HomeMy WebLinkAboutTract Map 26828-1 Geotechnical Report Rough Grading
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e PETRA
OFFICES IN THE COUNTIES OF
ORANGE . SAN DIEGO . RIVERSIDE . LOS ANGELES . SAN BERNARDINO
September 18, 2003
J.N.217-03
RECEIVED
OCT 1 4 2003
RICHMOND AMERICAN HOMES
100 East San Marcos Boulevard, Suite 100
San Marcos, California 92069
CITY OF TEMECULA
ENGINEERING DEPARTMENT
Attention: Mr. Brian Nesteroff
Subject: Geotechnical Report of Rough Grading, Model Lots 26 through 30,
Tract 26828-1, City of Temecula, Riverside County, California
This report presents a summary of the observation and testing services provided by
Petra Geotechnical, Inc. (Petra) during rough-grading operations to develop Model
Lots 26 through 30 within Tract 26828-1 located in the City of Temecula, California.
Conclusions and recommendations pertaining to the suitability of the grading for the
proposed residential construction are provided herein, as well as foundation-design
recommendations based on the as-graded soil conditions.
The purpose of rough grading was to construct six level grading pads for construction
of single-family residences. Rough grading of the subject lots was performed between
August 2003 and September 2003. Geotechnical conditions at the site prior to rough
grading were described in our referenced supplemental geotechnical investigation
report. Site grading within the remaining portions of Tract 26828-1 is ongoing and
will be reported upon completion.
REGULATORY COMPLIANCE
Cuts, removals of unsuitable low-density surface soils, lot overexcavations and
placement of compacted fill under the purview of this report have been completed
under the observation and with selective testing by Petra. The earthwork was
PETRA GEOTECHNICAL, INC.
41640 Corning Place . Suite 107 . Murrieta . CA 92562 . Tel: (909) 600-9271 . Fax: (909) 600-9215
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RICHMOND AMERICAN HOMES
TR 26828-1 Lots 26-30/Temecula
September 18,2003
J.N. 217-03
Page 2
performed in accordance with the recommendations presented in previous geotechnical
reports by Petra (see References) and the Grading Code of the City of Temecula.
The completed earthwork has been reviewed and is considered adequate for the
construction now planned. On the basis of our observations, as well as field and
laboratory testing, the recommendations presented in this report were prepared in
conformance with generally accepted professional engineering practices and no further
warranty is implied nor made.
SUMMARY OF AS-GRADED SOIL AND GEOLOGIC CONDITIONS
As-Graded Conditions
Grading operations within Lots 26 through 30 involved the removal of low-density
surficial soils that included topsoil, alluvial and colluvial soils subject to hydrocollapse
or excessive consolidation, as well as near-surface weathered bedrock materials, and
bringing the overexcavated areas to design elevation with compacted fill. The
compacted fills ranged in depth from approximately 12 to 30 feet. A lot-by-Iot
sunnnary ofthe compacted-fill depths and a summary of soil conditions is presented
in the attached Table 1. A general description of the soil and bedrock materials
underlying the subject lots following rough grading is provided below.
. Compacted Engineered Fill (map symbol afc) - The compacted-fill soils placed
were comprised of onsite-derived soil and bedrock materials. Fill consisted
generally of fine to coarse sand, silty sand and clayey sand.
. Pauba Formation Bedrock (Qps) - The underlying Pauba Fonnation consisted of
moderately hard to hard, fme-grained and well-graded sandstone, silty sandstone
and clayey sandstone with occasional gravel, sandy siltstone, claystone and cobble
beds.
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RICHMOND AMERICAN HOMES
TR 26828-1 Lots 26-30/Temecula
September 18,2003
J.N.217-03
Page 3
SUMMARY OF EARTHWORK
OBSERVATIONS AND DENSITY TESTING
Clearing and Grubbing
At the time of grading, a majority of the tract was covered with grasses and weeds.
This vegetation was removed during overexcavation. Heavy vegetation that existed
in local areas, as well as some construction debris, were removed from the site.
Ground Preparation
Prior to placing structural fill, existing low-density surficial soils were first removed
to competent unweathered bedrock. Removals throughout the lots varied from
approximately 6 to 20 feet.
