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THE GARRETT GROUP March 28, 2001
TRs 23066-1, -2 & -3/Temecula Area J.N. 140-01
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TABLE OF CONTENTS
Section Pale
INTRODUCTION.................................................. 1
Location and Site Description ...................................... I
Proposed Development/Grading..................................... 2
Background Information...........................................2
Purpose and Scope of Services ...................................... 2
INVESTIGATION AND LABORATORY TESTING ...................... 3
Field Exploration................................................3
Laboratory Testing...............................................4
FINDINGS........................................................ 4
Regional Geologic Setting ......................................... 4
Local Geology and Soil Conditions .................................. 5
Earth Materials ................................................ 5
Groundwater....................................................6
Faulting........................................................6
CONCLUSIONS AND RECOMMENDATIONS .........................
7
General........................................................7
Earthwork......................................................7
General Earthwork and Grading Specifications .......................
7
Clearing and Grubbing ..........................................
7
Excavation Characteristics .......................................
8
Groundwater..................................................8
Ground Preparation - Fill Areas ...................................
9
Canyon Subdrains.............................................
9
Fill Placement...............................................10
Benching...................................................10
Import Soils for Grading .......................................
10
Processing of Cut Areas ........................................
10
Cut/Fill Transition Lots ........................................
11
Shallow Fill -to -Deep -Fill Lots ...................................
11
Shrinkage, Bulking and Subsidence ...............................
12
CutSlopes..................................................12
FillSlopes..................................................13
Fill -Above -Cut and Cut -to -Fill Transition Slopes ....................
13
Geotechnical Observations .....................................
14
Post -Grading Considerations ......................................
14
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THE GARRETT GROUP
TRs 23066-1, -2 &-3/Temecula Area
TABLE OF CONTENTS (Continued)
March 28, 2001
J.N. 140-01
Page ii
Deep -Fill -Settlement Monitoring ................................. 14
Slope Landscaping and Maintenance .............................. 15
Natural Slopes ............................................... 17
Expansive Soil Considerations .................................. 24
Post-Tensioning..............................................28
Retaining Walls ................................................ 29
Footing Embedments.......................................... 29
Active and At -Rest Earth Pressures ............................... 30
Drainage....................................................30
iTemporary Excavations........................................31
WallBackfill................................................31
L Construction on Level Ground ................................... 32
Construction Joints ............................................ 32
Preliminary Structural -Pavement Design ............................. 33
Concrete Flatwork.............................................. 34
Thickness and Joint Spacing .................................... 34
Subgrade Preparation .......................................... 34
Planters.......................................................34
Soluble -Sulfate Analyses ....................................... 35
GRADING -PLAN REVIEW AND CONSTRUCTION SERVICES .......... 35
INVESTIGATION LIMITATIONS ................................... 36
Utility Trenches ..............................................
17
Site Drainage ................................................
18
Seismic -Design Considerations ....................................
18
Ground Motions ..............................................
18
Secondary Effects of Seismic Activity ............................
20
Soil Corrosivity................................................21
Tentative Foundation -Design Recommendations ......................
21
General.....................................................
21
Allowable -Bearing Values ......................................
22
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Settlement ..................................................
22
Lateral Resistance .............................................
22
Footing Setbacks From Descending Slopes ........... . ....
. ........ 23
Building Clearances From Ascending Slopes .......................
23
Footing Observations ..........................................
23
Expansive Soil Considerations .................................. 24
Post-Tensioning..............................................28
Retaining Walls ................................................ 29
Footing Embedments.......................................... 29
Active and At -Rest Earth Pressures ............................... 30
Drainage....................................................30
iTemporary Excavations........................................31
WallBackfill................................................31
L Construction on Level Ground ................................... 32
Construction Joints ............................................ 32
Preliminary Structural -Pavement Design ............................. 33
Concrete Flatwork.............................................. 34
Thickness and Joint Spacing .................................... 34
Subgrade Preparation .......................................... 34
Planters.......................................................34
Soluble -Sulfate Analyses ....................................... 35
GRADING -PLAN REVIEW AND CONSTRUCTION SERVICES .......... 35
INVESTIGATION LIMITATIONS ................................... 36
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ITHE
GARRETT GROUP
TRs 23066-1, -2 &-3/Temecula Area
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TABLE OF CONTENTS (Continued)
Figure 1 - Site Location Map
References
Plate 1 - Geotechnical Map (in pocket)
Appendices
Appendix A - Logs of Test Pits
Appendix B - Laboratory Test Criteria/Laboratory Test Data
Appendix C - Seismic
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March 28, 2001
J.N. 140-01
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UPDATED GEOTECHNICAL INVESTIGATION,
TRACTS 23066-1,23066-2 AND 23066-3, REDHAWK DEVELOPMENT
TEMECULA AREA, RIVERSIDE COUNTY, CALIFORNIA
INTRODUCTION
This report presents the results of Petra Geotechnical, Inc.'s (Petra's) updated
geotechnical investigation of Tracts 23066-1, 23066-2 and 23066-3, Redhawk
development in the Temecula area of Riverside County, California. The purposes of
this investigation were to determine the nature of surface- and subsurface -soil
conditions and to evaluate their in-place characteristics; provide geotechnical
recommendations with respect to site grading; and for design and construction of
fbuilding foundations. This investigation also included a review of our previous reports
published and unpublished literature (see References), as well as geotechnical maps
pertaining to active and potentially active faults that lie in proximity to the site and
r which may have an impact on the proposed construction.
Location and Site Description
The irregularly shaped subject site, in which portions are currently occupied by
Fairways 5 through 9 of the Redhawk Country Club, is currently vacant and is located
in the Temecula area of Riverside County, California.
�. Topography is characterized by numerous ridges and low rounded hills with
intervening valleys, canyons and gullies. Natural slopes vary from near horizontal to
near vertical at the contact with adjoining lower canyons and valleys. Graded
manmade slopes off of the existing golf -course are generally at a 2:1 (horizontal/
vertical [h:v]) orientation. Maximum topographic relief throughout the subject site is
approximately 145 feet with existing surface elevations ranging from 1,110 to 1,254
feet above sea -level. Drainage is multi -directional and occurs both as sheet flow and
concentrated runoff in the drainage swales. Vegetation consist of desert type scrub
brush, trees, weeds and grasses. There were no evidence of springs or seeps observed
within the subject site during the course of this supplemental investigation. Due to
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ITHE GARRETT GROUP March 28, 2001
TRs 23066-1, -2 &-3/Temecula Area J.N. 140-01
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recent rains, standing water was observed within the man-made retention basins
created with the associated golf -course. No underground structures are known to be
present within the subject site.
The site is bordered on the north by an existing elementary school and single-family
residences, to the south and east by Redhawk Parkway and to the west by Fairway 9.
The general location of the site is shown on Figure 1.
Proposed Development/GradinQ
The enclosed 60 -scale topographic map indicates that the proposed development will
Background Information
An extensive geotechnical investigation was performed by Petra in 1989 (see
References). This investigation was conducted concurrently with grading of the
Redhawk Golf Course and associated interface grading of the structural fills adjacent
to the course (see References).
Purpose and Scope of Services
The purposes of this study were to obtain updated information on the subsurface
conditions within the project area, evaluate our previous investigations and the field
data, as well as provide conclusions and recommendations for design and construction
' of the proposed structures, as influenced by the subsurface conditions.
consist of an estimated total of 325 single-family residences and associated streets and
slopes.
Maximum proposed cuts and fill are approximately 26 feet. Maximum cut -slope
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height will be approximately 46 feet at a gradient of 2:1 (h:v). Maximum fill -slope
height will be approximately 50 feet at a gradient of 2:1 (h:v).
Background Information
An extensive geotechnical investigation was performed by Petra in 1989 (see
References). This investigation was conducted concurrently with grading of the
Redhawk Golf Course and associated interface grading of the structural fills adjacent
to the course (see References).
Purpose and Scope of Services
The purposes of this study were to obtain updated information on the subsurface
conditions within the project area, evaluate our previous investigations and the field
data, as well as provide conclusions and recommendations for design and construction
' of the proposed structures, as influenced by the subsurface conditions.
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THE GARRETT GROUP March 28, 2001
TRs 23066-1, -2 &-3/Temecula Area J.N. 140-01
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The scope of our investigation consisted of the following.
• Review of available published and unpublished data concerning geologic and soil
conditions within, as well as adjacent to the site that could have an impact on the
proposed development. This included review of data acquired by other engineering
firms for adjacent properties (see References).
• Geologic mapping of the site.
• Excavation, logging and selective sampling of 58 test pits to depths up to 17 feet
and four borings to a maximum depth of 35 feet. Boring and test -pit locations are
shown on Plate 1. Descriptive boring and test -pit logs, as well as boring logs from
our previous field investigation, are provided in Appendix A.
• Laboratory testing and analysis of representative samples (bulk ) obtained from the
and test pits to determine their engineering properties. Laboratory test criteria and
test results are presented in Appendix B.
