HomeMy WebLinkAboutCT 04-03; LA COSTA RIDGE NEIGHBORHOODS 2.3 & 2.4; UPDATE GEOTECHNICAL REPORT; 2006-01-26UPDATE
GEOTECHNICAL REPORT
VILLAGES OF LA COSTA -THE. RIDGE
NEIGHBORHOODS .23 AND 2.4.
(NORTH)
LOTS 49 THROUGH 103
CARLSBAD, CALIFORNIA
PREPARED FOR
SHEA HOMES
SAN DIEGO, CALIFORNIA
JANUARY 26, 2006
PROJECT NO. 07290-52-05
TABLE OF CONTENTS
PURPOSEANDSCOPE ..................................................................................................1
PREVIOUS SITE DEVELOPMENT .................................................................................................1
3 SITE AND PROJECT DESCRIPTION 1
4.. SOIL AND GEOLOGIC CONDITIONS 1
4.1 Compacted Fill (Qcf) .......................................
.
......................................................................... 1
4.2 San Marcos Gabbro (Kg [Sm.]) ................................................................................................1
4.3. Escohdido Creek Granodiorite (Kg [e]) .................................................................................
44 . Bonsall Tonalite (Kg[b,])...........................................................................................................i
4.5 . Santiago Peak Volcanics (Jsp) ... ..............................................................................................
5. GROUNDWATER ............................................................................................................................1
.6. GEOLOGIC-HAZARDS ...................................................................................................................1
6.1 Faulting and Seismicity 1
6.2 Liquefaction 1
7 CONCLUSIONS AND RECOMMENDATIONS
7.1 General.....................................................................................................................................
7.2 Seismic Design .........................................................................................................................1
7.3 Finish Grade Soil Conditions ..................................................................................................
7.4 Future Grading..........................................................................................................................
7.5 Fundations ............................................................................................................................ 1
.7.6 . Retaining Walls .......................................................................................................................1
7.7 Lateral Loads............................................................................................................................
7.8 Slope Maintenance ................................................................................................................1
7.9 Site Drainage ..........................................................................................................................
LIMITATIONS AND UNIFORMITY OF CONDITIONS. . . . . ., .. . . .
MAPS AND ILLUSTRATIONS . . . .
Figure 1, Vicinity Map ..
Figure 2 Retaining Wall Drain Detail
TABLES . . . . . . .
Table I, Summary of As-Graded Building Pad Conditions and Foundation Category.
Table II, Summary of Laboratory WaterSoluble Sulfate Test Results .
UPDATE GEOTECHNICAL REPORT
1. PURPOSE AND SCOPE
This report presents the results of the update geotecimical study for the proposed residential
development of Neighborhoods 2.3 and 2.4 (North) Lots 49 through 103 and associated
improvements located in the Villages of La Costa - The Ridge development. The site is generally
situated east of El Fuerte Street and north of Corintia Street in Carlsbad, California (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 Geotechnical Investigation, Villages of La Costa - The Ridge, Carlsbad, California,
prepared by Geocon Incorporated, dated August 27, 2001 (Project No. 06105-12-05).
Final Report of Testing and Observation Services Performed During Site Grading, Villages
of La Costa - The Ridge, Neighborhoods 2.3 and 2.4, Carlsbad, California, prepared by
Geocon Incorporated; dated September 16, 2005. (Project No. 07290-52-01).
Grading and Erosion Control Plans for: La Costa Ridge Neighborhood 2.3 and 2.4, prepared
by Hunsaker and Associates, City of Carlsbad approval dated August 23 2005.
2. PREVIOUS SITE DEVELOPMENT
Neighborhoods 2.3 and 2.4 (North), Lots 49 through 103 were graded to finish pad configuration
during mass grading operations for the Villages of La Costa —The Ridge 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 final report of grading. Mass grading for the subject
area has been completed and' consisted of developing 55 single-family residential, lots and associated
streets. Fill slopes were created with design inclinations of 2:1 (horizontal: vertical) or flatter, with a
maximum height of approximately 45 feet. The maximum thickness of the fill soil is approximately
42 feet. An "As-Graded" Geologic Map has been provided in the above-referenced final report and
depicts the existing geologic conditions and topography.
