HomeMy WebLinkAboutCT 07-05; LA COSTA GREENS NEIGHBORHOOD 1.03; INTERIM REPORT OF TESTING & OBSERVATION DURING SITE GRADING; 2009-03-26INTERIM. REPORT OF TESTING
AND OBSERVATION SERVICES
PERFORMED DURING SITE GRADING
VILLAGES OF LA COSTA
THE GREENS
NEIGHBORHOOD 1.03,
MODEL LOTS 1. THROUGH 3
CARLSBAD, CALIFORNIA
PREPARED FOR
COLRICH
SAN DIEGO, CALIFORNIA
am
MARCH 26,2009.
PROJECT NO; 06403-52-32A
GEOCO
INCORPORATED
P
GEOTECHNICAL CONSULTANTS
Project No. 06403-52-32A 0
March 26, 2009
CoiRich
4747 Morena Boulevard, Suite 100
San Diego, California 92117
Attention: Ms. Teri Shusterman
Subject: VILLAGES OF LA COSTA - THE GREENS
NEIGHBORHOOD 1.03
MODEL LOTS 1 THROUGH .3
CARLSBAD, CALIFORNIA
INTERIM REPORT OF TESTING ANDOBSERVATION SERVICES
PERFORMED DURING SITE GRADING
Dear Ms. Shusterman: -
In accordance with your recluest and our Proposal No. LG-082 12 dated June 25, 2008, we have
provided testing and observation services during the precise grading operations for the Model Lots 1
through 3 within the Villages of La Costa; The Greens, Neighborhood 1.03 development. We will
prepare a final report subsequent to the completion of grading for Lots 4 through 38. We performed our
services during the period of December 3, 2008 through March 17, 2009. The scope of our services
summarized in this report includes: I
Obseiving removal excavations during remedial grading operations, performing field mapping,
and providing geotechnical engineering consultation services,
Observing the grading operations including, the removal and/or processing of topsoil
undocumented fill, previously placed fill, alluvium, and undercutting cut lots and cut/fill
- transition lots.
Performing in-place density tests on fill placed and compacted at the site;
Performing laboratory tests to aid in evaluating the maximum dry density and optimum
moisture content and shear strength of the compacted fill. Additionally, 'we performed
laboratory tests on samples of soil present within appoximately 3 feet of finish grade to
evaluate expansion characteristics, pH, resistivity, and water-soluble sulfate content;
Preparing an Interim As-Graded Geologic Map; and
Preparing this interim report of grading;
GENERAL •
The site was previously sheet graded as part of the Villages of La Costa - The Greens, Neighborhoods
1.01 through 1.03 development. The property-is located southeast of the intersection of El Camino Real
6960 Flanders Drive • San Diego, California 92121-2974 • Telephone (858) 558-6900 • Fax (858) 558-6159
I
and Camino Vida Roble in Carlsbad, California. The Vicinity Map, Figure 1, shows the approximate
location of the subject site. -
The grading contractor for the project is American Pride Incorporated of Escondido, California. Grading
plans for the project, are entitled Rough Grading Plans for: La Costa Greens; Neighborhood 13, prepared
by Hunsaker and Associates, with City of Carlsbad approval dated November 7, 2008.
The scope of our services also included a review of:
Addendum to. Final Report of- vesting and Observation Services Performed During Site
Grading, Villages of La Costa - The Greens, Neighborhoods L02 and 1.03, Carlsbad,
California, prepared by Geocon Incorporated, dated January 3, 2007 (Project No. 06403-
52-22). .
Final Report of Testing and Observation Services Performed During Site Grading, Villages of
La Costa - The Greens, Neighborhoods 1.02 and 1.03, Carlsbad, California, prepared by
Geocon Incorporated, dated April 3, 2006 (Project No. 06403-52722).
Update Soil and Geological Investigation, Volume 1 and II, Villages of La Costa - The Greens,
Carlsbad, California, prepared by Geocon Incorporated, dated June 25, 2001 (Project
No. 06403-12-03). .
References to elevations and1ocations herein were based on surveyors' or grade checkers' stakes in the
field and interpolation from the referenced plans. Geocon Incorporated did not provide surveying
services and, therefore, has no opinion regarding the accuracy of the elevations or surface geometry
with respect to the approved plans.
GRADING
Prior to mass grading operations, the site was primarily characterized by moderately sloping hillside
terrain dissected by a series of tributary canyons that drained eastward toward San Marcos Creek. Mass
grading for the site consisted of daylight cuts and fills ,to achieve finish-grade elevations. We
performed testing and observations services during mass grading operations for the master developer.
A summary of the observations, compaction test results and 'professional opinions pertaining to the
mass grading operations are presented in the referenced reports dated April 3, 2006 and January 3,
2007. Subsequent to mass grading, the site consisted of a large sheet-graded pad with drainage
generally flowing to the southwest toward a desilting basin.