Preparation of a geotechnical map (Plate 1) with respect to interpolated and
• extrapolated geologic conditions.
• Review of available reports for the subject site (see References).
• Engineering and geologic analysis of the data with respect to the proposed
development.
• An evaluation of faulting and seismicity of the region as it pertains to the site.
• Preparation of this report presenting our findings, conclusions and
recommendations for the proposed development.
INVESTIGATION AND LABORATORY TESTING
11 Field Exploration
1 Subsurface exploration was performed on February 20 through February 23, 2001, and
involved the excavation of 58 test pits to depths ranging from 3 to 17 feet utilizing a
rubber -tired backhoe. Four borings were subsequently drilled utilizing a hollow -stem
auger drill rig on March 13, 2001, to a maximum depth of 35 feet. Prior to subsurface
THE GARRETT GROUP March 28, 2001
TRs 23066-1, -2 & -3/Temecula Area J.N. 140-01
Page 4
work, an underground utilities clearance was obtained from Underground Service Alert
of Southern California.
iEarth materials encountered within the exploratory borings and test pits were classified
and logged in accordance with the visual -manual procedures of the Unified Soil
Classification System. The approximate locations of the borings and test pits are
shown on Plate 1 and descriptive test -pit logs are presented in Appendix A.
Associated with the subsurface exploration was the collection of bulk (disturbed)
samples for laboratory testing.
11 Laboratory Testin
Maximum dry density, expansion potential, soluble -sulfate analysis, soil resistivity and
pH of remolded samples were determined for selected bulk samples of soil materials
considered representative of those encountered. Moisture content and unit dry density
were also determined for in-place soil materials in representative strata. A brief
description of laboratory test criteria is given in Appendix B and all test data are
summarized on Plates B-1 through B-9. In-situ moisture content and dry unit weight
are included in the exploration logs (Plates A-1 through A-26, Appendix A). An
evaluation of the test data is reflected throughout the Conclusions and
Recommendations Section of this report.
IFINDINGS
Regional Geologic Setting
The site is located in the Peninsular Range Geomorphic Province of California.
Peninsular ranges are characterized by steep, elongated valleys that trend west to
northwest. More specifically, the property is located within the Elsinore Trough, a
fault -controlled, down -dropped graben which borders the Santa Ana Mountains on the
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ITHE GARRETT GROUP March 28, 2001
TRs 23066-1, -2 &-3/Temecula Area J.N. 140-01
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northeast and the Perris Block on the southwest. The Elsinore Trough is bounded on
the northeast by the Wildomar fault and on the southwest by the Willard fault. These
faults are part of the Elsinore fault zone which extends from the San Gabriel River
Valley to the United States/Republic of Mexico border. The Wildomar fault is
considered active and the Willard fault is considered potentially active. The site is
underlain by silty sandstones and siltstones of the Pauba Formation.
Local Geology and Soil Conditions
Earth Materials
The subject tracts are underlain with surficial deposits of undocumented fill,
compacted fill, residual soil (i.e., top soil, slope wash), Quaternary alluvium and
Quaternary colluvium(undifferentiated). These materials, in turn, are underlain with
late Pleistocene sedimentary deposits belonging to the Pauba Formation. General
descriptions of each of these earth units are given in the following paragraphs. More
detailed descriptions are presented in the appended test pit logs.
• Artificial Fill (map symbol: Afu) — Fill materials associated with golf -course
grading and grading of the surrounding tracts has produced localized stock piles
and loosely placed fill deposits composed of locally derived soil and/or Pauba
Formation bedrock materials. The maximum thickness of the localized
undocumented fill deposits are estimated at 10 feet. Furthermore, unmapped spoil
fill.also occurs in relatively minor amounts on the downslope portions of numerous
dirt roads traversing the site. Typically, the artificial fill consisted of gravelly to
silty sand with clay and a trace of cobbles which were found to be moist, loose and
contained fine- to coarse-grained sand.
• Compacted Artificial Fill (map symbol: Afc) —Structural fills have been placed
adjacent to golf -course fairways (see References) where ascending fill slopes were
ultimately planned in adjacent residential areas. Structural fills were also placed
under some fairways in future roadway areas and at the toe of ascending fill slopes.
All structural fills have been placed under the observation and testing of Petra,
which began in the late 1980s. The earth materials consisted of reddish brown to
dark brown silty sands and sandy silts with clay, which, due to recent heavy rains,
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THE GARRETT GROUP
TRs 23066-1, -2 & -3/Temecula Area
March 28, 2001
J.N. 140-01
Page 6
were found to be moist to wet, the upper 2 feet were loose to medium dense below
with fine- to coarse-grained sands and trace of roots/rootlets, cobbles and gravel.
• Top Soil (no ma1symbol) —The topsoil that blankets the lower portions of the
site consisted of dark brown, moist to very moist (locally), loose, silty sands and
sandy silts with clay. The sands were found to be fine- to coarse-grained
containing a trace of gravels and cobbles with roots and rootlets.
• Quatemary Alluvium Undifferentiated (map symbol: Qal) —Quaternary alluvial
deposits were encountered within the canyon areas throughout the site. The
deposits consisted of dark brown, fine- to coarse-grained silty sands with gravel
which were found to be loose to medium dense with a trace to rootlets and porous.
• Quaternary Colluvium Undifferentiated (map symbol: Qcol) — Quaternary
colluvium deposits composed of reddish brown to brown, dry to slightly moist
medium dense to dense, slightly porous, fine- to coarse-grained silty sands with
gravel and cobbles.
• Pauba Formation Bedrock (map symbol: Ons) —Hillside and canyon areas within
the subject site are underlain by late Pleistocene sedimentary deposits comprised
of to the Pauba Formation. This formation is composed primarily of slightly moist
to moist reddish -brown, medium dense to dense, fine- to coarse-grained
interbedded siltstone and sandstone with occasional gravel.
Groundwater
No groundwater or seepage was encountered in any of the test pits or borings
excavated for this study to a maximum depth of 35 feet.
Faulting
The geologic structure of the entire southern California area is dominated mainly by
northwest -trending faults associated with the San Andreas system. Faults, such as the
Newport -Inglewood, Whittier, Elsinore, San Jacinto and San Andreas, are major faults
in this system and all are known to be active. In addition, the San Andreas, Elsinore
and San Jacinto faults are known to have ruptured the ground surface in historic times.
THE GARRETT GROUP March 28, 2001
TRs 23066-1, -2 & -3/Temecula Area J.N. 140-01
Page 7
Based on our review of published and unpublished geotechnical maps and literature
pertaining to site and regional geology, the closest active fault to the site is the
Elsinore -Temecula fault located approximately 1.6 miles to the south.
No other active or potentially active faults project through or toward the site and the
site does not lie within an Alquist-Priolo Earthquake Fault Hazard Zone.
CONCLUSIONS AND RECOMMENDATIONS
' General
From a soils engineering and engineering geologic point of view, the subject property
is considered suited for the proposed construction, provided the following conclusions
and recommendations are incorporated into the design criteria and project
specifications.
Earthwork
General Earthwork and Grading Specifications
' All earthwork and grading should be performed in accordance with all applicable
requirements of the Grading and Excavation Code and the Grading Manual of the
County of Riverside, California, in addition to the provisions of the 1997 UBC,
including Chapter 16 and Appendix A33. Grading should also be performed in
accordance with applicable provisions of the attached Standard Grading Specifications
(Appendix D) prepared by Petra, unless specifically revised or amended herein.
Clearing and Grubbing
' All weeds, grasses, brush, shrubs and trees in areas to be graded shall be stripped and
hauled offsite. Trees to be removed should be grubbed -out such that their stumps and
tmajor -root systems are also removed and the organic materials hauled offsite. During
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' THE GARRETT GROUP March 28, 2001
TRs 23066-1, -2 &-3/Temecula Area J.N. 140-01
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site grading, laborers should clear from fills any roots, tree branches and other
deleterious materials missed during clearing and grubbing operations. Clearing
operations should also include the removal of all trash and debris existing within areas
of proposed construction and/or grading.
The project soils engineer or his qualified representative should be notified at the
appropriate times to provide observation and testing services during clearing
operations to verify compliance with the above recommendations. In addition, any
buried structures, unusual or adverse soil conditions encountered that are not described
or anticipated, herein should be brought to the immediate attention of the geotechnical
Iconsultant.
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Excavation Characteristics
Based on the results of our exploratory borings and test pits, residual soil materials and
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other surficial deposits (i.e., topsoil, colluvium, alluvium, bedrock (Pauba Formation)
and undocumented fill will be readily excavatable with conventional earthmoving
equipment. Most bedrock materials will be excavatable with moderate to heavy
ripping.
Though no impenetrable bedrock strata were encountered in the exploratory test pits
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site areas to be graded, some well -cemented strata were observed in surface outcrops
and within the older alluvium. These materials are expected to be rippable; however,
ripping of these beds may generate oversize (blocky) materials (in excess of 12 inches)
that may require special handling and placement.