3. SITE AND PROJECT DESCRIPTION
The development of the subject neighborhoods within The Ridge consists of 55 single-family
residential homes and associated improvements: Compacted fill soil is exposed at grade and is
underlain by volcanic and granitic rock consisting of the Santiago. Peak Volcanics, Bonsall Tonalite,
San Marcos Gabbro, and Escondido Creek Granodiorite. A summary of the as-graded pad conditions
for each lot is provided on Table I. In general, the on-site fill materials generally vary between
Project No. 07290-52-05 ' - 1- January 26. 2006
angular gravels and boulders produced by onsite blasting of hard rock to silty, fine to coarse sands
and sandy to clayey gravels derived from the surficial soils and weathered formational materials.
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 site is underlain by compacted fill and geologic formations of the Jurassic-age Santiago Peak
Volcanics and Cretaceous-age Bonsall Tonalite, San Marcos Gabbro, and Escondido Creek
Granodiorite. The fill soil within 3 feet of grade consists of silty sand and gravel and possess a "very
low" expansion potential. The soil type and geologic units are discussed below.
4.1 Compacted Fill (Qcf)
In general, structural fill placed and compacted at the site consisted of material which can be
classified into three zones:
Zone A Material placed within 3 feet from pad grade, 6 feet from parkway grade, and within
roadways to at least 1 foot below the deepest utility consisted of "soil" fill with an
approximate maximum particle dimension of 6 inches.
Zone B Material placed within 10 feet from pad grade and below Zone A consisted of "soil
rock" fill with a maximum particle dimension of 12 inches. In addition, material
placed on the outer 6 feet of fill slopes and 2 feet below Zone A for fills in roadways
and parkways consisted of "soil rock" fill with a maximum particle dimension of
12 inches.
Zone C Material placed below Zone B consisted of "soil rock" fill and "rock" fill with a
maximum particle dimension of 48 inches. It should also be noted that larger rocks
with a maximum dimension of approximately 8 feet were buried individually during
"rock" fill grading operations.
The maximum fill thickness is approximately 42 feet. Fill soil was placed in conjunction with the
observation and testing services of Geocon Incorporated which have been summarized in the
above-referenced final report of grading. The compacted fill soil is considered suitable to provide
adequate support for the proposed development.
Project No. 07290-52-05 - 2 - January 26. 2006
4.2 San Marcos Gabbro (Kg [Sm])
, The Cretaceous-aged San Marcos Gabbro was encountered as isolated bodies within the project. This
unit is typically characterized as moderately weathered, fractured, fine- to medium-grained, dark gray
gabbro.
4.3 Escondido Creek Granodiorite (Kg [e])
In published literature, this unit is described as a "leucogranodiorite" because of the overall light
color, but averages of composition are typically granodiorite. This rock type was encountered at most
areas within the site, and generally consists of slightly to moderately weathered, light brown to olive,
medium- to coarse-grained granodiorite.
4.4 Bonsall Tonalite (Kg [b])
The Bonsall Tonálite was mapped as resistant, quartz-rich diorite bodies that were commonly
associated with the contact between Escondido Creek Granodiorite and the San Marcos Gabbro or
Santiago Peaks Volcanics. This rock type was'encountered at most areas of the site, and formed
resistant ridges and outcrops prior to grading. The Bonsall Tonalite is fine- to medium-grained,
slightly to moderately weathered, and contained gabbro or volcanic inclusions. Fine-grained and
unweathered portions of the Bonsall Tonalite required heavy ripping effort, blasting or breaker
hammers to excavate.