This report pertains to the grading of Lots 1 through 3 within the Neighborhood 1.03 development. The
current grading operations for the site consists of minor cut and fill operations to create 38 single-
family residential buildings with associated infrastructure. Grading began with the removal and export
of brush and vegetation from the area to be graded. Previously placed fill was scarified, moisture
conditioned as necessary, and compacted. Fill materials derived from onsite excavations and imported
Project No. 06403-52-32A - 2 - March 26, 2009
material, were then placed and compacted in layers until the design elevations were attained. In
addition, due to the existence of cut/fill transitions and/or the difficult excavation characteristics of the
formational materials, cut and cut/fill transition lots were undercut at least approximately three feet and
replaced with compacted fill to the design elevations (map symbol Quc). The resulting removal
bottoms were sloped toward the adjacent streets. Bottom elevations and the approximate limits of the
as-graded geology are presented on the Interim As-Graded Geologic Map (Figure 2).
Fill Materials and Placement Procedures
On-site and imported fill materi&ls generally consist of silty to clayey sand. We observed compaction
proëedures during grading operations and performed in-place density tests to evaluate the dry density
and moisture content of the fill material. We performed in-place density tests in general conformance
with ASTM Test Method D 2922 (nuclear). The results of the in-place density tests are summarized on
Table I. In general, the in-place density test results indicate that the fill soil has a dry density of at least
90 percent of the laboratory maximum dry density near to slightly above optimum moisture content at
the locations tested. The approximate locations of the in-place density tests are shown on the Interim
As-Graded Geologic Map (Figure 2). We performed the in-place density testing during the grading
operations for the subject site; therefore, the tests presented in Table I are not consecutive.
We tested samples of material used for fill to evaluate moisture-density relationships, optimum
moisture content and maximum dry density (ASTM D 1557). We performed direct shear tests (ASTM
D 3080) on samples used within fill slopes. We tested samples within the upper 3 feet of finish grade to
evaluate the expansion index (ASTM D 4829), water-soluble sulfate content (California Test No. 417),
and pH and resistivity (California Test No. 643). The results of the laboratory tests are summarized on
Tables II through VI.
Slopes
The project slopes consist of fill slopes constructed at inclinations of 2:1 (horizontal: vertical) or flatter
with maximum heights of approximately 5 and 15 feet, respectively. Slopes should be planted, drained,
and maintained to reduce erosion. Slope irrigation should be kept to a minimum to just support the
vegetative cover. Surface drainage should not be allowed to flow over the top of the slope.
SOILAND GEOLOGIC CONDITIONS
The soil and geologic conditions encountered during the grading operations are similar to those
described in the referenced geotechnical reports. The Santiago Formation (Ts) was exposed in pad
undercuts and cut areas within street right-of-ways. Compacted fill was placed in areas designated as
Qcf on Figure 2. In addition, compacted fill placed in undercut areas is designated as Quc. Table VII
presents a summary of As-Graded Building Pad Conditions for each pad.
Project No. 06403-52-32A - 3 - March 26, 2009
The Interim'As-Graded Geologic Map, Figure 2, depicts the general' geologic conditions observed. No
soil or geologic conditions were observed during grading that would preclude the continued
developmentof the property as planned.
- CONCLUSIONS AND RECOMMENDATIONS
1.0 General '
1.1 The grading has been performed in conformance with the recommendations of the previously
referenced project soils report by Geocon Incorporated and the geotechnilal requirements of I"
the grading plans. Soil and geologic conditions encountered during grading that differ from
those expected in the project soils report are not uncommon. Where such conditions required
a significant modification to the recommendations of the project soils report, they have been
described herein.
1.2 We did'not observe soil 'or geologic conditions during grading; that would preclude the
- ' continued development of the property as planne'd. Based on laboratory test results and field
observations, it is the opinion of Geocon Incorporated the fill observed and tested as part of
the grading for this project was generally compacted to a dry density of at least 90 percent of
rA the laboratory maximum dry density near to slightly above optimum moisture content.
1.3 The site is underlain by compacted fill and formational materials consisting of the Santiago
- Formation. We observed the placement of compacted fill during grading operations and
performed in-place density tests to evaluate the dry density and moisture content of the fill soil.
1.4 Laboratory testing of near-grade soil conditions indicates that the upper approximately 3 feet
of soil' underlying the pads possess a "very, low" to "low" expansion potential (expansion -
index of 50 or less). In addition, the samples indicate 'the soil possesses "severe" water-
soluble sulfate content.
1.5
•
The site is considered suitable for the use of conventional foundations with slabs-on-grade,
and/or post-tensioned foundation systems or on post-tensioned mat slabs. Foundation
categories for each of the subject lots are presented in Table VII;
1.6 Excavations within the fill and formational materials should generally be possible with
moderate to heavy effort using conventional heavy-duty equipment.
Project No. 06403-52-32A -4- March 26, 2009
2.0 Finish Grade Soil Conditions
2.1 Observations and laboratory test results indicate that the prevailing soil conditions within the
upper approximately 3 feet of-finish grade is considered to be "expansive" (expansion index
[El] of greater than 20) as defined by 2007 California Building Code (CBC) Section
1802.3.2. Table 2.1 presents soil classifications based on the expansion index. Results of the
El laboratory tests are presented in Table 1V. Based on our laboratory testing, the on-site soil
possesses a "very low" to "low" expansion potential (expansion index of 50 or less).