Groundwater
'
No groundwater was encountered within the limits covered by this report to the depths
explored:
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THE GARRETT GROUP March 28, 2001
TRs 23066-1,-2 &-3/Temecula Area J.N. 140-01
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Ground Preparation - Fill Areas
Within the subject site, all low-density and potentially collapsible -soil materials, such
as loose manmade fill, topsoil, colluvium, alluvium and highly weathered bedrock,
will require removal to underlying dense bedrock or dense native soils from each area
to receive compacted fill. Dense native soils are defined as undisturbed native
materials with an in-place relative density of 85 percent or greater based on ASTM
Test Method D1557-91. Prior to placing structural fill, exposed bottom surfaces in
each removal area should be scarified to a depth of 6 inches or more, watered or air-
dried as necessary to achieve near optimum moisture conditions and then recompacted
in-place to a minimum relative density of 90 percent.
Based on test pits and laboratory testing, anticipated depths of removals are shown on
the enclosed geotechnical map (Plate 1). However, actual depths and horizontal limits
of removals will have to be determined during grading on the basis of in -grading
observation and testing performed by the project soils engineer and/or engineering
geologist.
The undocumented fill placed in the north -central canyon is overlying alluvium which
is subject to collapse, based on the consolidation test data performed during this study
(Appendix B). Therefore, complete removal of the documented fill and alluvium to
competent Pauba Formation bedrock will be necessary.
Canyon Subdrains
Following cleanouts to competent bedrock or approved foundation materials,
perforated plastic pipe -and -gravel canyon subdrains should be installed along the axes
of all major canyons and tributary areas where the depth of structural fill exceeds
approximately 10 feet below proposed finish pad grade. Canyon subdrains will
mitigate potential build-up of hydrostatic pressures below compacted fills due to
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THE GARRETT GROUP
TRs 23066-1,-2 &-3/Temecula Area
March 28, 2001
J.N. 140-01
Page 10
infiltration of surface waters. Subdrains should be placed as to outlet at the lowest
practical elevation. Tentative recommended locations of subdrains are shown on the
enclosed geotechnical map (Plate 1). Actual locations will have to be determined
during grading. Typical construction details are shown on Plate SG -4 (Appendix D).
Fill Placement
All fill should be placed in 6- to 8 -inch -thick -maximum lifts, watered or air-dried as
necessary to achieve near optimum moisture conditions and then compacted in-place
to a minimum relative density of 90 percent. The laboratory maximum dry density and
optimum moisture content for each change in soil type should be determined in
accordance with ASTM Test Method D1557-91.
Benching
Compacted fills placed against canyon walls and on natural -slope surfaces inclining
at 5:1 (h:v) or greater should be placed on a series of level benches excavated into
competent bedrock or dense native soils. Benching will also be required where
compacted fills are placed against temporary backcuts of recommended buttress fills
and shear keys. Typical benching details are shown on Plates SG -3, SG -4, SG -5, SG -7
and SG -8 (Appendix D).
Import Soils for Gradin
In the event import soils are needed to achieve final -design grades, all potential import
materials should be free of deleterious/oversize materials, be non -expansive and
approved by the project soils engineer prior to being brought onsite.
Processing of Cut Areas
Where low-density surfrcial deposits of topsoil, existing fill (undocumented and
compacted [weathered]), alluvium and weathered bedrock are not removed in their
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THE GARRETT GROUP March 28, 2001
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TRs 23066-1, -2 &-3/Temecula Area J.N. 140-01
Page 11
whichever is greater. Due to the previous interface grading that has occurred, the lots
egiitety in cut areas (i.e., building pads and driveways), these materials will require
overexcavation and replacement as properly compacted fill.
Cut/Fill Transition is
Shallow Fill -to -Deep -Fill Lots
_
To mitigate the potential adverse effects of differential settlement on fill lots underlain
To minimize the detithental effects of differential settlement, cut/fill transitions
should be eliminated from all.building areas where the depth of fill placed within the
"fill" portion exceeds proposed footing depths. This should be accomplished by
overexcavating the "cut" portion and replacing the excavated materials as properly
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compacted fill. Recommended depths of overexcavation are given below.
'3
ltepth of Fill12epthaf Overexcavattan
:Up to 3 feet Equal depth
3 to 6 feet ,- 3 feel
• .. Greater than feet One-half the thickness of fill placed
on the "Fill" portion (JO feet
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+ maximum)
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beyond lines
Horizontal limits of overexcavation should extend perimeter -building a
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distance equal to the depth of overexcavation or to a minimum distance of 5 feet,
whichever is greater. Due to the previous interface grading that has occurred, the lots
requiring transition -lot overexcavation will have to be determined during grading
operations.
Shallow Fill -to -Deep -Fill Lots
_
To mitigate the potential adverse effects of differential settlement on fill lots underlain
with substantial differences in compacted fill depths, the "shallow" fill portions should
be overexcavated to maintain the minimum fill depths recommended in the preceding
section.
'3
Subsidence from scarification and recompaction of exposed bottom surfaces in
removal areas to receive fill is expected to vary from negligible to approximately 0.1
foot.
IThe above estimates of shrinkage, bulking and subsidence are intended as an aid for
project engineers in determining earthwork quantities. However, these estimates
should be used with some caution since they are not absolute values. Contingencies
should be made for balancing earthwork quantities based on actual shrinkage and
subsidence that occurs during the grading operations.
ICut Slopes
' Cut slopes planned throughout the development are expected to be grossly stable to the
maximum -planned height of approximately 46 feet and at the maximum -planned
inclination of 2:1 (h:v). However, in -grading observation of individual cut slopes will
be required by the project engineering geologist to confirm favorable -geologic
structure of the exposed bedrock. Where highly fractured bedding, out -of -slope
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THE GARRETT GROUP March 28, 2001
TRs 23066-1, -2 &-3/Temecula Area J.N. 140-01
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Shrinkage. Bulking and Subsidence
Volumetric changes in earth quantities will occur when excavated onsite soil and
bedrock materials are replaced as properly compacted fill. Following is an estimate
of shrinkage and bulking factors for the various geologic units present onsite. These
estimates are based on in-place densities of the various materials and on the estimated
average degree of relative compaction achieved during grading.
• Artificial Fill (afc) ............................... Shrinkage 0 to 5%
• Artificial Fill (afu) ............................... Shrinkage 10 to 15%
• Alluvium (Qal).................................. Shrinkage 10 to 15%
• Colluvium (Qoal)................................ Shrinkage 10 to 15%
• Bedrock (Pauba Formation) ................................................. Shrinkage 0 to 5 %
Subsidence from scarification and recompaction of exposed bottom surfaces in
removal areas to receive fill is expected to vary from negligible to approximately 0.1
foot.
IThe above estimates of shrinkage, bulking and subsidence are intended as an aid for
project engineers in determining earthwork quantities. However, these estimates
should be used with some caution since they are not absolute values. Contingencies
should be made for balancing earthwork quantities based on actual shrinkage and
subsidence that occurs during the grading operations.
ICut Slopes
' Cut slopes planned throughout the development are expected to be grossly stable to the
maximum -planned height of approximately 46 feet and at the maximum -planned
inclination of 2:1 (h:v). However, in -grading observation of individual cut slopes will
be required by the project engineering geologist to confirm favorable -geologic
structure of the exposed bedrock. Where highly fractured bedding, out -of -slope
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THE GARRETT GROUP March 28, 2001
TRs 23066-1, -2 & -3/Temecula Area J.N. 140-01
Page 13
bedding, seepage or non -cemented -sand strata are observed, the cut slopes in question
may require stabilization by means of a compacted buttress or stabilization fill.
I- Fill Slopes
A basal 15 -foot -wide fill key excavated into competent bedrock will be required at the
base of all fill slopes proposed on existing ground surfaces inclining at 5:1 (h:v) or
' greater. Typical details for construction of the basal -fill key are shown on Plate SG -3
(Appendix D).
Fill -Above -Cut and Cut -to -Fill Transition Slopes
AWhere fill -above -cut slopes are proposed, a 15 -foot -wide key excavated into
competent bedrock or dense native soil should be constructed at the contact. The
bottom of the key should be tilted -back into the slope at a minimum gradient of 2
percent. A typical section for construction of fill -above -cut slopes is shown on
Plate SG -7 (Appendix D) The lower cut portion of the slope should be excavated to
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Proposed fill slopes, constructed with onsite soil and/or bedrock materials, will be
grossly and surficially stable to the heights and at the inclinations planned. A fill key
excavated a minimum depth of 2 feet into competent bedrock or dense native soil will
be required at the base of all fill slopes. The width of the fill key should equal one-half
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the slope height or 15 feet, whichever is greater. Typical fill -key construction details
are shown on Plates SG -3 and SG -7 (Appendix D).
To obtain proper compaction to the face of fill slopes, low -height fill slopes should be
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overfilled and backfilled during construction and then trimmed -back to the compacted
inner core. Where this procedure is not practical for higher slopes, final surface
compaction should be obtained by backrolling during construction to achieve proper
compaction to within 6 to 8 inches of the finish surface, followed by rolling with a
cable -lowered sheepsfoot and grid roller.