Prior to placing fill, exposed bottom surfaces in removal areas were first observed and
approved by our project geologist or senior soil technician. Following this approval,
the exposed bottom surfaces were scarified to depths of approximately 6 to 8 inches,
moisture-conditioned as necessary and compacted by rolling with pneumatic-tired
compactors, sheepsfoot rollers and loaded scrapers.
Fill Placement and Testing
Fill soils were placed in lifts restricted to approximately 6 to 8 inches in maximum
thickness, moisture-conditioned as necessary to achieve near-optimum moisture
conditions and compacted. Compaction was achieved by rolling with large self-
propelled pneumatic-wheeled compactors, sheepsfoot rollers and loaded scrapers. The
vertical depth offill placed within the subject lots was up to approximately 30 feet on
Lot 30.
Field density and moisture content tests were performed in accordance with nuclear-
gauge test methods (ASTM D2922 and D3017). Field density tests were also
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RICHMOND AMERICAN HOMES
TR 26828-1 Lots 26-30/Temecula
September 18, 2003
J.N.217-03
Page 4
performed in accordance with the sandcone method (ASTM DI556). Field density test
results obtained within the subject lots are presented in the attached Table II and
approximate test locations are shown on the enclosed Geotechnical Map with Density
Test Locations (Figure I). Results of field density tests from other portions of the
subject tract will be presented in a separate report upon completion of rough grading.
Field density tests were taken at vertical intervals of approximately I to 2 feet and the
compacted fills were tested at the time of placement to document that the specified
moisture content and relative compaction of 90 or more percent had been achieved.
Approximately one in-place density test was taken for each 1,000 cubic yards of fill
placed and/or for each 2 feet in vertical height of compacted fill. The actual number
of tests taken per day varied with the project conditions, such as the number of
earthmovers (scrapers) and availability of support equipment. When field density tests
produced results less than a relative compaction of90 percent or if the soils were found
to be excessively above or below optimum moisture content, the approximate limits
of the substandard fill were established. The substandard area was then either removed
or reworked in-place.
Visual classification of earth materials in the field was the basis for determining which
maximum dry density value was applicable for a given density test. Single-point
checks were performed to supplement visual classification.
Fill Slopes
Fill slopes were constructed at a ratio of approximately 2:1 (h:v) and to heights of up
to approximately 10 feet. The graded-fill slopes were overfilled during construction
and then track-walked to achieve compaction to the slope face. Fill slopes were
constructed on level keys which were approximately 15 feet wide and excavated into
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RICHMOND AMERICAN HOMES
TR 26828-1 Lots 26-30/Temecula
September 18, 2003
J.N.217-03
Page 5
Pauba Formation bedrock. The fill slopes are considered grossly and surficially stable
to the heights and inclinations at which they are constructed.
Cut Slopes
No cut slopes are located within the subject Lots 26 through 30.
LABORATORY TESTING
Maximum Dry Density
Maximum dry density and optimum moisture content of representative samples of the
fill soils were determined in our laboratory in accordance with ASTM D1557. The
results of these tests are presented in Appendix A.
Expansion Index Tests
Expansion index tests were performed on representative samples of soil near finish-
pad grade within the subj ect lots. These tests were performed in accordance with
ASTM D4829. Test results are also summarized in Appendix A.
Soluble Sulfate Analyses
Soluble sulfate analyses were determined for representative samples of soil existing
at or near finish grade within the subject lots. These tests were performed in
accordance with California Test Method No. 417. Test results are sunnnarized in
Appendix A.
Chloride. Resistivity and pH Analyses
Water-soluble chloride concentration, resistivity and pH were determined for selected
soil samples in accordance with California Test Method Nos. 422 (chloride) and 643
(resistivity and pH). The results of these analyses are summarized in Appendix A.
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RICHMOND AMERICAN HOMES
TR 26828-1 Lots 26-30/Temecula
September 18,2003
J.N. 217-03
Page 6
Atterberg Limits
The plasticity index of a selected sample was determined in accordance with ASTM
D4318. The results of this test are presented in Appendix A.
FOUNDATION-DESIGN RECOMMENDATIONS
Foundation Types
Based on as-graded soil and geologic conditions, the use of conventional shallow-
spread foundations is considered feasible for the proposed residential structures.
