbedded sandstone and claystone/siltstone, seepage was encountered in several
cut slopes and mitigated by 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 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 Credible seismic event of
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, etal. (1997) acceleration-attenuation relationship.
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
seismic impact to the site.
Project No. 06403-52-24 -3 - January 13, 2006
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 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
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
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) currently adopted 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, the fine-grained characteristic of the alluvium, and the additional
consolidation from the loading induced by the compacted fill, the potential for liquefaction occurring
at the site is considered to be very low.
Project No. 06403-52-24 - 4 - January 13, 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
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 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 Profile Type UBC Reference
Sc So
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 I6-T
Seismic Source B B Table 16-U
Project No. 06403-52-24 - 5 - January 13, 2006
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.
a
TABLE 7.2.2
SUMMARY OF SOIL PROFILE TYPE
Unit Lot Nos. UBC Classification
1.07 1 through 4 SD
1.07 5 through 9 Sc
1.07 10 through 24 SD
1.07 25 through 27 Sc
1.07 28 through 35 SD
1.07 36 and 37 SC
1.07 38 through 62 SD
1.07 62 Sc
1.07 63 through 71 SD
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 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
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 neighborhoods were subjected to
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
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. The
results of the soluble-sulfate tests are summarized on Table III. Table 7.3 presents a
summary of concrete requirements set forth by UBC Table 19-A-4
Project No. 06403-52-24 - 6 - January 13, 2006
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
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. 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
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 III: Fill thickness exceeds 50 feet, or variation in fill thickness exceeds 20
feet, or Expansion Index exceeds 90 but is 130 or less, or underlain by
alluvium.
Project No. 06403-52-24 - 7 - January 13, 2006
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 (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 the following table 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 in
Thomthwaite 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. 4.74 in.
Project No. 06403-52-24 - 8 - January 13, 2006
7.5.3 UBC Chapter 18, Div. III, §1816 uses interior stiffener beams in its structural design
procedures. If the structural engineer proposes a post-tensioned foundation design method
other than IJBC Chapter 18, Div. ifi, §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 III.
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 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.
7.5.5 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
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
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.
7.5.6 Foundations for Category I, II or III may be designed for an allowable soil bearing pressure
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.
7.5.7 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 III.
Where this condition cannot be avoided, the isolated footings should be connected to the
building foundation system with grade beams.
7.5.8 No special subgrade presaturation is deemed necessary prior to placing concrete; however,
the exposed foundation and slab subgrade soils should be moisture conditioned, as
necessary, to maintain a moist condition as would be expected in any such concrete
placement.
Project No. 06403-52-24 - 9 - January 13, 2006
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 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 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
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.
7.5.11 Exterior slabs not subject to vehicle loads should be at least 4 inches thick and reinforced
with 6x6-W2.91W2.9 (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
conditioned to at least optimum moisture content and compacted to at least 90 percent of
the laboratory maximum dry density.
Project No. 06403-52-24 _10- January 13, 2006
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 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 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 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) at the 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.
Project No. 06403-52-24 - 11 - January 13, 2006
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.
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
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 soils or undisturbed natural soils. The allowable passive pressure
assumes a horizontal surface extending at least 5 feet or three times the surface 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 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
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.
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.
Project No. 06403-52-24 - 12 - January 13, 2006
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.
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 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 noted that although the
incorporation of the above recommendations should reduce the 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
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 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. 06403-52-24 - 13 - January 13, 2006
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.
Project No. 06403-52-24 January 13, 2006
DR
....... ..... gsys%A 1A /
WY
Ay 16 PS PARK
9201 O KEYSTO
31~
olow"I
J / I
CARLSBAD
18 RACEWAY DIP vPJ
q /
/ DALfl I 2S0 aR k,, TIGER -_-_.---- . HAWK CT >-
Rn LA
EWAY
RD P. 4 / fl ILETtM j KU
GARDEN 'I.'
ES p ç,8D
4JV4D1SE EST 0 IND
8 L /DELVh ;EE H2 "I I s.— cq. PAWS AU4IAJV 4/
PASEO CASES .
4/ I,'VIA TEATSro Q.
E.$' VIA SIMPATIA
CT
(_)IJ
!r : SIT 7 EQ POSED VAUA I
j 5EA '\
if R06-
"
_• -
' HIS7ORIC I
- - - - -
.