A basal 15 -foot -wide fill key excavated into competent bedrock will be required at the
base of all fill slopes proposed on existing ground surfaces inclining at 5:1 (h:v) or
' greater. Typical details for construction of the basal -fill key are shown on Plate SG -3
(Appendix D).
Fill -Above -Cut and Cut -to -Fill Transition Slopes
AWhere fill -above -cut slopes are proposed, a 15 -foot -wide key excavated into
competent bedrock or dense native soil should be constructed at the contact. The
bottom of the key should be tilted -back into the slope at a minimum gradient of 2
percent. A typical section for construction of fill -above -cut slopes is shown on
Plate SG -7 (Appendix D) The lower cut portion of the slope should be excavated to
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THE GARRETT GROUP
TRs 23066-1, -2 &-3/Temecula Area
March 28, 2001
J.N. 140-01
Page 14
grade and observed by the project engineering geologist prior to constructing the fill
portion.
Where cut -to -fill transition slopes are proposed, the fill portion should be placed on
a series of benches excavated into competent natural ground or bedrock. The benches
should be at least 8 to 10 feet wide, constructed at vertical intervals of approximately
5 feet and tilted -back into the slope at a minimum gradient of 2 percent. Where cut -to -
fill transition contacts vary from about vertical to a few degrees from vertical,
benching of the fill portion into the cut portion, as recommended above, will be
difficult and may create a potential slip surface due to inadequate benching. Therefore,
overexcavation of the cut portion and reconstruction of the entire slope with
compacted fill is recommended.
Geotechnical Observations
An observation of clearing operations, removal of unsuitable-surficial materials, cut -
and fill -slope construction and general grading procedures should be performed by the
project geotechnical consultant. Fills should not be placed without prior approval from
the geotechnical consultant.
The project geotechnical consultant or his representative should be present onsite
during all grading operations to verify proper placement and compaction of fill, as well
as to verify compliance with the other recommendations presented herein.
Post -Grading Considerations
Deep -Fill -Settlement MonitorinE
Canyon fills in excess of 50 feet in depth will require placement of settlement
monuments.
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' THE GARRETT GROUP March 28, 2001
TRs 23066-1,-2 &-3/Temecula Area J.N. 140-01
Page 15
Elevation readings of survey monuments should be made bi-weekly for the first 8
weeks and then monthly until observed settlement has reached tolerable limits.
Construction timing in areas of deep fill will be evaluated on a continuing basis, as
survey data become available.
Slope Landscaping and Maintenance
Adequate slope and pad drainage facilities are essential in the design of grading for the
subject tract. An anticipated rainfall equivalency on the order of 60 to 100± inches per
year at the site can result due to irrigation. The overall stability of the graded slopes
should not be adversely affected provided all drainage provisions are properly
constructed and maintained thereafter and provided all engineered slopes are
landscaped with a deep-rooted, drought -tolerant and maintenance -free plant species,
as recommended by the project landscape architect. Additional comments and
recommendations are presented below with respect to slope drainage, landscaping and
irrigation. A discussion of pad drainage is given in a following section.
construction and slope planting; type and spacing of plant materials used for slope
protection; rainfall intensity; and/or lack of a proper maintenance program. Based on
this discussion, the following recommendations are presented to mitigate potential
surficial slope failures.
• Proper drainage provisions for engineered slopes should consist of concrete terrace
drains, downdrains and energy dissipaters (where required) constructed in
accordance with the Grading Code of the County of Riverside. Provisions should
The most common type of slope failure in hillside areas is the surficial type and
usually involves the upper 1 to 6± feet. For any given gradient, these surficial slope
failures are generally caused by a wide variety of conditions, such as overwatering;
cyclic changes in moisture content and density of slope soils from both seasonal and
irrigation -induced wetting and drying; soil expansiveness; time lapse between slope
construction and slope planting; type and spacing of plant materials used for slope
protection; rainfall intensity; and/or lack of a proper maintenance program. Based on
this discussion, the following recommendations are presented to mitigate potential
surficial slope failures.
• Proper drainage provisions for engineered slopes should consist of concrete terrace
drains, downdrains and energy dissipaters (where required) constructed in
accordance with the Grading Code of the County of Riverside. Provisions should
THE GARRETT GROUP March 28, 2001
TRs 23066-1,-2 &-3/Temecula Area J.N. 140-01
Page 16
also be made for construction of compacted -earth berms along the tops of all
engineered slopes.
' Provided the above recommendations are followed with respect to slope drainage,
maintenance and landscaping, the potential for deep saturation of slope soils is
' considered very low.
• Homeowners should be advised of the potential problems that can develop when
drainage on the pads and slopes is altered in any way. Drainage can be altered due
to the placement of fill and construction of garden walls, retaining walls,
walkways, patios, swimming pool, spas and planters.
• All permanent engineered slopes should be landscaped as soon as practical at the
completion of grading. As noted, the landscaping should consist of a deep-rooted,
drought -tolerant and maintenance -free plant species. If landscaping cannot be
provided within a reasonable period of time, jute matting (or equivalent) or a spray -
on product designed to seal slope surfaces should be considered as a temporary
measure to inhibit surface erosion until such time permanent landscape plants have
become well-established.
• Irrigation systems should be installed on the engineered slopes and a watering
program then implemented which maintains a uniform, near optimum moisture
condition in the soils. Overwatering and subsequent saturation of the slope soils
should be avoided. On the other hand, allowing the soils to dry -out is also
detrimental to slope performance.
• Irrigation systems should be constructed at the surface only. Construction of
'
sprinkler lines in trenches should not be allowed without prior approval from the
soils engineer and engineering geologist.
• During construction of terrace and downdrains, care must be taken to avoid
placement of loose soil on the slope surfaces.
• A permanent slope -maintenance program should be initiated for major slopes not
maintained by individual homeowners. Proper slope maintenance must include the
care of drainage- and erosion -control provisions, rodent control and repair of
leaking or damaged irrigation systems.
' Provided the above recommendations are followed with respect to slope drainage,
maintenance and landscaping, the potential for deep saturation of slope soils is
' considered very low.
• Homeowners should be advised of the potential problems that can develop when
drainage on the pads and slopes is altered in any way. Drainage can be altered due
to the placement of fill and construction of garden walls, retaining walls,
walkways, patios, swimming pool, spas and planters.
' THE GARRETT GROUP March 28, 2001
TRs 23066-1, -2 &-3/Temecula Area J.N. 140-01
Page 17
Natural Slopes
Natural slopes located within the subject site are considered grossly stable. However,
surface soils are prone to downslope -soil creep and possible slumping or mudflow
under heavy -saturated conditions. Therefore, natural slopes located below daylight -cut
' lots should be protected from surface runoff and subsequent saturation of surface soil
by means of top -of -slope, compacted -earth berms. Residential structures and onsite
improvements (pools, etc.) constructed on lots bordered by ascending natural slopes
' should be protected from potential mudflow debris.
Utility Trenches
All utility -trench backfill within street right-of-ways, utility easements, under
' sidewalks, driveways and building -floor slabs, as well as within or in proximity to
slopes should be compacted to a minimum relative density of 90 percent. Where
onsite soils are utilized as backfill, mechanical compaction will be required. Density
testing, along with probing, should be performed by the project soils engineer or his
' representative, to verify proper compaction.
For deep trenches with vertical walls, backfill should be placed in approximately I-
to 2 -foot -thick maximum lifts and then mechanically compacted with a hydra -hammer,
pneumatic tampers or similar equipment. For deep trenches with sloped -walls, backfill
materials should be placed in approximately 8- to 12 -inch -thick -maximum lifts and
' then compacted by rolling with a sheepsfoot tamper or similar equipment.
' As an alternate for shallow trenches where pipe may be damaged by mechanical
compaction equipment, such as under building -floor slabs, imported clean sand having
a sand equivalent value of 30 or greater may be utilized and jetted or flooded into
place. No specific relative compaction will be required; however, observation, probing
and, if deemed necessary, testing should be performed.
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THE GARRETT GROUP March 28, 2001
TRs 23066-1,-2 &-3/Temecula Area J.N. 140-01
,. Page 18
To avoid point -loads and subsequent distress to clay, cement or plastic pipe, imported
sand bedding should be placed at least I foot above all pipe in areas where excavated
trench materials contain significant cobbles. Sand -bedding materials should be
thoroughly jetted prior to placement of backfill.
0 Where utility trenches are proposed parallel to any building footing (interior and/or
exterior trenches), the bottom of the trench should not be located within a 1:1 (h:v)
plane projected downward from the outside bottom edge of the adjacent footing.
Site Drainage
Positive -drainage devices, such as sloping sidewalks, graded-swales and/or area drains,
should be provided around each building to collect and direct all water away from the
' structures. Neither rain nor excess irrigation water should be allowed to collect or
pond against building foundations. Roof gutters and downspouts may be required on
the sides of buildings where yard -drainage devices cannot be provided and/or where
roof drainage is directed onto adjacent slopes. All drainage should be directed to
adjacent driveways, adjacent streets or storm -drain facilities.