Recommended design parameters are provided herein.
Allowable Soil-Bearing Capacities
An allowable soil-bearing capacity of 1,500 pounds per square foot (pst) may be used
for 24-inch square pad footings and 12-inch wide continuous footings founded at a
depth of 12 or more inches below the lowest adjacent final grade. This value may be
increased by 20 percent for each additional foot of width or depth, to a maximum value
of 2,500 psf. Recommended allowable soil-bearing values include both dead and live
loads and may be increased by one-third when designing for short-duration wind and
seismic forces.
Anticipated Settlement
Based on the general settlement characteristics of the compacted fill soils, as well as
the anticipated loading, it has been estimated that the settlement of building footings
will be less than approximately 3/4 inch. Differential settlement over a horizontal
distance of 30 feet is expected to be about one-half the total settlement. The
anticipated differential settlement may be expressed as an angular distortion of 1:960.
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RICHMOND AMERICAN HOMES
TR 26828-1 Lots 26-30/Temecula
September 18, 2003
J.N.217-03
Page 7
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 building footings. Where
structures such as masonry block walls and retaining walls are planned on or near
descending slopes, the passive earth pressure should be reduced to 150 psfper foot of
depth to a maximum value of 1,500 psf. An increase of one-third of the above values
may also be used when designing for short-duration wind and seismic forces. In
addition a coefficient of friction of 0.40 times the dead-load forces may also be used
between concrete and the supporting soils to determine lateral-sliding resistance.
The above values are based on footings placed directly against compacted fill. In the
case where footing sides are formed, all backfill against the footings should be
compacted to a minimum of90 percent of maximum dry density.
Structural Setbacks from Descending Slopes
Where structures are proposed near the top of descending slopes, the footing setback
from the slope face should conform with 1997 Uniform Building Code (UBe)
Figure 18-1-1. The required setback is Hl3 (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 setback should be 5 feet or more where the slope height is 15 feet or less
and vary up to 40 feet where the slope height exceeds 15 feet.
Footing Observations
All footing trenches should be observed by a representative of Petra to document that
they have been excavated into competent-bearing soils and to the minimum
embedments recommended herein. The foundation excavations should be observed
prior to the placement of forms, reinforcement or concrete. The excavations should
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RICHMOND AMERICAN HOMES
TR 26828-1 Lots 26-30/Temecula
September 18, 2003
J.N.217-03
Page 8
be trimmed neat, level and square. Loose, sloughed or moisture-softened soil and
construction debris should be removed prior to placing concrete.
Excavated soils derived from footing and utility-trench excavations should not be
placed in slab-on-grade areas unless the soils are compacted to 90 or more percent of
maximum dry density.
Expansive Soil Considerations
Results of laboratory tests indicate onsite soil and bedrock materials exhibit VERY
LOW to LOW expansion potentials as classified in accordance with 1997 UBC
Table 18-I-B. A lot-by-Iot breakdown for the different levels of expansion is provided
below. Design and construction details for the various levels of expansion potential
are provided in the following sections.
Verv Low Expansion Potential (Expansion Index of20 or less)
The following recommendations pertain to as-graded Lot 26 where the foundation soils
exhibit a VERY LOW expansion potential as classified in accordance with 1997 UBC
Table 18-I-B. For soils exhibiting expansion indices ofless than 20, the design of
slab-on-ground foundations is exempt from the procedures outlined in 1997 UBC
Section 1815. Based on this soil condition, it is recommended that footings and floors
be constructed and reinforced in accordance with the following criteria. However,
additional slab thickness, footing sizes and/or reinforcement should be provided as
required by the project architect or structural engineer.
. Footings
- Standard depth footings may be used with respect to building code requirements
for the planned construction (i.e., 12 inches deep for one-story construction and
18 inches deep for two stories). Interior continuous footings for two-story
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RICHMOND AMERICAN HOMES
TR 26828-1 Lots 26-30/Temecula
September 18,2003
J.N.217-03
Page 9
construction may be founded at a depth of 12 inches or greater below the top of
slab.
_ Continuous footings should be reinforced with two No.4 bars, one top and one
bottom.
_ Isolated pad footings should be 24 inches or more square and founded at a depth
of 12 inches or more below the lowest adjacent final grade.