--==
£'
CON 0R u
PA
RANLIiU ITT--
S 7 EL PATO - (TARR1
1 VIA P TIE/tA
RAHCH01O9J1 (1
As
5ki ST
LA COSTA ST R
f4 -09
CORTE
Fl-
C)
IIA
LD
NL
3 VIA ESTRADA C5 4 VIA
4W
ST
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 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
MCE / RA DSK/GTYPD
VA/y Mp
I VICINITY MAP I
VILLAGES OF LA COSTA - THE GREENS
NEIGHBORHOOD 1.07
CARLSBAD, CALIFORNIA
I DATE 1-13-2006 I PROJECT NO. 06403-52-24 IFIG. 1 I
PROPOSED
RETAINING WALL
CONCRETE LINE
DRAINAGE DITCH
GROUND SURFACE
R
1.5
I
LV /
COMPACTEDN / Ii
GROUND SURFACE
•
- . :• . / MIRAFI 140 FILTER
FABRIC OR EQUIVALENT
-
2/3 H ... OPEN GRADED 1 MAX.
I - . AGGREGATE
-
3MAX.
1 .... I
FOOTING t 4 DIA. PERPORATED PVC
PIPE MIN. 1/2% FALL TO
E I APPROVED OUTLET
NO SCALE
I RETAINING WALL DRAIN DETAIL I
GE000N 40) INCORPORATED
GEOTECHNICAL CONSULTANTS
6960 FLANDERS DRIVE - SAN DIEGO, CALIFORNIA 92121-2974
PHONE 858 558-6900 - FAX 858 558-6159
MCE / RA I I DSKIGTYPD
X/1_D€TAJL/REIWALLI/DWG
VILLAGES OF LA COSTA - THE GREENS
NEIGHBORHOOD 1.07
CARLSBAD, CALIFORNIA
DATE 1-13-2006 I PROJECT NO. 06403-52-24 1 FIG.2
TABLE I
SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS
AND FOUNDATION CATEGORY
FOR NEIGHBORHOOD 1.07
LOT NOS. I THROUGH 71
Lot
No. Pad Condition
Approximate
Maximum
Depth of Fill
(feet)
Approximate
Maximum Depth
of Differential Fill
(feet)
Expansion
Index
Foundation
Category
1 Fill 36 24 87 III
2 Fill 23 9 87 II
3 Fill 21 8 87 II
4 Fill 21 16 61 11
Undercut due to 4 Cut/Fill Transition
1 85 II
6
Undercut due to 5
Cut/Fill Transition
2 91 III
7 Undercut due to 5 Cut/Fill Transition
2 63 II
8 Undercut due to 16 Cut/Fill Transition
13 63 II
9 Undercut due to 6 Cut/Fill Transition
2 63 II
10 Fill 35 32 105 III
11 Fill 41 22 105 III
12 Fill 41 11 105 III
13 Fill 44 14 105 III
14 Fill 44 16 64 II
15 Fill 41 18 64 II
16 Fill 31 26 64 III
17 Fill 57 34 75 III
18 Fill 69 25 75 III
19 Fill 71 16 75 III
20 Fill 66 11 48 III
21 Fill 59 2 48 III
22 Fill 46 6 48 II
23 Fill 39 12 48 II
24 Fill 25 12 60 II
25 Fill 13 6 60 II
26 Undercut due to
Cut/Fill Transition 7 1
4 60 II
Project No. 06403-52-24 January 13, 2006
TABLE I (Continued)
SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS
AND FOUNDATION CATEGORY
FOR NEIGHBORHOOD 1.07
LOT NOS. I THROUGH 71
Lot
No. Pad Condition
Approximate
Maximum
Depth of Fill
(feet)
Approximate
Maximum Depth
of Differential Fill
(feet)
Expansion
Index
Foundation
Category
27 Undercut due to
Cut/Fill Transition 4 1 60 II
28 Fill 30 27 58 III
29 Undercut due to 24 Cut/Fill Transition
21 58 III
30
Undercut due to 22
Cut/Fill Transition
19 58 II
31 Undercut due to
Cut/Fill 24 21 _Transition
58 III
32 Undercut due to 28 Cut/Fill Transition
25 58 III
33 Fill 28 12 63 II
34 Fill 29 16 63 II
35 Fill 29 18 63 II
36
Undercut due to 17
Cut/Fill Transition
14 67 II
37 Undercut due to 9 Cut/Fill Transition