Seismic -Design Considerations
' Ground Motions
Structures within the site should be designed and constructed to resist the effects of
' seismic ground motions as provided in the 1997 UBC, Sections 1626 through 1633.
The method of design is dependent on the seismic zoning, site characteristics,
' occupancy category, building configuration, type of structural system and building
height.
' For structural design in accordance with the 1997 UBC, a computer program
developed by Thomas F. Blake (UBCSEIS, 1998) was used that compiles fault
THE GARRETT GROUP March 28, 2001
TRs 23066-1, -2 &-3/Temecula Area J.N. 140-01
Page 19
information for a particular site using a modified version of a data file of
approximately 183 California faults that were digitized by the California Division of
Mines and Geology and the U.S. Geological Survey. This program computes various
information for a particular site including the distance of the site from each of the
'- faults in the data file, the estimated slip -rate for each fault and the "maximum moment
magnitude" of each fault. The program then selects the closest Type A, Type B and
Type C faults from the site and computes the seismic design coefficients for each of
the fault types. The program then selects the largest of the computed seismic design
coefficients and designates these as the design coefficients for the subject site.
' Based on our evaluation and fault investigation, the Elsinore -Julian (Type A) segment
of Elsinore fault zone, located approximately 12.1 kilometers from the site, would
' probably generate the most severe site ground motions with anticipated maximum
moment magnitudes of 7.1 and anticipated slip rate of 5.0 mm/year. The closest Type
B fault is the Elsinore -Temecula fault which is 1.6 kilometers from the site and would
probably generate severe site ground motions with anticipated maximum moment
' magnitudes of 6.8 and anticipated slip rate of 5.0 mm/year. The following 1997 UBC
seismic design coefficients should be used for the proposed structures. These criteria
are based on the soil profile type as determined by existing subsurface geologic
conditions, on the proximity of the Elsinore -Julian fault and on the maximum moment
magnitude and slip rate.
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THE GARRETT GROUP
TRs 23066-1, -2 & -3/Temecula Area
March 28, 2001
J.N. 140-01
Page 20
13BC Il497 tABI l lACtii12
Figure 16-2
Seismic Zone
- 4
Table 16-1
Seismic Zone Factor Z
0.4
Table 16-U
Seismic Source Type
B
Table 16-J
Soil Profile Type
Sp
Table 16-5
Near -Source Factor N.
1.2
Table 16-T
Near -Source Factor N,
1.5
Table 16-Q
Seismic Coefficient Ca
0.44 N, = 0.53
Table 16-R
Seismic Coefficient C,
0.64 Na = 0.96
Secondary Effects of Seismic Activity
Secondary effects of seismic activity normally considered as possible hazards to a site
include several types of ground failure, as well as induced flooding. Various general
types of ground failures which might occur as a consequence of severe ground shaking
at the site include landsliding, ground subsidence, ground lurching, shallow -ground
rupture and liquefaction. The probability of occurrence of each type of ground failure
depends on the severity of the earthquake, distance from faults, topography, subsoils
and groundwater conditions, in addition to other factors. Based on our subsurface
exploration, all of the above secondary effects of seismic activity are considered
unlikely at the site.
Seismically induced flooding which might be considered a potential hazard to a site
normally includes flooding due to a tsunamis (seismic sea wave), a seiche (i.e., a
wave-like oscillation of the surface of water in an enclosed basin that may be initiated
by a strong earthquake) or failure of a major reservoir or retention structure upstream
of the site. Since the site is located nearly 30 miles inland from the nearest coastline
of the Pacific Ocean at an elevation in excess of 1225 feet above mean sea level, the
potential for seismically induced flooding due to a tsunamis run-up is considered
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THE GARRETT GROUP
TRs 23066-1, -2 & -3/Temecula Area
March 28, 2001
J.N. 140-01
Page 21
nonexistent. Since no enclosed bodies of water lie adjacent to the site, the potential
for induced flooding at the site due to a seiche is also considered nonexistent.
Soil Corrosivity
Representative soil samples have been tested to determine the potential for corrosion
of metal pipes due to the soils on the site. The test results indicate that the soils are
corrosive.
This conclusion is based on the following corrosive potential from resistivity level
readings.
ltesisftvtty Level lteadutg :'
Carru5rvity Euteatral
Over 10,000
Mild
5,000 - 10,000
Moderate
1,000 - 5,000
Corrosive
500- 1,000
Very Corrosive
Under 500
Extremely Corrosive
Note: If additional information is needed, a Corrosion Engineer should be consulted.
Tentative Foundation -Design Recommendations
General
Provided site grading is performed in accordance with the recommendations of this
report, conventional shallow foundations are considered feasible for support of the
proposed residential structures. Tentative foundation recommendations are provided
herein. However, these recommendations may require modification depending on as -
graded conditions existing within the building sites upon completion of grading.
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THE GARRETT GROUP March 28, 2001
TRs 23066-1, -2 &-3/Temecula Area J.N. 140-01
Page 22
Allowable -Bearing Values
An allowable -bearing value of 1,500 pounds per square foot (psf) may be used for 24 -
inch -square pad footings and 12 -inch -wide continuous footings founded at a minimum
depth of 12 inches below the lowest adjacent final grade. This value may be increased
by 20 percent for each additional foot of width and depth, to a maximum value of
2,500 psf. Recommended allowable -bearing values include both dead and live loads
and may be increased by one-third for short -duration wind and seismic forces.
Settlement
Based on the general settlement characteristics of the compacted fill and in-situ
bedrock, as well as the anticipated loading, it has been estimated that the maximum
total settlement of conventional footings will be less than approximately 0.75 inch.
Differential settlement is expected to be about one-half the total settlement over 30
feet. It is anticipated that the majority of the settlement will occur during construction
or shortly thereafter as building loads are applied.
The above settlement estimates are based on the assumption that the grading will be
performed in accordance with the grading recommendations presented in this report
and that the project geotechnical consultant will observe or test the soil conditions in
the footing excavations.
Lateral Resistance
A passive earth pressure of 250 psf per foot of depth to a maximum value of 2,500 psf
may be used to determine lateral -bearing resistance for footings. The passive earth
pressure should be reduced to 150 psf per foot of depth to a maximum value of 1,500
psf for descending slopes. In addition, a coefficient of friction of 0.4 times the dead -
load forces may be used between concrete and the supporting soils to determine lateral
sliding resistance. The above values may be increased by one-third when designing
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' THE GARRETT GROUP March 28, 2001
' TRs 23066-1, -2 & -3/Temecula Area J.N. 140-01
Page 23
for short -duration wind or seismic forces. The above values are based on footings
placed directly against compacted fill. In the case where footing sides are formed, all
backfill placed against the footings should be compacted to a minimum of 90 percent
of maximum dry density.
Footing Setbacks From Descending Slopes
• Fill Slopes -- Where residential structures are proposed near the tops of descending
compacted fill slopes, the footing setbacks from the slope face should conform with
1997 UBC Figure 18-I-1. The required minimum setback is H/3 (one-third the
slope height) measured along a horizontal line projected from the lower outside
face of the footing to the slope face. The footing setbacks should be 5 feet
' minimum where the slope height is 15 feet or less and vary up to 40 feet maximum
where the slope height exceeds 15 feet.
• Cut Slopes --Where residential structures are proposed near the tops of descending
cut slopes composed of sound bedrock materials, the footing setbacks from the
slope face should also generally conform with 1997 UBC Figure 18-I-1.
Building Clearances From Ascending Slopes
' Building setbacks from ascending cut and fill slopes should conform with 1997 UBC
' Figure 18-I-1 that requires a building clearance of H/2 (one-half the slope height)
varying from 5 feet minimum to 15 feet maximum. The building clearance is
measured along a horizontal line projected from the toe of the slope to the face of the
building. A retaining wall may be constructed at the base of the slope to achieve the
required building clearance.
Footing Observations
All building -footing trenches should be observed by the project geotechnical
consultant to verify that they have been excavated into competent bearing soils. The
foundation excavations should be observed prior to the placement of forms,
' reinforcement or concrete. The excavations should be trimmed neat, level and square.
•
THE GARRETT GROUP March 28, 2001
' TRs 23066-1, -2 &-3/Temecula Area J.N. 140-01
Page 24
' All loose, sloughed or moisture -softened soil should be removed prior to concrete
placement.
Excavated materials from footing excavations should not be placed in slab -on -grade
areas unless the soils are compacted to a minimum of 90 percent of maximum dry
density.