- TABLE 2.1 -
SOIL CLASSIFICATION BASED ON EXPANSION INDEX
Expansion Index (El) Soil Classificatiqn
0-20 Ver Low
21-50 - Low
51-90 Medium
91-130 High
Greater Than 130 Very High
2.2 We performed- laboratory tests on samples of the site materials to evaluate the percentage of
water-soluble sulfate content. Results from the laboratory water-soluble sulfate content tests
are presented in Table V and indicate that the on-site materials at the locations tested possess
"severe" sulfate exposure to concrete structures as defined by 2007 CBC Section 1904.3 and
ACI 318. Table 2.2 presents a summary of concrete requirements set forth by 2007 CBC
Section 1904.3 and ACI 318. The presence of water-soluble sulfates is not a visually
discernible characteristic; therefore, other soil samples from the site could yield different
concentrations. Additionally, over time landscaping activities (i.e., addition of fertilizers and
other soil nutrients) may affect the concentration. V
TABLE 2.2
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 V
-- -- --
Moderate 0.10-0.20 II 0.50 4000
Severe 0.20-2.00 V V 0.45 4500
Very Severe V > 2.00 V 0.45 4500
Project No. 06403-52-32A - V March
PI
2.3 We also subjected samples obtained for expansion index testing to pH and resistivity jesting.
These test results can be used to evaluate the potential for corrosivity and sulfate attack on
normal Portland Cement concrete and metal structures, pipes, and reinforcing steel. Test
results indicate the pH of subgrade soil is approximately 7.2. Resistivity test results indicate
soils possess resistivity values of approximately 500 ohm-cm. Results from the laboratory
pH and resistivity, testing tests are presented in Table VI.
2.4 Geocon Incorporated does not practice in the field, of corrosion engineering. Therefore, if
improvements that could be susceptible to corrosion are planned, further evaluation by a
corrosion engineer should be performed. -
3.0 Seismic Design Criteria
3.1 We used the computer program Seismic Hazard Curves and Uniform Hazard Response
Spectra, provided by the USGS to calculate the seismic design criteria. Table 3 summarizes
site-specific design criteria obtained from the 2007 California Building Code (CBC),
Chapter 16 Structural Design, Section 1613 Earthquake Loads. The short spectral response
has a period of 0.2 second. A Site Class C can be used for lots that possess a fill thickness of
less than 20 feet.
TABLE 3
2007 CBC SEISMIC DESIGN PARAMETERS
Parameter Value Reference
Site Class C D Table 1613.5.2 -
Fill Thickness T (Feet) T<20 T>20 --
Spectral Response - Class B (short), Ss 1.147g 1. 147g Figure 1613.5(3)
Spectral Response - Class B (1 sec), S 0.434g 0.434g Figure 1613.5(4)
- Site Coefficient, Fa' . 1.000 1.041 Table 1613.5.3(1)
Site Coefficient, F . 1.366 1.566 Table 1613.5.3(2)'
Maximum Considered Earthquake 1.147g 1.194g Section 1613.5.3 (Eqn 16-37) Spectral Response Acceleration (short), SMS
Maximum Considered Earthquake 0.592g 0.679g Section 1613.5.3 (Eqn 16-38) Spectral Response Acceleration —(1 'sec), Mi .
5% Damped Design .
Spectral Response Acceleration (short) SDS 0.765g 0.796g Section 1613.5.4 (Eqn 16-39)
5% Damped Design
Spectral Response Acceleration (1 sec), 5D1
0.395g , 0.453g Section 1613.5.4 (Eqn 16-40)
3.2 Conformance to the criteria in Table 3 for seismic design does not constitute any kind of
guarantee or assurance that significant structural damage or ground failure will not occur if a
Project No. 06403-52-32A - 6 - " March 26, 2009
maximum level earthquake occurs. The primary goal of seismic design is to protect life and
not to avoid all damage, since such design may be economically prohibitive.
4.0 Foundation and Concrete Stabs-On-Grade Recommendations
4.1 The foundation recommendations herein are for proposed one- to three-story residential
structures. The foundation recommendatins have been separated into three categories based
on either the maximum and differential fill thickness or Expansion Index. The foundation
category criteria are presented in Table 4.1.1.
TABLE 4.1.1
FOUNDATION CATEGORY CRITERIA
Foundation
Category
Maximum Fill
Thickness, T (feet)
Differential Fill
Thickness, D (feet)
Expansion Index
(El)
I T<20 - EI<50
II 20<T<50 10<13<20 50<Ek90
Ill T>50 D>20 90<EI<130
4.2 Final foundation ategories for the remaining lots will be provided after finish pad grades
have been achieved ándlaboratory testing of the subgrade soil has been completed.
4.3 Table 4.1.2 presents minimum foundation and interior concrete slab design criteria for
conventional foundation systems. -
TABLE 4.1.2
CONVENTIONAL FOUNDATION RECOMMENDATIONS BY CATEGORY
Foundation Minimum Footing Continuous Footing Interior Slab
Category Embedment Depth Reinforcement Reinforcement (inches)
I 12 Two No. 4 bars, 6 x 6 - 10/10 welded wire
one top and one bottom mesh at slab mid-point
II 18 Four No. 4 bars, No. 3 bars at 24 inches
two top and two bottom on center, both directions
III -24 Four No. 5 bars, No. 3 bars at 18 inches
two top and two bottom on center, both directions
4.4 The embedment depths presented in Table 4.1.2 should be measured from the lowest
adjacent pad grade for both interior and exterior footings. The conventional foundations
Project No. 06403-52-32A -,7 - March 26, 2009
should have a minimum width of 12 inches and 24 inches for continuous and isolated
footings, respectively. Figure 3 presents a typical wall/column footing dimension detail.