4.5 Santiago Peak Volcanics (Jsp)
The Jurassic-aged Santiago Peak Volcanics underlies the south and east margins of the site. it also
occurs as isolated masses within the granitic bedrock throughout the site. These rocks were deposited
as an alternating succession of volcanic flows, tuffs, and breccias and typically have an andesite or
dacite composition. Subsequently, this sequence Of rocks was folded, faulted, and weakly
metamorphosed. As encountered during grading, this unit is highly fractured. Closely spaced parallel
fractures and joints form "sheeted" zones containing colorful alteration and/or oxidation minerals
such.as limonite and hematite. Even though the majority of the Santiago Peak Volcanics appears to
be highly fractured and altered, the "sheeted" zones typically have steeply dipping, tight clay-filled
fractures.
5. GROUNDWATER
Groundwater was not encountered during grading operations and is not anticipated to adversely
impact the development of the property. Due to the fractured nature of the formational materials,
some areas of seepage were encountered and contained during remedial grading by subdrains. 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
Project No. 07290-52-05 - 3 - January 26, 2006
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 August 27, 2001, and our experience with the soil and geologic conditions in the general
area indicate that no known active, potentially active, or inactive faults are located at the site.
The nearest known "active" faults are the Rose Canyon Fault and the Newport-Inglewood (offshore)
located approximately 8 and 12 miles, respectively, to the west and the Elsinore Fault Zone, which
lies approximately 23 miles to the northeast. Portions of the Rose Canyon Fault have been included in
an Alquist-Priolo Earthquake Fault Zone. A Maximum Credible seismic event of Magnitude 7.2 is
'postulated for the Rose Canyon Fault with an estimated Maximum Credible peak site acceleration of
0.35 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
California and northern Baja California region. Table 6.1 lists the fault zones that present the greatest
seismic impact to the site.
TABLE 6.1
FAULT SYSTEMS WITHIN THE SOUTHERN CALIFORNIA AND
NORTHERN BAJA CALIFORNIA REGION
Fault Name Distance from Site
' (miles)
Maximum
Credible Earthquake
Maximum Credible
Site Acceleration (g)
Rose Canyon 8 ' 7.2 0.35
Newport—Inglewood (Offshore) 12 7.1 0.24
Coronado Banks Fault Zone 23 , 7.6 0.16
Elsinore—J,ulian ' 23 7.1 ' 0.12
Elsinore—Temecula 23 6.8 0.10
Elsinore—Glen Ivy 38 6.8 0.05
Earthquake Valley 38 6.5 0.04
San Joaquin Hills , 42 ' 6.6 0.04
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
Project No. 07290-52-05 ' -4 - ' January 26,
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 and absence of a permanent groundwater table, the potential for
liquefaction occurring at the site is considered to be very low.
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 consideredsuitable 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 underlies the proposed buildings. For seismic design, the site is characterized by soil
profile types Sc and 5D• Table 7.2.1 summarizes site design criteria. The values listed in
Table 7.2.1 are for the Rose Canyon Fault, which is identified as a Type B fault. The Rose
Canyon Fault is located approximately 8 miles west of the site. Table 7.2.2 presents a
summary of soil profile type for each building and the corresponding values from
Table 7.2.1 should be used for seismic design. ,
Project No. 07290-52-05 . - 5 - January 26, 2006
TABLE 7.2.1
SITE SEISMIC DESIGN CRITERIA
Parameter
Soil Profile Type
UBC Reference
Sc SD
Seismic Zone Factor 0.40 0.40 Table 16-I
Soil Profile Sc S0 Table 16-f
Seismic Coefficient, C 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
7.2.2 Based on review of the as-graded conditions presented-in the referenced as-graded report,
as well as the seismic setting, the lots are assigned the seismic design parameters as
indicated below in 7.2.2.