Expansive Soil Considerations
' Results of preliminary laboratory tests indicate onsite soil and bedrock materials
exhibit a VERY LOW to LOW expansion potential as classified in accordance with
' Very Low Expansion Potential (Expansion Index of 20 or less
' The following recommendations pertain to as -graded lots which would exhibit a
VERY LOW expansion potential as classified in accordance with 1997 UBC
' Table 18 -I -B. Since these soils would exhibit expansion indices of less than 20, the
design of slab -on -ground foundations is exempt from the procedures outlined in 1997
' UBC Section 1815. Based on the above soil conditions, it is recommended that
footings and floors be constructed and reinforced in accordance with the following
' minimum criteria. However, additional slab thickness, footing sizes and/or
Rk
1997 UBC Table 18 -I -B; however, expansive soil conditions should be evaluated for
individual lots during and at the completion of rough grading to verify the anticipated
'
condition. The design and construction details presented below may be tentatively
considered for conventional footings and floor slabs underlain with LOW expansive
'
foundation soils but subject to possible modification depending on actual as -graded
soil conditions. Furthermore, it should be noted that additional slab thickness, footing
'
sizes and/or reinforcement more stringent than the minimum recommendations that
follow should be provided as recommended by the project architect or structural
engineer.
' Very Low Expansion Potential (Expansion Index of 20 or less
' The following recommendations pertain to as -graded lots which would exhibit a
VERY LOW expansion potential as classified in accordance with 1997 UBC
' Table 18 -I -B. Since these soils would exhibit expansion indices of less than 20, the
design of slab -on -ground foundations is exempt from the procedures outlined in 1997
' UBC Section 1815. Based on the above soil conditions, it is recommended that
footings and floors be constructed and reinforced in accordance with the following
' minimum criteria. However, additional slab thickness, footing sizes and/or
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' THE GARRETT GROUP March 28, 2001
' TRs 23066-1, -2 &-3/Temecula Area J.N. 140-01
Page 25
reinforcement should be provided as required by the project architect or structural
engineer.
• Footings
Exterior continuous footings may be founded at the minimum depths indicated
1 in 1997 UBC Table 18 -I -C (i.e. 12 -inch minimum depth for one-story and 18 -
inch minimum depth for two-story construction). Interior continuous footings
' for both one- and two-story construction may be founded at a minimum depth
of 12 inches below the lowest adjacent grade. All continuous footings should
have a minimum width of 12 and 15 inches, for one- and two-story buildings,
respectively, and should be reinforced with two No. 4 bars, one top and one
bottom.
Exterior pad footings intended for the support of roof overhangs, such as second
story decks, patio covers and similar construction, should be a minimum of 24
' inches square and founded at a minimum depth of 18 inches below the lowest
adjacent final grade. No special reinforcement of the pad footings will be
required.
Interior isolated pad footings supporting raised wood floors should be a
minimum of 24 inches square and founded at minimum depths of 12 and 18
inches below the lowest adjacent final grade for one- and two-story construction,
respectively. No special reinforcement of the pad footings will be required.
• Floor Slabs
' Living -area concrete -floor slabs should be 4 inches thick and reinforced with
either 6 -inch by 6 -inch, No. 6 by No. 6 welded -wire fabric (6x6-W2.9xW2.9
WWF) or with No.3 bars spaced a maximum of 24 inches on center, both ways.
' All slab reinforcement should be supported on concrete chairs or bricks to
ensure the desired placement near mid -depth.
Living -area concrete -floor slabs should be underlain with a moisture -vapor
' barrier consisting of a polyvinyl chloride membrane, such as 6 -mil Visqueen or
equivalent. All laps within the membrane should be sealed and at least 2 inches
' of clean sand be placed over the membrane to promote uniform curing of the
concrete.
' Garage -floor slabs should be 4 inches thick and should be reinforced in a similar
manner as living -area floor slabs. Garage -floor slabs should also be placed
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THE GARRETT GROUP March 28, 2001
TRs 23066-1, -2 &-3/Temecula Area J.N. 140-01
' Page 26
separately from adjacent wall footings with a positive separation maintained
' with 3/8 -inch -minimum, felt expansion -joint materials and quartered with
weakened -plane joints. A 12 -inch -wide grade beam founded at the same depth
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as adjacent footings should be provided across garage entrances. The grade
beam should be reinforced with a minimum of two No. 4 bars, one top and one
bottom.
- Prior to placing concrete, the subgrade soils below all concrete slab -on -grade
should be prewatered to promote uniform curing of the concrete and minimize
the development of shrinkage cracks.
Low Expansion Potential (Expansion Index of 21 to 50)
The following recommendations pertain to as -graded lots which would exhibit a LOW
expansion potential as classified in accordance with 1997 UBC Table 18-1-B. The
1997 UBC specifies that slab -on -ground foundations (floor slabs) on soils with an
expansion index greater than 20 require special design considerations in accordance
with 1997 UBC Section 1815. The design procedures outlined in 1997 UBC Section
1815 are based on a plasticity index of the different soil layers existing within the
upper 15 feet of the building site. We have assumed an effective plasticity index of
15 in accordance with 1997 UBC Section 1815.4.2.
The design and construction recommendations that follow are based on the above soil
conditions and may be considered for minimizing the effects of slightly (LOW)
expansive soils. These recommendations have been based on the previous experience
of Petra on projects with similar soil conditions. Although construction performed in
accordance with these recommendations has been found to minimize post -construction
movement and/or cracking, they generally do not positively mitigate all potential
effects of expansive soil action. The owner, architect, design civil engineer, structural
engineer and contractors must be made aware of the expansive -soil conditions which
exist at the site. Furthermore, it is recommended that additional slab thicknesses,
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' THE GARRETT GROUP March 28, 2001
' TRs 23066-1, -2 & -3/Temecula Area J.N. 140-01
Page 27
footing sizes and/or reinforcement more stringent than recommended below be
provided as required or specified by the project architect or structural engineer.
' • Footings
Exterior continuous footings may be founded at the minimum depths indicated
in 1997 UBC Table 18 -I -C (i.e., 12 -inch minimum depth for one-story and 18 -
inch minimum depth for two-story construction). Interior continuous footings
for both one- and two-story construction may be founded at a minimum depth
of 12 inches below the lowest adjacent grade. All continuous footings should
have a minimum width of 12 and 15 inches, for one- and two-story buildings,
' respectively, and should be reinforced with two No. 4 bars, one top and one
bottom.
Exterior pad footings intended for the support of roof overhangs, such as second
story decks, patio covers and similar construction, should be a minimum of 24
inches square and founded at a minimum depth of 18 inches below the lowest
adjacent final grade. The pad footings should be reinforced with No. 4 bars
spaced a maximum of 18 inches on centers, both ways, near the bottom -third of
' the footings.
' Interior isolated pad footings supporting raised -wood floors should be a
minimum of 24 inches square and founded a minimum depth of 12 and 18
inches below the lowest adjacent final grade for one- and two-story construction,
' respectively. The pad footings should be reinforced with No. 4 bars spaced a
maximum of 18 inches on centers, both ways, near the bottom one-third of the
footings.
' Floor Slabs
' The project architect or structural engineer should evaluate minimum floor -slab
thickness and reinforcement in accordance with 1997 UBC Section 1815 based
on an effective plasticity index of 15. Unless a more stringent design is
recommended by the architect or the structural engineer, we recommend a
minimum slab thickness of inches for both living -area and garage -floor slabs
' and reinforcing consisting of either 6 -inch by 6 -inch, No. 6 by No. 6 welded -
wire fabric (6x6-W2.9xW2.9 WWF) or No. 3 bars spaced a maximum of 18
inches on centers, both ways. All slab reinforcement should be supported on
' concrete chairs or bricks to ensure the desired placement near mid -height.
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THE GARRETT GROUP March 28, 2001
TRs 23066-1,-2 &-3/Temecula Area J.N. 140-01
' Page 28
Living -area concrete -floor slabs should be underlain with a moisture -vapor
' barrier consisting of a polyvinyl chloride membrane, such as 6 -mil Visqueen or
equivalent. All laps within the membrane should be sealed and at least 2 inches
of clean sand be placed over the membrane to promote uniform curing of the
concrete.
Garage -floor slabs should also be placed separately from adjacent wall footings
with a positive separation maintained with 3/8 -inch -minimum, felt expansion -
joint materials and quartered with weakened -plane joints. A 12 -inch -wide grade
' beam founded at the same depth as adjacent footings should be provided across
garage entrances. The grade beam should be reinforced with a minimum of two
No. 4 bars, one top and one bottom.
Prior to placing concrete, the subgrade soils below all living -area and garage -
floor slabs should be pre -watered to achieve a moisture content that is at least
equal to or slightly greater than optimum -moisture content. This moisture
content should penetrate to a minimum depth of 12 inches into the subgrade
' soils.
Post-Tensionine
In lieu of the above recommendations, a post -tensioned system may be considered.
The actual design of post -tensioned footings and slabs is referred to the project
' structural engineer.
To assist the structural engineer in his design, the following parameters are
' recommended.
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TRs 23066-1, -2 & -3/Temecula Area
March 28, 2001
J.N. 140-01
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Design Specifications for Post -Tensioning Institute
Assumed percent clay
30
Clay type
Mommorillorme
Approximate depth of constant suction (feet)
7.0
Approximate soil suction (pF)
3.6
Approximate velocity or moisture now (inchestmonth)
0.7
Thornwaite Index
-20
Average edge
Moisture variation
depth, e,,,
(feet)
Center lift
4.6
Edge lift
2.2
Anticipated swell, y,,,
(inches)
Center lift
1.4
Edge lift
0.4
• Perimeter footings for either one- or two-story dwellings may be founded at a
' minimum depth of 12 inches below the nearest adjacent final -ground surface.