6 67 II
38 Fill 27 24 59 III
39 Fill 26 4 59 II
40 Fill 36 15 59 II
41 Fill 33 20 59 III
42 Fill 36 27 67 III
43 Fill 34 27 67 III
44 Fill/Alluvium 31 3 67 III
45 Fill/Alluvium 27 3 67 III
46 Fill/Alluvium 26 2 67 III
47 Fill/Alluvium 25 2 50 111
48 Fill/Alluvium 22 1 50 III
49 Fill 23 3 50 II
50 Fill 36 7 62 II
51 Fill 46 5 62 II
52 Fill 40 4 62 II
53 Fill 28 1 62 II
Project No. 06403-52-24 January 13, 2006
TABLE I (Continued)
SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS
AND FOUNDATION CATEGORY
FOR NEIGHBORHOOD 1.07
LOT NOS. I THROUGH 71
Approximate Approximate
Lot Maximum Maximum Depth Expansion Foundation
No. Pad Condition Depth of Fill of Differential Fill Index Category
(feet) (feet)
54 Fill 33 7 73 II
55 Fill 34 12 73 II
56 Fill 35 16 73 II
57 Fill 38 23 73 III
58 Fill 35 20 69 111
59 Fill 33 20 69 III
60 Fill 29 18 69 II
61 Undercut due to 20 17 69 II Cut/Fill Transition
62 Undercut due to 11 8 77 II Cut/Fill Transition
63 Undercut due to 24 20 77 III Cut/Fill Transition
64 Undercut due to 39 36 77 Ill Cut/Fill _Transition
65 Undercut due to 41 37 77 III Cut/Fill Transition
66
Undercut due to 25 22 77 III
Cut/Fill Transition
67
Undercut due to 29 26 98 III
Cut/Fill Transition
68
Undercut due to 29 26 98 III
Cut/Fill Transition
69
Undercut due to 31 28 98 III
Cut/Fill Transition
70 Undercut due to 30 27 32 III Cut/Fill Transition
71 Undercut due to 28 25 32 III Cut/Fill Transition
Project No. 06403-52-24 January 13, 2006
TABLE II
SUMMARY OF FINISH GRADE EXPANSION INDEX TEST RESULTS
VILLAGES OF LA COSTA; THE GREENS, NEIGHBORHOOD 1.07, LOTS I THROUGH 71
Lot Numbers Sample at Finish Grade
Expansion
Index
UBC
Classification
1 through 3 El-E 87 Medium
4 El-Fa 61 Medium
5 EI-Fb 85 Medium
6 El-Fe 91 High
7 through 9 EI-G 63 Medium
10 through 13 EI-X 105 High
14 through 16 El-Y 64 Medium
17 through 19 El-P 75 Medium
20 through 23 EI-O 48 Low
24 through 27 El-N 60 Medium
28 through 32 EI-W 58 Medium
33 through 35 El-V 63 Medium
36 and 37 El-U 67 Medium
38 through 41 EI-T 59 Medium
42 and 43 El-U 67 Medium
44 through 46 El-S 62 Medium
47 through 49 El-R 50 Low
50 through 53 E1-J 62 Medium
54 through 57 El-I 73 Medium
58 through 61 El-H 69 Medium
62 through 66 El-K 77 Medium
67 through 69 EI-L 98 High
70 and 71 EI-M 32 Low
Project No. 06403-52-24 January 13, 2006
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-E 0.096 Negligible
El-Fa 0.495 Severe
Ei-Fb 0.120 Moderate
El-Fe 0.255 Severe
EI-G 0.090 Negligible
El-H 0.675 Severe
El-1 0.540 Severe
E1-J 0.735 Severe
El-K 0.465 Severe
EI-L 0.500 Severe
El-M 0.630 Severe
El-N 0.210 Severe
El-0 0.705 Severe
El-P 0.645 Severe
El-R 0.360 Severe
El-S 0.600 Severe
EI-T 0.405 Severe
El-U 0.435 Severe
El-V 0.255 Severe
El-W 0.280 Severe
EI-X 0.048 Negligible
EI-Y 0.405 Severe
Project No. 06403-52-24 January 13, 2006