4.5 The concrete slab-on-grade should be a minimum of 4 inches thick for Foundation
Categories I and II and 5 inches thick for Foundation Category III.
4.6 Concrete slabs on grade should be underlain by 4 inches of clean sand (3 inches for a 5-inch-
thick slab) to reduce the potential for differential curing, slab curl, and cracking. Slabs that
may receive moisture-sensitive floor coverings or may be used to store moisture-sensitive
materials should be underlain by a vapor retarder placed near the middle of the sand bedding.
The vapor retarder used should be specified by the project architect or developer based on the
type of floor covering that will be installed. The vapor retarder design should be consistent
with the guidelines presented in Section 9.3 of the American Concrete Institute's (AC1) Guide
for Concrete Slabs that Receive Moisture-Sensitive Flooring Mtherials (ACI 302.2R-06).
4.7 As an alternative to the conventional foundation recommendations, consideration should be
given to the use of post-tensioned concrete slab and foundation systems for-the support of the
proposed structures. 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
(PTI), Third Edition, as required by the 2007 California Building Code (CBC
Section 1805.8). Although this procedure was developed for expansive soil conditions, we
understand it can also be used to reduce the potential for foundation distress due to
differential fill settlement. The post-tensioned design should incorporate the geotechnical
parameters presented on Table 4.1.3 for the particular Foundation Category designated. The
parameters presented in Table 4.1.3 are based on the guidelines presented in the PTI, Third
Edition design manual..
I
TABLE 4.1.3
POST-TENSIONED FOUNDATION SYSTEM DESIGN PARAMETERS
Post-Tensioning Institute (PTI),
Third Edition Design Parameters
Foundation Category
1 11
Thornthwaite Index -20 -20 -20
Equilibrium Suction 3.9 3.9 3.9
Edge Lift Moisture Variation Distance, em (feet) 5.3 5.1 4.9
Edge Lift, YM (inches) 0.61 1.10 1.58
Center Lift Moisture Variation Distance, em (feet) 9.0 9.0 9.0
Center Lift, YM (Inches) . 0.30 0.47 0.66
Project No. 06403-52-32A - 8 - March 26, 2009
4.8 The foundations for the post-tensioned slabs should be embedded in accordance with the
- recommendations of the structural engineer. If a post-tensioned mat foundation system is'
- planned, the slab should possess a thickened edge with a minimum width of 12 inches and
extend below the clean sand or crushed rock layer.
4.9 If the structural engineer proposes .a post-tensioned foundation design method other than
PT!, Third Edition:
The deflection criteria presented in Table 4.1.3 are still applicable.
Interior stiffener beams should be used for Foundation Categories II and III.
The width of the perimeter foundations should be at least 12 inches.
The perimeter footing embedment depths should be at least 12 inches, 18 inches and
24 inches for foundation categories I, II, and ffi, respectively. The embedment
depths should be measured from the lowest adjacent pad grade. -
4.10 Our experience indicates post-tensioned slabs are susceptible to excessive edge lift,
regardless of the underlying soil conditions. Plgcing reinforcing steel at the bottom of the
perimeter footings and the interior stiffener beams may mitigate this potential. Current PT!
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. .
4.11 During the construction of the post-tension foundation systein, 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.
4.12 Category. I, II, or ifi foundations 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 due to wind or seismic forces. The estimated
maximum total and differential settlement for the planned structures due to foundation loads
is 1 inch and '/2 inch, respectively.
4.13 - Isolated footings, if present, should have the minimum embedment depth and width
recommended for, conventional foundations foi a particular foundation category. The use of
isolated footings, which are located beyond the perimeter of the building 'and support
structural elements/ connected to the building, are 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.
Project No. 06403-52-32A . - 9 - ' ' March 26, 2009
4.14 For Foundation Category III, consideration should be given to using interior stiffening beams
and connecting isolated footings and/or increasing the slab thickness. In addition,
consideration should be given to connecting patio slabs, which exceed 5 feet in width, to the
building foundation to reduce the potential for future separation to occur.
4.15 Special subgrade presaturation is not deemed necessary prior to placing concrete; however,
the exposed foundation and slab subgrade soil should be moisture conditioned, as necessary,
to maintain a moist condition as would be expected in any such concrete placement.
4.16 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 fill slopes less than 20 feet high or cut slopes regardless of- height, 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.
When located next to a descending 3:1 (horizontal: vertical) fill slope or steeper, the
foundations should be extended to a depth where the minimum horizontal distance is
equal to H13 (where H equals the vertical distance from the top of the fill slope to the
base of the fill soil) with a minimum of 7 feet but need not exceed 40 feet. The
horizontal distance is measured from the outer, deepest edge of the footing to the
face of the slope. An acceptable alternative to deepening the footings would be 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. -
If swimming pools are planned, Geocon Incorporated should be contacted for a
review of specific site conditions.
Swimming pools located within .7 feet of the top of cut or- fill slopes are not
recommended. Where such a condition cannot be avoided, the portion of the
swimming pool wall within 7 feet of the slope face be designed assuming 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 recom-
mendations may be required and Geocon Incorporated should be contacted for a
review of specific site conditions.