Interior footings may be founded at a minimum depth of 12 incites below the top
of the finish -floor slab.
' • All dwelling -area -floor slabs constructed on -grade should be underlain with a
moisture -vapor barrier consisting of a polyvinyl -chloride membrane, such as 6 -
mil visqueen. A minimum of 1 inch of clean sand should be placed over the
membrane to promote uniform curing of the concrete.
1 • Presaturation of subgrade soils below slabs -on -grade will not be required.
However, subgrade soils should be thoroughly moistened prior to placing
concrete.
Retaining Walls
Footing Embedments
The base of retaining -wall footings constructed on level ground may be founded at a
minimum depth of 12 inches below the lowest adjacent final grade into approved
competent native soils or undisturbed bedrock materials . Where retaining walls are
THE GARRETT GROUP March 28, 2001
' TRs 23066-1, -2 &-3/Temecula Area J.N. 140-01
Page 30
proposed on or within 15 feet from the top of any adjacent descending fill slope, the
footings should be deepened such that a minimum horizontal clearance of 15 feet is
maintained between the outside bottom edges of the footings and the face of the slope.
This horizontal structural setback may be reduced to 10 feet where footings are
constructed near the tops of descending cut slopes. The above recommended
minimum footing setbacks are preliminary and may be revised based on site-specific
soil and/or bedrock conditions. All footing trenches should be observed by the project
geotechnical representative to verify that the footing trenches have been excavated into
'. competent -bearing soils and/or bedrock and to the minimum embedments
recommended above. These observations should be performed prior to placing forms
or reinforcing steel.
Active and At -Rest Earth Pressures
'
An active lateral -earth pressure equivalent fluid having a density of 35 pounds per
cubic foot (pcf) should tentatively be used for design of cantilevered walls retaining
'
a drained level backfill. Where the wall backfill slopes upward at 2:1 (h:v), the above
value should be increased to 53 pcf. All retaining walls should be designed to resist
'
any surcharge loads imposed by other nearby walls or structures in addition to the
above active earth pressures.
For design of retaining walls that are restrained at the top, an at -rest earth pressure
'
equivalent to a fluid having density of 53 pcf should tentatively be used for walls
supporting a level backfill. This value should be increased to 78 pcf for an ascending
t2:1
(h:v) backfill.
Drainage
Weepholes or open vertical masonry joints should be provided in retaining walls to
'
prevent entrapment of water in the backfill. Weepholes, if used, should be 3 inches in
1 It
' THE GARRETT GROUP March 28, 2001
TRs 23066-1, -2 &-3/Temecula Area J.N. 140-01
Page 31
' minimum diameter and provided at minimum intervals of 6 feet along the wall. Open
vertical masonry joints, if used, should be provided at 32 -inch -minimum intervals. A
' continuous gravel fill, 12 inches by 12 inches, should be placed behind the weepholes
or open masonry joints. The gravel should be wrapped in filter fabric to prevent
infiltration of fines and subsequent clogging of the gravel. Filter fabric may consist
of Mirafi 140N or equal.
' In lieu ofweepholes or open joints, a perforated pipe -and -gravel subdrain may be used.
' Perforated pipe should consist of 4 -inch -minimum diameter PVC Schedule 40 or ABS
SDR -35, with the perforations laid down. The pipe should be embedded in 1.5 cubic
feet per foot of 0.75- or 1.5 -inch open -graded gravel wrapped in filter fabric. Filter
fabric may consist of Mirafi 140N or equal.
' The outside portions of retaining walls supporting backfill should be coated with an
' approved waterproofing compound to inhibit infiltration of moisture through the walls.
' Temporary Excavations
To facilitate retaining -wall construction, the lower 5 feet of temporary slopes may be
' cut vertical and the upper portions exceeding a height of 5 feet should be cut back at
a maximum gradient of 1:1 (h:v) for the duration of construction. However, all
' temporary slopes should be observed by the project soils engineer for any evidence of
' potential instability. Depending on the results of these observations, flatter slopes may
be necessary. The potential effects of various parameters such as weather, heavy
' equipment travel, storage near the tops of the temporary excavations and construction
scheduling should also be considered in the stability of temporary slopes.
I
THE GARRETT GROUP March 28, 2001
TRs 23066-1, -2 & -3/Temecula Area J.N. 140-01
11 Page 32
Wall Backfill
All retaining -wall backfill should be placed in 6- to 8 -inch -maximum lifts, watered or
air-dried as necessary to achieve near optimum moisture conditions and compacted in
place to a minimum relative compaction of 90 percent.
Construction on or Near the Tops of Descending Slopes
Continuous footings for masonry block garden walls proposed on or within 7 feet from
the top of any descending cut or fill slope should be deepened such that a minimum
horizontal clearance of 7 feet is maintained between the outside bottom edge of the
' footing and the slope face. The footings should be reinforced with a minimum of two
No. 4 bars, one top and one bottom. Plans for any top -of -slope garden walls proposing
pier and grade -beam footings should be reviewed by the project geotechnical
consultant prior to construction.
Construction on Level Ground
Where masonry walls are proposed on level ground and at least 7 feet from the tops .
of descending slopes, the footings for these walls may be founded at a minimum depth
of 12 inches below the lowest adjacent final grade. These footings should also be
reinforced with a minimum of two No. 4 bars, one top and one bottom.
Construction Joints
In order to mitigate the potential for unsightly cracking related to the effects of
' differential settlement, positive separations (construction joints) should be provided
in the walls at horizontal intervals of approximately 25 feet and at each corner. The
' separations should be provided in the blocks only and not extend through the footings.
The footings should be placed monolithically with continuous rebars to serve as
' effective "grade beams" along the full lengths of the walls.
THE GARRETT GROUP March 28, 2001
TRs 23066-1, -2 &-3/Temecula Area J.N. 140-01
Page 33
Preliminary Structural -Pavement Design
An R -value test was performed during the investigation on a selected sample; based
on Petra's experience on projects with similar soil and bedrock conditions, it is
anticipated that the subgrade materials that will exist with the street areas at the
completion of rough grading will exhibit R -values in excess of 20. Therefore,
assuming a conservative R -value of 20 for street subgrade materials and considering
Traffic Indices of 7.0 for collector streets, 6.0 for interior streets and 5.0 for cul-de-
sacs, the following tentative pavement -design sections have been prepared for
preliminary planning purposes.
Notes:
AC = Asphaltic Concrete (feet)
AB = Aggregate Base (feet)
Subgrade soils immediately below the AB should be compacted to a minimum of 95
percent relative compaction based on ASTM Test Method D1557 to a depth of 12
inches or more. Final subgrade compaction should be performed prior to placing AB
and after all utility -trench backfills have been compacted and tested.
AB materials should consist of Class 2 AB conforming to Section 26-1.02B of the
State of California (Caltrans) Standard Specifications of either crushed AB, crushed
miscellaneous base or processed miscellaneous base conforming to Section 200-2 of
the Standard Specifications for Public Works Construction (Greenbook). AB materials
THE GARRETT GROUP
TRs 23066-1, -2 &-3/Temecula Area
March 28, 2001
J.N. 140-01
Page 34
should be compacted to a minimum of 95 percent relative compaction based on ASTM
Test Method D1557. AC materials and construction should conform to Section 203
of the Greenbook.
Additional R -value sampling should be performed upon completion of rough and post
grading. Additional testing could reduce the overall pavement thickness.
Concrete Flatwork
Thickness and Joint Spacing
To reduce the potential of unsightly cracking, concrete sidewalks and patio -type slabs
should be at least 4 inches thick and provided with construction or expansion joints
every 6 feet or less. Concrete driveway slabs should be at least 4 inches thick and
provided with construction or expansion joints every 10 feet or less.
Subgrade Preparation
As a further measure to minimize cracking of concrete flatwork, the subgrade soils
below concrete-flatwork areas should first be compacted to a minimum relative density
of 90 percent and then thoroughly wetted to achieve a moisture content that is at least
equal or slightly greater than optimum moisture content. This moisture should extend
to a depth of 12 inches below subgrade and maintained in the soils during placement
of concrete. Pre -watering of the soils will promote uniform curing of the concrete and
minimize the development of shrinkage cracks. A representative of the project soils
engineer should observe and verify the density and moisture content of the soils and
the depth of moisture penetration prior to placing concrete.
Planters
Area drains should be extended into all planters that are located within 5 feet of
building walls, foundations, retaining walls and masonry -block garden walls to
THE GARRETT GROUP March 28, 2001
' TRs 23066-1,-2 & -3/Temecula Area J.N. 140-01
Page 35
minimize excessive infiltration of water into the adjacent foundation soils. The surface
' of the ground in these areas should also be sloped at a minimum gradient of 2 percent
away from the walls and foundations. Drip -irrigation systems are also recommended
to prevent overwatering and subsequent saturation of the adjacent foundation soils.