. Floor Slabs
_ Living-area concrete-floor slabs should be 4 inches or more thick and reinforced
with either 6x6/WI.4xWI.4 welded-wire mesh or with No.3 bars spaced 24
inches on-centers, both ways. Slab reinforcement should be supported on chairs
or bricks so that the desired placement is near mid-depth.
_ Living-area concrete floors should be underlain with a moisture-vapor retarder
consisting of I O-millimeter thick polyethylene membrane or equivalent. Two
inches or more of clean sand should be placed over the membrane to promote
uniform curing of the concrete.
Garage-floor slabs should be 4 inches or more thick and placed separately from
adjacent wall footings with a positive separation maintained with 3/8 inch 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
two No.4 bars, one top and one bottom.
- Prior to placing concrete, sub grade soils should be thoroughly moistened to
promote uniform curing of the concrete and reduce the development of
shrinkage cracks.
Low Expansion Potential (Expansion Index of 21 to 50)
The following recommendations pertain to as-graded Lots 27 through 30 where the
foundation soils exhibit a LOW expansion potential as classified in accordance with
1997 UBC Table 18-I-B. The 1997 UBC specifies that slab-on-ground foundations
(floor slabs) resting on soils with an expansion index greater than 20 require special
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RICHMOND AMERICAN HOMES
TR 26828-1 Lots 26-30/Temecula
September 18, 2003
J.N.217-03
Page 10
design considerations in accordance with 1997 UBC Section 1815. The design
procedures outlined in 1997 UBC Section 1815 are based on the thickness and
plasticity index of each different soil type existing within the upper 15 feet of the
building site. For final design purposes we have assumed an effective plasticity index
of 12 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 reducing 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 reduce post-construction movement
and/or cracking, they generally do not positively mitigate all potential adverse 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,
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 depths indicated in the 1997
UBC Table 18-I-C (i.e., 12 inches for one-story and 18 inches or greater for two-
story construction). Interior continuous footings for both one- and two-story
construction may be founded at a depth of 12 inches or more below top of slab.
Continuous footings should have a width of 12 and 15 inches or greater, 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 24 inches
square or greater and founded at a depth of 18 inches or more below the lowest
adjacent final grade. The pad footings should be reinforced in accordance with
the structural engineer's recommendations.
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RICHMOND AMERICAN HOMES
TR 26828-1 Lots 26-30/Temecula
September 18, 2003
J.N. 217-03
Page II
. Floor Slabs
- Unless a more stringent design is recommended by the architect or the structural
engineer, we recommend a slab thickoess of 4 inches or greater for both living-
area and garage-floor slabs and reinforcing consisting of either 6x6- W2.9xW2.9
WWF welded-wire mesh or No.3 bars spaced a maximum of 18 inches on-
centers, both ways. Slab reinforcement should be supported on concrete chairs
or bricks so that the desired location near mid-height is achieved.
- Living-area concrete-floor slabs should be underlain with a moisture-vapor
retarder consisting of 10-mil polyethylene membrane or equivalent. Laps within
the membrane should be sealed and 2 inches or more of clean sand be placed
over the membrane to promote uniform curing of the concrete.
- Garage-floor slabs should be placed separately from adjacent wall footings with
a positive separation maintained with 3/8-inch, 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 two No.4 bars, one top
and one bottom.
- Prior to placing concrete, the sub grade soils below living-area and garage-floor
slabs should be pre-watered to achieve a moisture content that is equal to or
slightly greater than optimum-moisture content. This moisture content should
penetrate to 12 inches or more into the subgrade soils.
POST-TENSIONED SLABS
In lieu of the preceding recommendations for conventional footings and floor slabs,
post-tensioned slabs maybe used. The actual design of post-tensioned slabs is referred
to the project structural engineer who is qualified in post-tensioned slab design, using
sound engineering practices. The post-tensioned slab-on-ground should be designed
in general conformance with the design specification os 1997 UBC Section 1816.
Alternate designs are allowed per 1997 UBC Section 1806.2 that addresses the effects
of expansive soils when present. However, to assist the structural engineer in his
design, the following parameters are recommended.