- Although other improvements, which 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 which would permit some lateral soil
movement without causing extensive distress. Geocon Incorporated should be
consulted for specific recommendations:
Project No. 06403-52-32A _10 - March 26, 2009
4.17 The recommendations of this report are intended to reduce the potential for cracking of slabs
due to expansive soil (if present), differential settlement of existing soil or soil with varying
thicknesses. However, even with the incorporation of the recommendations presented herein,
foundations, stucco walls, and - slabs-on-grade placed on such conditions may still exhibit
some cracking due to soil movement and/or shrinkage. The occurrence of concrete shrinkage
cracks is independent of the supporting soil characteristics. Their occurrence may be reduced
and/or controlled by limiting the slump of the concrete,, proper concrete placement and
curing, and by the placement of crack control joints-at periodic intervals, in particular, where
re-entrant slab corners occur. -
4.18 Geocon Incorporated should be consulted to provide 'additional design parameters as
required by the structural, engineer.
-
5.0 Exterior Concrete Flatwork
- 5.1 Exterior concrete flatwork not subject to vehicular traffic should be constructed in
accordance with the recommendations herein. Slab panels should be a minimum of 4 inches
thick and when in excess of 8 feet square should be reinforced with 6x6-W2.9/W2.9
(6x6-6/6) welded wire mesh to reduce the potential for cracking. In addition, concrete
flatwork should be provided with crack control joints to reduce and/or control shrinkage
cracking. Crack control spacing should be determined by the project structural engineer
based upon the slab thickness and intended usage. Criteria of the American Concrete
Institute (ACT) should be taken into consideration when establishing crack control spacing
Subgradë soil for exterior slâb not subjected to vehicle loads should be compacted in
accordance with criteria presented in the grading section prior to concrete placement.
Subgrade soil should be properly compacted and the moisture content of subgrade soil
shäuld be verified prior to placing concrete.'
5.2 Even with the incorporation of the recommendations of this report, the exterior concrete
flatwork has a potential to experience some uplift due to expansive soil beneath grade. The
welded wire mesh should overlap continuously in flatwork to reduce the potential for vertical
offsets within flatwork. Additionally, flatwork should be structurally connected to the curbs,
-
where possible, to reduce the potential for offsets between the curbs and the flatwork.
5.3 Where exterior flatwork abuts the structure at entrant or exit points, the exterior slab should
be dowelled into the-structure's foundation sternwall. 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.
Project No. 06403-52-32A . - 11 - , March 26, 2009
6.0 Retaining Walls
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 2:1
(horizontal: vertical), an active soil pressure of 50 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 El of 50 or less. For those lots with
finish grade soils having an El greater than 50 and/or where backfill materials do not
conform to the criteria herein, Geocon Incorporated should be consulted for additional
recommendations. /
6.2 Unrestrained walls are those that are allowed to rotate more thai'iO.00lH (where H equals the
height of the retaining 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 active soil pressure. S
6.3 The structural engineer should determine the seismic design category for the project. If the
project possesses a seismic design category of D, B, or F, the proposed retaining walls
should be designed with seismic lateral pressure. The seismic load exerted on the wall should
be a triangular distribution with a pressure of 22H (where H is the height of the wall, in feet,
resulting in pounds per square foot [psf]) exerted at the top of the wall and zero at the base of
the wall. -
6.4 Although we evaluated the seismic loading on the wall for an active pressure case and the
walls will, be in an at-rest condition, some researchers have reported that this analysis
produces reasonable design earth pressures. Because seismic loads will be analyzed using
lower factors of safety than static earth pressures, we expect the design can be controlled by
static loads. S
6.5 Retaining walls should be provided with a drainage system adequate to prevent the buildup
of hydrostatic 'forces and waterproofed as required by the project architect. The soil
immediately adjacent to the backfilled retaining wall should be composed of free draining
material completely wrapped in Mirafi 140 (or equivalent) filter fabric for a lateral distance
of 1 foot for the bottom two-thirds of the height of the retaining wall. The upper one-third
should be backfilled with less permeable compacted fill to reduce water infiltration. The use
of drainage openings through the base of the wall' (weep holes) is not recommended where
the seepage could be a nuisance or otherwise adversely affect the proprty adjacent to the
base of the wall. A Typical Retaining Wall Drainage Detail is presented in Figure 4. The
recommendations herein assume a properly compacted granular (El of 50 or less)
Project No. 06403-52-32A - 12 - ' March 26, 2009
free-draining backfill material with no hydrostatic forces or imposed surcharge, load. If
conditions different than those described are expected, or if specific drainage details are
'desired, Geocon Incorporated should be contacted for additional recommendations.
6.6 In general, wall foundations having a minimum depth and width of 1 foot may be designed
for an allowable soil bearing pressure of 2,000 psf, provided the soil within 4 feet below the
base of the wall has an Expansion Index of 50 or less. 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 expected.
6.7 The recommendations presented herein 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.
7.0 Lateral Loads
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 or undisturbed formational materials. The allowable passive pressure
assumes a horizontal surface extending away from the base of the wall at last 5 feet or three
times the height of 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.