Soluble -Sulfate Analyses
' Laboratory test data indicate site soils contain varying amounts with some soils
indicating 0.19 percent water-soluble sulfates. Therefore, according to 1997 UBC
' Table 26-A-6, no special Type II Portland cement will be required for concrete to be
placed in contact with onsite soils.
This recommendation is based on three samples collected during this preliminary
' investigation and past investigations (references) and grading of the subsurface soils.
The initiation of grading at the site could blend various soil types and import soils may
' be used locally. These changes made to the foundation soils could alter sulfate -content
levels. Accordingly, it is recommended that additional testing be performed at the
completion of grading to verify sulfate contents.
GRADING -PLAN REVIEW AND CONSTRUCTION SERVICES
' This report has been prepared for the exclusive use of The Garrett Group, LLP to assist
' the project engineer and architect in the design of the proposed development. It is
recommended that Petra be engaged to review the final -design drawings and
' specifications prior to construction. This is to verify that the recommendations
contained in this report have been properly interpreted and are incorporated into the
' project specifications. If Petra is not accorded the opportunity to review these
documents, we can take no responsibility for misinterpretation of our
' recommendations.
TiC�3o �1�, -/
1`
11.
1
THE GARRETT GROUP
TRs 23066-1, -2 &-3/Temecula Area
March 28, 2001
J.N. 140-01
Page 36
We recommend that Petra be retained to provide soil -engineering services during
construction of the excavation and foundation phases of the work. This is to observe
compliance with the design, specifications or recommendations and to allow design
changes in the event that subsurface conditions differ from those anticipated prior to
start of construction.
If the project plans change significantly (e.g., building loads or type of structures), we
should be retained to review our original design recommendations and their
applicability to the revised construction. If conditions are encountered during
construction that appear to be different than those indicated in this report, this office
should be notified immediately. Design and construction revisions may be required.
INVESTIGATION LIMITATIONS
This report is based on the project, as described and the geotechnical data obtained
from the field tests performed at the locations indicated on the plan. The materials
encountered on the project site and utilized in our laboratory investigation are believed
representative of the total area. However, soils can vary in characteristics between
excavations, both laterally and vertically.
The conclusions and opinions contained in this report are based on the results of the
described geotechnical evaluations and represent our best professional judgement. The
findings, conclusions and opinions contained in this report are to be considered
tentative only and subject to confirmation by the undersigned during the construction
process. Without this confirmation, this report is to be considered incomplete and
Petra or the undersigned professionals assume no responsibility for its use. In
addition, this report should be reviewed and updated after a period of 1 year or if the
site ownership or project concept changes from that described herein.
Z
THE GARRETT GROUP March 28, 2001
TRs 23066-1, -2 &-3/Temecula Area J.N. 140-01
Page 37
This report has not been prepared for use by parties or projects other than those named
or described above. It may not contain sufficient information for other parties or other
purposes.
The professional opinions contained herein have been derived in accordance with
current standards of practice and no warranty is expressed or implied.
Respectfully submitted,
PUTR A (P0TFCHN1C'A1. INC.
Stephen M.
Senior Ass(
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SITE LOCATION MAP
REFERENCE: & PETRA GEOTECHNICAL, INC.
U.S.G.S. topographic map, NORTH
7.5 minute series, Pechanga 0 2000 FEET JN 140-01 MAR., 2001
quadrangle, dated 1968,
photorevised 1988. SCALE FIGURE 1
Bartlett, S.F., and Youd, T.L., 1995, "Empirical prediction of Liquefaction -Induced Lateral Spread," American Society
of Civil Engineers, Journal of Geotechnical Engineering, vol. 121, n. 4, pp. 316-3295.
Blake, T.F., 1998a, "FRISKSP" - A Complete Program for the Probabilistic Estimation of Seismic Hazard Using
Faults and Earthquake Sources Version 3.OB.
, 1998b, "UBCSEIS" - A Computer Program for the Deterministic Prediction of Anticipated Maximum
Moment Magnitude (Mw) and an Anticipated Slip Rate.
., 1998d, "LIQUEFY 2", a Computer Program for the Empirical Prediction of Earthquake -Induced
Liquefaction Potential, Version 1.50.
Campbell, K.W., and Bozorgnia, Y., 1994, "Near -Source Attenuation of Peak Horizontal Acceleration from Worldwide
Accelograms Recorded from 1957 to 1993"; Proceedings, Fifth U.S. National Conference on Earthquake
Engineering, Vol. III, Earthquake Engineering Institute, pp. 283-292.
Campell, K.W., 1994, Near Source Attenuation of Peak Horizontal Acceleration from Worldwide Accelerograms
Recorded 1957 to 1993: Proceedings of the Fifth U.S. National conference on Earthquake Engineering, Vol.
III, Earthquake Engineering Institute, pp. 283-292.
, 1997, Empirical Near -Source Attenuation Relationships for Horizontal and Vertical Components of Peak
Ground Acceleration, Peak Ground Velocity and Pseudo -Absolute Acceleration Response Spectra,
Seismological Research Letters, Vol. 68, No. 1, pp. 154-179.
Envicom and County of Riverside Planning Department, 1976, County of Riverside Seismic Safety and Safety Elements,
September 1976.
Hart, Earl W. and William, A. Bryant, 1997, Fault -Rupture Hazard Zones in California, Alquist-Priolo Earthquake Fault
Zoning Act with Index to Earthquake Fault Zones Map, Special Publication 42, Revised 1997, Supplements 1
and 2 added 1999.
Idriss, I.M., 1988, An update of the Simplified Liquefaction Evaluation Procedure,presentation Notes, Second Japan
Turkey Workshop, Istanbul Technical University, February 23-25, 21pp.
International Conference of Building Officials, 1997, Uniform Building Code, Volume 2, Structural Engineering
Design Provisions, dated April 1997.
, 1998, Maps of Known Active Fault Near -Source Zones in California and Adjacent Portion of Nevada,
February 1998.
Ishihara, K., 1985, "Stability of Natural Deposits During Earthquakes," Proceedings of the Eleventh International
Conference on Soil Mechanics and Foundation Engineering, San Francisco, CA, Volume 1, pp. 321-376,
August 1985.
Jenkins, Olaf P., 1966, Geologic Map of California, Santa Ana Sheet, Scale 1:250,000, California Division of Mines
and Geology, GAM019.
PETRA GEOTECHNICAL, INC. MARCH 2001
J.N. 140-01
(Continued)
Jennings, C.W., 1985, an Explanatory Text to Accompany the 1;750,000 Scale Fault and Geologic Maps of California,
California division of Mines and Geology, Bulletin No. 201.
, 1985, An Explanatory Text to Accompany the 1:750,000 Scale Fault and Geologic maps of California:
Bulletin 201, California Department of Conservation, Division of Mines and Geology.
, 1994, Fault Activity Map of California and Adjacent Areas, Corridor Design Management Group, Map
No. 6, Scale 1:750,000'.
Kennedy, Michael P., 1977, Recency and Character of Faulting along theElsinore Fault Zone in Southern Riverside
County, California, Corridor Design Management Group Special Report 131.
Michell, J.K., 1977, Soil Property Correlations, Recent Developments in the Understanding and Characterization of
Soil Properties, Woodward -Clyde Consultants' Symposium, July 1977.
National Center for Earthquake Engineering Research (NCEER), 1997, Proceedings of NCEER Workshop on
Evaluation of Liquefaction Resistance of Soils; Technical Report NCEER-98-XXXX, submittal dated
November 19, 1997.
Petra Geotechnical, Inc„ 1989, Supplemental Soils Engineering and Engineering Geologic Investigation, Portion of
' Redhawk Project, Vesting Tentative Tract Map Nos. 23064, 23065, 23066 and 23067, Rancho California,
County of Riverside, California, Volumes I and Il; for Great American Development Company, J.N. 298-87,
dated May 8, 1989.
' Seed, H.B., Tokimatsu, K., Harder, L.F., and Chung, R.M., 1985, "Influence of SPT Procedures in Soil
Liquefaction Resistance Evaluations", Journal of the Geotechnical Engineering Division, ASCE, Vol. 111,
No. GT12, pp. 1425-1445.
' State of California Department of Water Resources, 1971, Water Wells and Springs in the WestemPart of the Upper
Santa Margarita River Watershed, Riverside and San Diego Counties, California, USGS Bulletin No.91-20,
' dated August 1971.
State of California, 1990, Special Studies Zone, Pechanga Quadrangle, dated January 1, 1990.
' Youd, T.L. and Idriss, I.M., (eds.), 1997, Summary Report Proceedings of the NCEER Workshop on Evaluation
of Liquefaction Resistance of Soils, National Center for Earthquake Engineering research Technical Report
NCEER-97-0022, pp. 1040.
1.
PETRA GEOTECHNICAL, INC. MARCH 2001
J.N. 140-01