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RICHMOND AMERICAN HOMES
TR 26828-1 Lots 26-30/Temecula
September 18, 2003
J.N.217-03
Page 12
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Expansion Index -=---- Very Low
and Low
. ..... (0 to 50)
Assumed percent clay 30
Clay type Montmorillonite
Approximate depth of constant suction (feet) 7.0
Approximate soil suction (pF) 3.6
Approximate velocity or moisture flow (inches/month) 0.7
Thomwaite Index -20
Average edge Center lift 4.6
Moisture variation depth, t;n
(feet) Edge lift 2.2
Anticipated swell, Yon Center lift 14
(inches) Edl!e lift
0.4
. Perimeter footings for either one- or two-story dwellings may be founded at a depth
of 12 or more inches below the nearest adjacent final-ground surface. Interior
footings may be founded at a minimum depth of 12 inches below the top of the
finish-floor slab.
. Dwelling-area floor slabs constructed on-ground should be underlain with a
moisture-vapor retarder consisting of 10-mil thick polyethylene membrane. One
or more inch of clean sand should be placed over the membrane to promote
uniform curing of the concrete.
. Presaturation of sub grade soils below slabs-on-ground will not be required.
However, subgrade soils should be thoroughly moistened prior to placing concrete.
. The design modulus of subgrade reaction (k) should be 300 tons per cubic foot.
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 1997 UBC Sections 1626 through l633. The
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RICHMOND AMERICAN HOMES
TR 26828-1 Lots 26-30/Temecula
September 18, 2003
J.N.217-03
Page 13
method of design is dependent on the seismic zoning, site characteristics, occupancy
category, building configuration, type of structural system and on the building height.
For structural design in accordance with the 1997 UBC, a computer program
developed by Thomas F. Blake (UBCSEIS, 1998/1999) was utilized which compiles
fault 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 Band
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 the computer generated data using UBCSEIS, the Elsinore-Julian (Type A)
segment of the Elsinore fault zone, located approximately 12.1 kilometers from the
site, could generate severe site ground motions with an anticipated maximum moment
magnitude of 7.1 and anticipated slip rate of 5.0 mm/year. However, the closest
Type B fault which is the Elsinore-Temecula fault located 1.3 kilometers to the
southwest of Tract 23066-3 would probably generate the most severe site ground
motions with an anticipated maximum moment magnitude of 6.8 and anticipated slip
rate of 5.0 mmlyear. Based on our evaluation using UBCSEIS, the following 1997
UBC seismic design coefficients are recommended for the proposed residential
structures. These criteria are based on the soil profile type as determined by existing
subsurface geologic conditions, on the proximity of the Elsinore- Temecula fault and
on the maximum moment magnitude and slip rate.
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RICHMOND AMERICAN HOMES
TR 26828-1 Lots 26-30/Temecula
September 18, 2003
J.N.217-03
Page 14
I 1997 UBC TABLE I FACTOR I
Figure 16-2 Seismic Zone 4
16-1 Seismic Zone Factor Z 0.4
l6-U Seismic Source Type B
l6-J Soil Profile Type SD
16-S Near-Source Factor Na 1.0
l6-T Near-Source Factor Nv 1.2
l6-Q Seismic Coefficient en 0.44 N, = 0.45*
l6-R Seismic Coefficient C 0.64 N" ~ 0.78*
* Note - Calculations performed by the computer program UBCESEIS. Calculated results may vary
due to interpolated distances utilized by the program.
SOIL CHEMISTRY
Laboratory test results indicate onsite soils contain negligible soluble-sulfate contents.
As such, concrete in contact with soil may utilize Type I or II Portland cement. The
laboratory test data for chloride concentration, resistivity and pH indicate onsite soils
may be moderately corrosive to buried steel in direct contact with onsite soils.
MASONRY BLOCK WALLS
Construction on or Near the Tops of Descending Slopes
Continuous footings for masonry block walls proposed on or within 5 feet from the top
of a descending slope should be deepened such that a horizontal clearance of 5 or more
feet is maintained between the outside bottom edge of the footing and the slope face.
The footings should be reinforced with two No.4 bars, one top and one bottom and as
recommended by the structural engineer. Plans for any top-of-slope block walls
proposmg pIer and grade-beam footings should be reviewed by Petra prior to
construction.