8.0 Site Drainage and Moisture Protection
8.1 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. 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.
Roofand pavement drainage should be directed into conduits that carry runoff away from the
proposed structure.
8.2 . 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. S '
Project No. 06403-52-32A - 13 - . March 26, 2009
8.3 If detention basins, bioswales,' retention basin, or water infiltration devices are being
considered, Geocon Incorporated should be retained toprovide recommendations pertaining
to the geotechnical aspects of possible impacts and design. Distress may be caused to
planned improvements and properties located hydrologically downstream. The distress
depends on the amount of water to be detained, its residence time, soil permeability, and
other factors. We have not performed a hydrogeology study at the site. Downstream
properties may be subjected to seeps, springs, slope instability, raised groundwater,
movement of foundatins and slabs, or other impacts as a result of water infiltration.
8.4 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 subdrains 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.
- LIMITATIONS
The conclusions and recommendations contained herein apply only to our work with respect to
grading, and represent conditions on the date of our interim observation on March 17, 2009. Any
subsequent grading should be done in conjunction with our observation and testing services. As used
herein, the term "observation" implies only that We observed the progress of the work with which we
agreed to be involved. Our services did not include the evaluation or identification of the potential
presence of hazardous or corrosive materials. Our conclusions and opinions as to whether the work
essentially complies with the job specifications are based on our observations, experience and test
results. Subsurface conditions, and the accuracy of tests used to measure such conditions, can vary
greatly at any time. We make no warranty, express or implied, except that our services were performed
in accordance with engineering principles generally accepted at this time and location.
We will accept no responsibility for any subsequent changes made to the site by others, by the
uncontrolled action of water, or by the failure of others to properly repair damages caused by the
uncontrolled action of water. The findings and recommendations 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.
The firm that performed the geotechnical investigation for the project should be retained to provide
testing and observation services during construction to provide continuity of geotechnical interpretation
and to check that the recommendations presented for geotechnical aspects of site development are
incorporated during site grading, construction of improvements, and excavation of foundations. If
another geotechnical firm is selected to perform the testing and observation services during
Project No. 06403-52-32A - 14 - March 26,2009
•
4
construction operations, that firm should prepare a letter indicating their intent to assume the 5 responsibilities of project geotechnical engineer of record. A copy of the letter should be provided to
the regulatory agency for their records. In addition, that firm should provide revised recommendations
5 concerning the geotechnical aspects of theproposed development, or a written acknowledgement of
S their concurrence with the recommendatirns presented in our report. They should also perform
S additional analyses deemed necessary to assume the role of Geotechnicál Engineer of Record. •
If you have any questions regarding this report, or if we may be of further service, please contact the
5 -
undersigned at your convenience.
Very truly yours,
GEOCON INCORPORATED -
Senior Staff Geologist CEG 1778 GE 2714
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ENGINEERING cc 06130109 rn GEOLOGW
WA
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S Project No. 06403-52-32A - 15- March 26, 2009
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SOURCE: 2008 THOMAS BROTHERS MAP
SAN DIEGO COUNTY, CALIFORNIA
REPRODUCED WITH PERMISSION GRANTED BY THOMAS BROTHERS MAPS. I
THIS MAP IS COPYRIGHT BY THOMAS BROS. MAPS, if IS UNLAWFUL TO COPY NO SCALE OR REPRODUCE ALL OR ANY PART THEREOF, WHETHER FOR PERSONAL USE OR
RESALE, WITHOUT PERMISSION.
GEOCON
INCORPORATED (4,00
GEOTEC-INICAL CONSULTANTS
6960 FLANDERS DRIVE - SAN DIEGO, CALIFORNIA 92121-2974
PHONE 858 558-6900 - FAX 858 558-6159
AS / DSKIGTYPD
VICINITY MAP
VILLAGES AT LA COSTA - THE GREENS
NEIGHBORHOOD 1.03, MODEL LOTS 1 THROUGH 3
CARLSBAD, CALIFORNIA
DATE 03-26- 2009 1 PROJECT NO. 06403 - 52 — 32A I FIG. 1
REENS - NEIGHBORHOOD 1.03
MODEL LOTS 1 THROUGH 3
CARLSBAD, CALIFORNIA S
7 -
A w I
or
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SCALE: I'= 30'
LEGEND
Qcf ........ COMPACTED FILL
QUID ........ COMPACTED FILL IN UNDERCUT AREA
Ts ........ SANTIAGO FORMATION (Dotted Where Eluded)
.........APPROX. LOCATION OF GEOLOGIC CONTACT
JG-48 ........APPROX. LOCATION OF IN-PLACE DENSITY TEST
FG ... Finish Grade ST ... Slope Test
.....APPROX. ELEVATION AT BASE OF FILL
GE000N
INCORPORATED
GEOTEO4NJCAL CONSULTANTS
6960 FLANDERS DRIVE. SAN DIEGO, CALIFORNIA 92121- 2974
PHONE 858558-6900- FAX 11,51155"159
PROJECT NO. 06403 -52 - 32A
INTERIM AS - GRADED GEOLOGIC MAP FIGURE 2
LADRILLONO
.'•
WALL FOOTING .
CONCRETE SLAB
.a_ •4 I '•4
SAND PAD GRADE
,,,
VISQUEEN
a. w 8w
tL \LL
Z-
-.