TABLE 7.2.2
SUMMARY OF SOIL PROFILE TYPE
• Lot Nos. UBC
Classification
52, 56 through 60, 62, 63, 70 through 76, 78 through 86, 90 through 95 and 103 Sc
49 through 5 1, 53 through 55, 61, 64 through 69, 77, 87 through 89,
and 96 through 102 0
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 "very low"
(Expansion Index of 20 or less) as defined by Uniform Building Code (UBC) Table 18-1-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 3 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
Project No. 07290-52-05 - 6 - January 26, 2006
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" sulfate exposure ratings as defined by UBC Table 19-A-4. The results of the
water-soluble sulfate tests are summarized on Table H.
7.3.4 . Geocon Incorporated does not practice in the field of corrosion engineering. Therefore, if
improvements that could be susceptible to corrosion areplanned, 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 niaximurn 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 We understand that a post-tensioned foundation system will be used. 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 soil of a particular
building pad. Finish grade Expansion Index test results are presented on Table I, attached.
The category criteria are summarized herein.
Category 1: 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 less than or equal to 130.
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. .
Project No. 07290-52-05 - 7 - January 26, 2006
All interior living area concrete slabs should be at least 5 inches thick for all
categories. This applies to both building and garage slabs-on-grade.
All interior concrete slabs should be underlain by at least 3 inches of clean sand or
crushed rock.
All slabs expected to receive moisture sensitive floor coverings or used to store
moisture sensitive materials should be underlain by a vapor inhibitor covered with at
least 2 inches of the clean sand recommended in No. 4 above.
7.5.2 The post-tensioned systems should be designed by a structural engineer experienced in
post-tensioned slab design and design criteria of the Post-T-ensioning Institute (TJBC
Section 1816). Although this procedure was developed for expansive soils, it can also be
used to reduce the potential for foundation distress due to differential fill settlement. The
post-tensioned design should incorporate the geotechnical parameters presented in Table
7.5 entitled Post-Tensioned Foundation Systems Design Parameters for the particular
foundation category designated.
TABLE 75
POST-TENSIONED FOUNDATION SYSTEM DESIGN PARAMETERS
Post-Tensioning Institute (PTI)
Design Parameters
Foundation Category
Thornthwaite Index -20 -20 -20 -
Clay Type - Montmorillonite Yes Yes Yes
Clay Portion (Maximum) 30% 50% 70%
Depth to Constant Soil Suction 7.0 ft. 7.0 ft. 7.0 ft.
Soil Suction 3.6 ft. 3.6 ft. 3.6 ft.
Moisture Velocity 0.7 in/mo. 0.7 in/mo. 0.7 in/mo.
Edge Lift Moisture Variation Distance 2.6 ft. 2.6 ft. 2.6 ft.
Edge Lift 0.41 in. 0.78 in. 1.15 in.
Center Lift Moisture Variation Distance 5.3 ft. 5.3 ft. 5.3 ft.
Center Lift 2.12 in. 3.21 in. 4.74 In.
7.5.3 UBC Chapter 18, Div. Ill, §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 III.
Project No. 07290-52-05 - 8 - January 26, 2006
The depth of the perimeter foundation should be at least 12 inches for Foundation
Category I, 18 inches for Foundation Category 11, 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-tensioned 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 systemto 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, H, or UI may be designed for an allowable soilbearing
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 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.
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.
Project No. 07290-52-05 - 9 - January 26, 2006
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 HJ3 (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
Incorpórateçl 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 wiie 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.
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.
Project No. 07290-52-05 - 10 - • January 26, 2006
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-ongrade placed on such conditions
may still exhibit some cracking due to soil movement and/or shrinkage. The occurrence of
concrete shrinkage cracks is independent of the supporting soil characteristics. Their
occurrence may be reduced and/or controlled by limiting the slump of the concrete, proper
concrete placement and curing, and by the placement of crack-control joints at periodic
intervals, particularly where re-entrant slab 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 50. For those lots with
finish grade soils having an Expansion. Index greater than 50 and/or where backfill
materials do not conform to the above criteria, Geocon Incorporated should be consulted
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 71-1 psf
should be added to the above active soil pressure. For retaining walls subjected to vehicular
loads within a horizontal distance equal to two-thirds of the wall height, a surcharge
equivalent to 2 feet soil should be added.