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RICHMOND AMERICAN HOMES
TR 26828-1 Lots 26-30/Temecula
September 18, 2003
J.N.217-03
Page 15
Construction on Level Ground
Where masonry block walls are proposed on level ground and at least 5 feet from the
tops of descending slopes, the footings for these walls may be founded at a minimum
depth of 12 or more 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
and as recommended by the structural engineer.
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.
CONCRETEFLATWORK
Thickness and Joint Spacing
To reduce the potential of unsightly cracking, concrete sidewalks and patio-type slabs
should be 4 or more inches thick and provided with construction or expansion joints
every 6 feet or less. Concrete-driveway slabs should be 4 or more inches thick and
provided with construction or expansion joints every 10 feet or less.
Subgrade Preparation
As a further measure to reduce cracking of concrete fIatwork, the sub grade soils below
concrete-fIatwork areas should first be compacted to a relative density of90 or more
percent and then thoroughly wetted to achieve a moisture content that is equal to or
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RICHMOND AMERICAN HOMES
TR 26828-1 Lots 26-30/Temecula
September 18,2003
J.N.217-03
Page 16
slightly greater than optimum moisture content. This moisture should extend to a depth
of 12 or more inches below subgrade and maintained in the soils during placement of
concrete. Pre-watering of the soils will promote unifonn curing of the concrete and
reduce the development of shrinkage cracks. A representative of the project soils
engineer should observe and document 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 reduce
infiltration of water into the adjacentfoundation soils. The surface of the ground in
these areas should also be sloped at a gradient of 2 or more percent away from the
walls and foundations. Drip-irrigation systems are also recommended to reduce the
likelihood of overwatering and subsequent saturation of the adjacent foundation soils.
UTILITY TRENCHES
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 relative density of 90 or more 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 document proper compaction.
For deep trenches with vertical walls, backfill should be placed in approximately 1- 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
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RICHMOND AMERICAN HOMES
TR 26828-1 Lots 26-30/Temecula
September 18, 2003
J.N.217-03
Page 17
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.
To avoid point-loads and subsequent distress to clay, cement or plastic pipe, imported
sand bedding should be placed I or more foot above pipes in areas where excavated
trench materials contain significant cobbles. Sand-bedding materials should be
compacted and tested.
Where utility trenches are proposed parallel to building footings (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.
SLOPE LANDSCAPING AND MAINTENANCE
The engineered slopes within the subject lots are considered grossly and surficially
stable and are expected to remain so under normal conditions provided the slopes are
landscaped and maintained thereafter in accordance with the following
recommendations.
. Compacted-earth berms should be constructed along the tops of the engineered fill
slopes to reduce the likelihood water from flowing directly onto the slope surfaces.
. The slopes should be landscaped as soon as practical when irrigation water is
available. The landscaping should consist of deep-rooted, drought-tolerant and
maintenance-free plant species. A landscape architect should be consulted to
determine the most suitable groundcover. Iflandscaping 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
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RICHMOND AMERICAN HOMES
TR 26828-1 Lots 26-30/Temecula
September 18, 2003
J.N.217-03
Page IS
should be avoided. On the other hand,
detrimental to slope performance.
allowing the soils to dry-out is also
. Irrigation systems should be constructed at the surface only. Construction of
sprinkler Jines in trenches is not recommended.
. During construction of terrace drains, downdrains or earth berms, care must be
taken to avoid placement ofloose 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 ofleaking
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.
. Property owners should be advised of the potential problems tllat can develop when
drainage on the building pads and adjacent slopes is altered. Drainage can be
altered due to the placement of fill and construction of garden walls, retaining
walls, walkways, patios, swimming pools, spas and planters.
POST-GRADING OBSERV A nONS AND TESTING
Petra should be notified at the appropriate times in order that we may provide the
following observation and testing services during the various phases of post grading
construction.
. Building Construction
Observe footing trenches when first excavated to document adequate depth and
competent soil-bearing conditions.
- Re-observe footing trenches, if necessary, if trenches are found to be excavated
to inadequate depth and/or found to contain significant slough, saturated or
compressible soils.