L FOOTING*
WIDTH
COLUMN FOOTING
. .
CONCRETE SLAB 4 --
A. $ • ',, 14e-
,a
a 1 •
SAND
VISQUEEN
' 4J
LL
' 5 •" -. .
FOOTING WIDTH
— —
/
*SEE REPORT FOR FOUNDATION WITDH AND DEPTH RECOMMENDATION , - No SCALE
WALL/ COLUMN FOOTING DIMENSION DETAIL
GEOCON
• .0. INCORPORATED . GEOTECHNICAL CONSULTANTS
6960 FLANDERS DRIVE - SAN DIEGO, CALIFORNIA 92121- 2974
PHONE 858 558-6900 - FAX 858 558-6159
AS/RA DSKIGTYPD •
.-
VILLAGES AT LA COSTA - THE GREENS'
NEIGHBORHOOD 1.03, MODEL LOTS 1 THROUGH 3
CARLSBAD, CALIFORNIA
DATE 03 - 26 - 2009 IPROJECT NO. 06403 -52 - 32A FIG. 3 —Ira—
GROUND SURFACE
ED\y4 TEMPORARY BACKCUT Pcm Q
MIRAPI 140 FILTER FABRIC
(OR EQUIVALENT)
OPEN GRADED
FOOTING
w
V MAX. AGGREGATE
4 DIA. PERFORATED SCHEDULE
40 PVC PIPE EXTENDED TO
1 APPROVED OUTLET
GROUND SURFACE
WATER PROOFING
PER ARCHITECT
DRAINAGE PANEL (MIRADRAIN 6000
OR EQUIVALENT)
3I4 CRUSHED ROCK
(1 CU.FTJFT.)
FILTER FABRIC ENVELOPE
v1-MIRAFI 140W OR EQUIVALENT
L—. 4 DIA. SCHEDULE 40 PERFORATED
PVC PIPE OR APPROVED TOTALDRAIN
EXTENDED TO APPROVED OUTLET
r
NOTE:
DRAIN SHOULD BE UNIFORMLY SLOPED TO GRAVITY OUTLET
OR TO A SUMP WHERE WATER CAN BE REMOVED BY PUMPING
NO SCALE
TYPICAL RETAINING WALL DRAIN DETAIL'
'GEOCON VILLAGESATIACOSTA - THEGREENS INCORPORATED NEIGHBORHOOD 1.03, MODEL LOTS 1 THROUGH 3 GEOTEcHNICAL CONSULTANTS - CARLSBAD, CALIFORNIA 6960 FLANDERS DRIVE - SAN DIEGO, CALIFORNIA 92121- 2974
PHONE 858 558-6900 - FAX 858 558-6159 -
A S! DSKIGTYPD JI DATE 03-26-2009 PROJECT NO. 06403-52- FIG. 4
W WIZUTEMPA-AL)TOCAD PLATE TPA 0TJI1RFTAE*IGWALL DRANAG/RET WALL DRAIN DRThJLSZDWG •
.5- 5
O
.. S
TABLE I
• SUMMARY OF FIELD DENSITY TEST RESULTS
Elev. Plus Field Field Field Req'd.
or 3/4" Dry Moist. Rel. Re!.
• Depth Curve Rock Dens. Cont. Comp. Comp.
Test No. Date Location (ft) No. (%) (pcf) (%)
SZ 8 12103/08 Lot 1;Wof Lot 1 295 3 0 110.8 12.6 92 90
•
SZ 9 12/03/08 Lot!; WofLot 1 294 3 0 110.2 12.9 92 90
'SZ 10 12/03/08 Lot 1;WofLoti 297 3 0 112.4 13.6 94 90
SZ 11 12/03/08 Lot 1;Wof Lot 1 293 3' 0 108.8 14.7 91 90
• 12 12/03/08 Lot 1 296 3 0 109.2 12.6 91 90
• SZ 13 12/03/08 Lot 1; W of Lot 1 299 3 0 1 09. 4 13.2 91 90
14 • 12/03/08 Lot 305 3 0 110.1 14.3 92 90
15 12/05/08 Lot 1 302 - 5 0 • 104.8 19.4 92 90
16 12/05/08 Lot ' 306 5 0 103.9 19.0 92 90 . 19 12/08/08 Lot ------------------------------------------------------------------------------------------------------------------------------------------------------------------------ - 305 3 0 110.6 12.8 92 90
20 12/08/08 Lot 308 3 0 108.2 13.6 90 90
SZ 33 01/16/09 Lot 1;S of Lot 1 • 293 3 0 108.6 13.7 90 90
ST 34 01/16/09 Lot 1;Sof Lot l 296 3 0 108.9 11.9 91 90
SZ 35 01/16/09 Lot 1;Sof Lot i 300 3 0 109.9 12.8 92 90
SZ 36 01/16/09 Lot 1;Sof Lot i
- -
. 304 3 0 109.5 12.6 91 90
SZ 37 0 1/20/09 0112.3115 90 90 . SZ 38 01/20/09 Lot 1;Sof Lot l 306 3 0 110.8 13.3 92 90
SZ 39 01/21/09 Lot 1; S ofLót 1 297 • 1 0 111.9 11.3 90 90
FG 46 03/17/09 Lot 308 : 3 0 110.3 13.9 92 90
FG 47 03/17/09 Lot 2 307 4 0 105.2 14.5 90 90
FG 48 03/17/09 Lot 306 3 0 108.1 13.1 90' 90 . . •
• •• •
S. S.
• . - •
. ,
• .