7.6.3 All retaining walls should be provided with a drainage system adequate to prevent the
buildup of hydrostatic forces and should be waterproofed as required by the project
architect. The use of drainage openings through the base of the wall (weep holes, etc.) is
not recommended where the seepage could be a nuisance or otherwise adversely impact the
property adjacent to the base of the wall. 'A typical retaining wall drainage system is
Project No. 07290-52-05 - 11- January 26, 2006
presented as Figure 2. The above recommendations assume a properly compacted granular
(Expansion Index less. than 50) backfillmaterial with no hydrostatic forces or imposed
surchargeload. 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 90 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
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 appliáable 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 are planned, such as crib-type walls, Geocon
Incorporated should be consulted for additional recommendations.
7.8 Slope Maintenance
7.8.1 Slopes that are steeper than 3:1 (horizontal: vertical) may, under conditions that are both
difficult to prevent and predict, be susceptible to near-surface (surficial) slope instability.
The instability is typically limited to the outer three feet of a portion of the slope and
usually does not directly impact the improvements on the pad areas 'above or below the
slope. The occurrence of surficial instability is more prevalent on fill slopes and is
generally preceded by a period of heavy rainfall, excessive irrigation or the migration of
subsurface seepage. The disturbance and/or loosening of the surficial soils, as might result
Project No. 07290-52-05 - 12 - January 26, 2006
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 projects 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. 07290-52-05 - 13 - January 26, 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, whethef 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. 07290-52-05 January 26, 2006
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SOURCE 2006 THOMAS BROTHERS MAP
SAN DIEGO COUNTY, CALIFORNIA
REPRODUCED WITH .PERMISSION GRANTED BY THOMAS BROTHERS MAPS.
THIS MAP IS COPYRIGHTED BY THOMAS BROS. MAPS. IT IS UNLAWFUL TO COPY
OR REPRODUCE ALL OR ANY PART THEREOF. WHETHER FOR PERSONAL USE OR RESALE, WITHOUT PERMISSION
.GE000N 0 INCORPORATED
GEOTECHNICAL, CONSULTANTS
6960 FLANDERS DRIVE - SAN DIEGO, CALIFORNIA 92121-2974
PHONE 858 558-6900 - FAX 858 558-6159
AS/RSS . DSK/D000D
7290-52-05_it? VICMAP
It
NO SCALE
VICINITY MAP
VILLAGES OF LA COSTA - THE RIDGE
NEIGHBORHOOD 2.3 AND 2.4. (NORTH)
CARLSBAD, CALIFORNIA
DATE 01-. 26- 2006 1 PROJECT NO. 07290 -52 - 05 1 FIG. '1
GROUND SURFACE
2.0
CONCRETE LINE
DRAINAGE DITCH
4fl
PROPOSED - PROPERLY /
RETAINING WALL - COMPACTED / BACKFILL /
-I------ /
/ MIRAFI 140 FILTER
•. FABRIC OR EQUIVALENT
2/3 H CLEAN, FREE DRAINING
3/4" CRUSHED GRAVEL
12' TMAX. •
G ROUND SURFACE
FOOTING 4 01k PERPORATED PVC
PIPE MIN. 1/2% FALL TO-
APPROVED OUTLET
NOTES:
1......PREFABRICATED DRAINAGE PANELS, SUCH AS MIRADRAIN 7000 OR EQUIVALENT,