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RICHMOND AMERICAN HOMES
TR 26828-1 Lots 26-30/Temecula
September 18, 2003
J.N.217-03
Page 19
Observe pre-soaking of subgrade soils below living-area and garage floor slabs
to document moisture content and penetration.
. Masonry Block-Wall Construction
- Observe footing trenches when first excavated to document adequate depth and
competent soil-bearing conditions.
- Re-observe footing trenches, if necessary, if trenches are found. to be excavated
to inadequate depth and/or found to contain significant slough, saturated or
compressible soils.
. Exterior Concrete-Flatwork Construction
- Observe and test subgrade soils below all concrete- flatwork areas to document
adequate compaction and moisture content.
. Utility-Trench Backfill
Observe and test placement of all utility-trench backfill to document adequate
compaction.
. Re-Grading
Observe and test placement of fill to be placed above or beyond the grades
shown on the approved grading plans.
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RICHMOND AMERICAN HOMES
TR 26828-1 Lots 26-30/Temecula
September 18,2003
J.N.217-03
Page 20
This opportunity to be of service is sincerely appreciated. If you have any questions,
please contact this office.
Respectfully submitted,
PETRA GEOTECHNICAL
~
Robert L. Gregorek II, CEG
Senior Associate Geologist
CEG 1247
Attachments:
Distribution: (1) Addressee
(5) Richmond American Homes - Field Office
Attention: Mr. Bob Bechtold
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EXPLANATION
Scale
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I I
(HORIZONTAL & VERTICAL)
GEOLOGIC CROSS SECTIONS
A-A' AND 8-8'
e PETRA GEOTECHNICAL. INC.
IN 217-03 SEPT. 2003
FIGURE 2
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ARTIFICIAL FILL
ARTIFICIAL FILL. COMPACTED
QUATERNARY ALLUVIUM
PAUBA FORMATION BEDROCK
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I TABLE II
I Field Density Test Results
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I 08/11/03 127 Lot 30 1142.0 10.2 125.0 97 129.0 2
08/11/03 131 Lot 29 1144.0 9.5 122.0 95 129.0 2
08/12/03 133 Lot 30 1155.0 lOA 118.2 92 129.0 2
I 08/12/03 138 Lot 29 1145.0 11.1 116.9 91 129.0 2
08113/03 194 Lot 30 1154.0 19.5 105.1 92 114.5 3
I 08/13/03 196 Lot 29 1154.0 12.6 113.2 95 119.5 10
08/14/03 200 Lot 27 1154.0 11.1 114.9 96 119.5 10
08/14/03 204 Lot 29 1157.0 8.1 121.9 94 130.0 6
I 08/14/03 205 Lot 28 1155.0 7.8 114.3 96 119.5 10
08/15/03 209 Lot 30 1157.0 7.3 116.8 90 130.0 6
08/15/03 210 Lot 28 1157.0 9.3 117.8 91 130.0 6
I 08/15/03 212 Lot 26 1156.0 8A 108.7 91 119.5 10
08/15103 214 Lot 27 1157.0 lOA 114.6 93 123.0 8
08/18/03 216 Lot 27 1159.0 14.0 116.9 90 130.0 6
I 08/18/03 217 Lot 30 1160.0 13.6 110.8 93 119.5 10
08/18/03 219 Lot 29 1160.0 8.6 117.3 90 130.0 6
I 08/18/03 220 Lot 28 1159.0 7.8 121.3 93 130.0 6
08/18/03 221 Lot 26 1169.0 10.6 119.0 92 130.0 6
08/19/03 225 Lot 27 1164.0 9.7 123.0 95 130.0 6
I 08/19/03 226 Lot 26 1167.0 10.7 117.2 90 130.0 6
08/19/03 228 Lot 26 1171.0 9.5 118.5 91 130.0 6
08/26/03 290A Lot 26 FG 9.0 106.5 93 114.5 3
I 08/26/03 291 Lot 27 FG 8.0 113.5 88 129.0 2
08/26/03 292 Lot 28 FG 7.9 124.7 97 129.0 2
08/26/03 293 Lot 29 FG 7.0 116.6 90 129.0 2
I 08/26/03 294 Lot 30 FG 6.6 115.9 90 129.0 2
09/04/03 378 Lot 26 finish slope 1165.0 11.7 112.6 92 123.0 8
09/04/03 379 Lot 27 finish slope 1163.0 9.9 1/1.9 91 123.0 8
I 09/04/03 380 Lot 28 finish slope 1160.0 9.8 113.5 92 123.0 8
09/04/03 381 Lot 29 finish slope 1160.0 9.3 113A 91 125.0 9
I 09/04/03 382 Lot 30 finish slope 1161.0 9.5 113.9 93 123.0 8
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PETRA GEOTECHNICAL, INC. TR 26828-1/Lots 26-30 SEPTEMBER 2003
I J.N.217-03 *Sandcone TABLE T-1I1
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REFERENCES
International Conference of Building Officials, 1997, Uniform Building Code, Volume 2, Structural Engineering
Design Provisions, dated April.