•
• .
• . . •
..' S .•
S . ,. . • ,.
• ••
.
,.
Project No. 06403-52-32A . . March 26, 2009
S. I
TABLE I
EXPLANATION OF CODED TERMS
TEST SUFFIX
A, B, C,.. : Retest of previous density test failure, following moisture conditioning and/or recompaction.
- STRIKE-OUT , / -
Fill in area of density test failure was removed and replaced 'wi6proper1y compacted fill soil.
- PREFIX CODE DESIGNATION FOR TEST NUMBERS
FG - FINISH GRADE' ' ST - SLOPE TEST
SZ - SLOPE ZONE '
CURVE NO.
'5 Corresponds to curve numbers listed in the summary of laboratory maximum dry density and optimum
i
•
moisture content test results table for selected fill soil samples encountered during testing and observation.
- ROCK CORRECTION
For density tests with rock percentage greater than zero, laboratory maximum dry density and optimum
moisture content were -adjusted for rock content. For tests with rock content equal to zero, laboratory
maximum dry density and optimum moisture content values are unadjusted. -
-TYPE OF TEST'
SC Sand Cone Test (ASTM D1556)
NU: Nuclear Density Test (ASTM D2922)
OT: Other . .
- ELEVATION/DEPTH
I •
Test elevations/depths have been rounded to the nearest whole foot.
- LOCATION DESCRIPTION
5 (IF): Indicates in-place tests. Where (IP) appears in the location description, the cornpactioi,procedures
-
were not observed by a representative of Geocon. Tests were taken at the surface or in test pits after
, placement of the fill. The results of these tests are indicative of the relative compaction at the location of
the test only and may not be extrapolated to adjacent areas. Geocon has-no opinion regarding the relative
5 - compaction of fill in adjacent areas.
• ' ,.
' ' . --.
,_ . ,. .. '
' , ' . -. .
'./'
I
,
.,-
-
. . .
. . --. .'
Project No. 06403-52-32A - ' ' , - ' March 26, 2009
...
. .
'
-.. -
'- '
TABLE II
SUMMARY OF LABORATORY MAXIMUM DRY DENSITY AND
OPTIMUM MOISTURE CONTENT TEST RESULTS
ASTMD1557
S.
Maximum Dry Optimum
Sample No. Description Density (pci) Moisture
- Content(%)
1 Olive brown, Silty SAND 124.2 11.0
2 Brown, Clayey SAND 127.4 10.2
3 Dark brown, Clayey, fine to medium SAND 120.1 11.9
4 . Light yellowish brown, Silty SAND 116.5 13.3
5 Light brown to reddish brown , Silty to Clayey SAND 113.4 15.0
6 Yellowish brown, Clayey, fine to medium SAND 122:5 11.3
TABLE III
SUMMARY OF LABORATORY DIRECT SHEAR TEST RESULTS
ASTM D 3080
Sample No: Dry Density
(pci)
Moisture Content (°) - Unit Cohesion Angle of
Shear Resistance
(degrees)- Initial I Final
1 110.1 12.5 23.4 270 32
2 114.2 10.4 18.4 225 33 -
Samples were remolded to approximately 90, percent of laboratoryy, maximum dry density at near optimum moisture
content.
- TABLE IV
SUMMARY OF LABORATORY EXPANSION INDEX TEST RESULTS
ASTMD4829
Sample I Moisture Content (%) I Dry Density I Exp ansion Expansion Lot No. No. (pci) 'Index I Classification I I Before Test I I After Test
l through 3 El-A 10.9 21.5 111.2 28 Low
I
TABLE
SUMMARY OF WATER SOLUBLE SULFATE LABORATORY TEST RESULTS
CALIFORNIA TEST NO. 417
Sample No. - Water Soluble Sulfate (%) Sulfate Exposure
- El-A . 0.320 - Severe
Project No. 06403-52-32A March 26, 2009
(
TABLE VII . SUMMARY OFAS-GRADED RESIDENTIAL BUILDING PAD CONDITIONS
THE GREENS, NEIGHBORHOOD 1.03; LOTS 1 THROUGH 3
.. • Approximate Approximate Recommended
Lot No. Pad Condition Maximum Maximum Depth . Expansion Foundation Depth of Fill of Fill Differential Index Category (feet) (feet)
1 Fill 14 7 28 I
2 Undercut due to 15 12 28 II cut/fill transition
Undercut due to 8 . 5 28 I cut/fill transition -
• TABLE VI
SUMMARY OF LABORATORY POTENTIAL OF HYDROGEN (pH),
RESISTIVITY, CALIFORNIA TEST NO. 643
.- . Sample'No. pH Resistivity (ohm/cm)
El-A 7.2 500
- TABLE VIII
. SUMMARY OF CBC SOIL PROFILE TYPE
'.- - -
. THE GREENS NEIGHBORHOOD 1.03; LOTS 1 THROUGH 3
- Lot No. 2007 CBC Soil Profile Type
l through 3 C