MAYBE USED IN LIEU OF PLACING GRAVEL TO HEIGHT OF 2/3 THE TOTAL WALL HEIGHT
2......DRAIN SHOULD BE UNIFORMLY SLOPED AND MUST LEAD TO A POSITIVE GRAVITY OUTLET
3......TEMPORARY EXCAVATION SLOPES SHOULD BE CONSTRUCTED AND/OR SHORED IN
ACCORDANCE WITH CAL-OSHA REGULATIONS
NO SCALE
RETAINING WALL DRAIN DETAIL
.GEOCON . VILLAGES OF LA COSTA - THE RIDGE
INCORPORATED NEIGHBORHOOD 2.5 GEOTECI-INICAL CONSULTANTS
6960 FLANDERS DRIVE - SAN DIEGO, CALIFORNIA 92121- 2974 CARLSBAD, CALIFORNIA
PHONE 858 558-6900 - FAX 858 558-6159
AS/ RSS I DSKJGTYPD DATE 01 -26 - 2006 PROJECT NO. 07290 - 52-07 1 FIG. 2
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TABLE I
SUMMARY OF AS-GRADED. BUILDING PAD CONDITIONS
AND FOUNDATION CATEGORY
THE RIDGE, NEIGHBORHOODS 2.3 AND 2.4 (NORTH),
LOT NOS. 49 THROUGH 103
Approximate Approximate Depth of Expansion Foundation
Lot No. Pad Condition Maximum Differential Index Category Depth of Fill Fill
49 Fill 31 26 0 III
50 Undercut due to cut/fill 23 20 0 III
transition
TABLE I (Continued)
SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS
AND FOUNDATION CATEGORY
THE RIDGE, NEIGHBORHOODS 2.3 AND 2.4 (NORTH),
LOT NOS. 49 THROUGH 103
Approximate Approximate
TABLE I (Continued)
SUMMARY OF AS-GRADED BUILDING PAD CONDITIONS
AND FOUNDATION CATEGORY
THE RIDGE, NEIGHBORHOODS 2.3 AND 2.4 (NORTH),
LOT NOS. 49 THROUGH 103
Lot No. Pad Condition
Approximate
Maximum
Depth of Fill
Approximate
Depth of
Differential
Fill
Expansion
Index
Foundation Category
95 Fill 18 10 0 II
96 Fill 27 21 2 III
97 Fill .31 8 2 II
98 Fill 36 10 2 II
99 Fill 34 10 2 II
100 Fill 34 17 0 . II
101 . Fill 31 20 0 III
102 Fill 24 21 0 Ill
103 . Fill 15 11 0 II
TABLE II
SUMMARY OF LABORATORY WATER-SOLUBLE SULFATE TEST RESULTS
CALIFORNIA TEST 417
Sample No. . Water-Soluble Sulfate (%) Sulfate Exposure
El 19 0.006 Negligible
El 20 0.002 . Negligible
E121 0.005 Negligible
El 22 0.010 Negligible
El 23 0.005 . Negligible
El 24 0.006 Negligible
El 25 0.006 Negligible
El 26 . 0.014 Negligible
El 27 . 0.015 Negligible
El 28 0.004 Negligible
El 29 0.005 Negligible
Project No. 07290-52-05 January 26, 2006
Project No. 07290-52-05
January. 26, 2006
SheaHbmes
9990 Mesa Rim Road
San Diego, California 92121
Attention: Mr. Greg Ponce
Subject: VILLAGES OF LA COSTA - THE RIDGE
NEIGHBORHOODS 2.3 AND 2.4 (NORTH), LOTS 49 THROUGH 103
CARLSBAD, CALIFORNIA
UPDATE GEOTECHNICAL REPORT
Gentlemen:
In accordance with your authorization of our Proposal No. LG-05430 dated October 11, 2005, we
have prepared this update geotechnical report for .the subject .project. The accompanying report
presents the results of our study and contains concluions"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
. %ON4L
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CEG 1524 CEG 1778 EWNEERWa
ASJH:SR:anh O:OFESS,
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CALIf
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(6/del) Addressee
(2) Morrow Development co No.63291
Attention:' Mr.'im O'Grady Exp. 6/30/06 rn cr-
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