, 1998, Maps of Known Active Fault Near-Source Zones in California and Adjacent Portion of Nevada,
February.
Petra Geoteclmical, Inc., 2003, Supplemental Geoteclmical Investigation, Tracts 26828, 26828-1 and 26828-2, City
of Temecula, Riverside County, California, J.N. 377-02, dated June 25.
PETRA GEOTECHNICAL, INC.
J.N. 217-03
SEPTEMBER 2003
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APPENDIX A
LABORATORY TEST CRITERIA
LABORATORY TEST DATA
o PETRA
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APPENDIX A
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LABORATORY TEST CRITERIA
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! Laboraton Maximum Drv Densitv
Maximum dry density and optimum moisture content were determined for selected samples of soil and bedrock
materials in accordance with ASTM Test Method D1557. Pertinent test values are given on Plate A-I.
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I Exnansion Index
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: Expansion index tests were performed on selected samples of soil and bedrock materials in accordance with ASTM
Test Method D4829. Expansion potential classifications were determined from 1997 UBC Table 18-I-B on the basis
of the expansion index values. Test results and expansion potentials are presented on Plate A-I.
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, Corrosion Tests
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Chemical analyses were performed on selected samples of onsite soil to determine concentrations of soluble sulfate
and chloride, as well as pH and resistivity. These tests were performed in accordance with California Test Method
'Nos. 417 (sulfate), 422 (chloride) and 643 (pH and resistivity). Test results are included on Plate A-I.
, Soluble Sulfate
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Chemical analysis was performed on a selected samples of onsite soil to determine concentrations of soluble sulfate.
This test was performed in accordance with California Test Method No. 417. The test results are included on
,Plate A-I.
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Atterber~ Limits
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Atterberg limit tests (Liquid Limit and Plastic Index) were performed on selected samples to verify visual
classifications. These tests were performed in accordance with ASTM Test Method D4318. Test results are
i presented on Plate A-2.
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PETRA GEOTECHNICAL, INC.
J.N.217-03
SEPTEMBER 2003
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LABORATORY MAXIMUM DRY DENSITY'
2 Silty SAND 8.0 ]29.0
3 Gravelly SAND 10.0 114.5
6 Clayey SAND 10.0 130.0
8 Silty SAND 12.0 123.0
9 Silty SAND 10.5 125.0
10 Silty SAND 12.5 119.5
11 Silt SAND with fine Gravel ]2.5 122.5
EXPANSION INDEX TEST DATA
26
27
29
30
26
18 Very Low
34 Low
27 and 28
29
44 Low
30
36 Low
CORROSION TESTS
26 through 28
0.0081
135
7.2 2,100 concrete: negligible
steel: moderate
6.9 1,400 concrete: negligible
steel: hi h
29 through 30
0.004
140
(1) PER ASTM D1557
(2) PER ASTM D4829
(3) PER 1997 UBC TABLE 18-I-B
(4) PER CALIFORNIA TEST METHOD NO. 417
(5) PER CALIFORNIA TEST METHOD NO. 422
(6) PER CALIFORNIA TEST METHOD NO. 643
(7) PER CALIFORNIA TEST METHOD NO. 643
PETRA GEOTECHNICAL, INC.
J.N.217-03
SEPTEMBER 2003
PLATfA-l
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ATTERBERG LIMITS'
* Classification of [me portion of sample
(8) PER ASTM 04318
PETRA GEOTECHNICAL, INC.
J.N.217-03
SEPTEMBER 2003
PLA TE A-2
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