HomeMy WebLinkAboutTract Map 20703-2 Lots 9-10 Geotechnical Investigation
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. PETRA
COSTA MESA -AGOURA HILLS. SAN DIEGO. RANCHO CALIFORNIA. PALM DALE
April 28, 1992
J.N.202-92
BARRATI HOMES
2035 Corte del Nogal #160
Carlsbad, CA 92009
Attention: Mr. Tim Wellman
Subject: Geotechnical Report of Precise Grading, Model Site Build-Out,
Lots 9 and 10, Tract No. 20703-2, County of Riverside, California.
Gentlemen:
Submitted berewith is a su=ary of inspection and testing services provided by
tbis firm during regrading operations witbin tbe subject lots. Conclusions and
reco=endations relative to the suitability of tbe grading for the planned
development and foundation reco=endations for tbe proposed structures are
included berein.
REGULATORY COMPLIANCE
All processing of existing ground, removals, and placement of fill under tbe
purview of this report have been completed under tbe inspection of and with
selective testing by Petra Geotechnical, Inc. and are found to be in compliance
witb tbe Grading Code of tbe County of Riverside, California. The completed
work bas been reviewed and is considered adequate for tbe construction now
planned.
PETRA GEOTECHNICAl. lNG
3185-A Airway Avenue
Costa Mesa, CA 92626
Tel: (714) 549-8921
Fax. (714) 549-1438
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BARRATI HOMES
April 28, 1992
J.N. 202-92
Page 2
On tbe basis of our findings, tbe following reco=endations were prepared in
conformance witb generally accepted professional engineering practices, and no
furtber warranty is implied nor made.
PURPOSE OF GRADING
The purpose of tbe regrading operation was to remove a temporary model site
parking lot from Lots 9 and 10 and restore tbe pads to tbeir final grades for
construction of single-family residences.
SOILS ENGINEERING
Site Clearinl!
All aspbalt paving, curbs, gutters, buried pipe and landscape vegetation associat-
ed witb tbe temporary parking lot were removed from tbe site.
Preparation of Existinl! Ground
1. All saturated soil materials witbin landscaped areas were removed to
expose firm, competent soils.
2. Prior to placing fill, exposed surfaces in removal areas and remaining areas
where competent soils existed at grade were scarified to depths of 4 to 6
incbes, watered to acbieve near optimum moisture conditions, and recom-
pacted in place to a minimum relative compaction of 90 percent.
2-
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BARRATI HOMES
April 28, 1992
J.N. 202-92
Page 3
Fill Placement
1. Fill materials used to restore tbe pad to their final grades consisted of
onsite and imported soils baving the below mentioned soil classifications.
Fill materials were placed in approximately 4- to 6-inch maximum lifts,
watered or aerated as required to acbieve near optimum moisture condi-
tions, and were compacted to a minimum relative compaction of 90 per-
cent using a rubber-tired loader.
2. Maximum deptb of fill placed is approximately 2.5 feet on Lot 9.
Field Testinl!
1. Field density tests were performed using the Sand Cone Method (ASTM
D 1556), the Drive Cylinder Method (ASTM D 2937), and Nuclear Method
(ASTM D 2922 and D 3017). Test results are shown on Table I.
2. Field density tests were taken at vertical intervals of 6 to 12 inches as the
fills were being placed.
3. Visual classification of earth materials in the field was the basis for
determining wbich maximum density value to employ for a given density.
One-point checks were performed to supplement visual classification.
Laboratory Testinl!
1. Maximum Drv Density: The laboratory maximum dry density and optimum
moisture content for each major soil type were determined according to
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BARRATI HOMES
April 28, 1992
J.N. 202-92
Page 4
Test Method ASTM D 1557-78. The following table presents the pertinent
test values:
Soil
Type
Description
Optimum
Moisture (%)
A
B
Silty Clay
Silty Sand (Import)
22.0
9.0
Maximum Dry
Density (pet)
100
132
2. Expansion Potential: Expansion index tests were performed on samples
of subgrade soils witbin tbe lots in accordance with Uniform Building Code
Standard Test No. 29-2. Test results and expansion potentials per Table
29-C are as follows:
Lot No.
Expansion
Index
Expansion
Potential
9
10
109
101
High
Higb
3. Soluble Sulfates: A sample of near surface soils witbin the lots was
obtained for chemical analysis. The concentration of water soluble sulfates
was determined for tbis sample. The test result is presented below:
Lot No.
Sulfate (%)
10
0.120
Based on tbe above test results, near surface soils witbin the subject lots contain
greater tban 0.10 percent soluble sulfate content. Consequently, according to
Table 26-A-6 of the Uniform Building Code, Type V cement is reco=ended
for concrete construction on-grade.
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BARRATI HOMES
April 28, 1992
J.N. 202-92
Page 5
Foundation Desim
It has been brought to our attention that post-tensioned slabs and footings will
be used in the construction of tbe residences on Lots 9 and 10 in lieu of con-
ventional foundations. The use of post-tensioned slabs and footings is considered
feasible from a geotechnical point of view. However, tbe actual design is
referred to tbe project structural engineer who should consider the bigh expan-
sion potentials of the soils underlying the lots.
Other design reco=endations such as allowable bearing capacity and lateral
bearing are provided in detail in tbe previous reports for the project. These
reco=endations, as well as otbers pertaining to the geotechnical aspects of site
development, remain valid.
Foatinl! Inspections
All footing trenches should be inspected by the project soils engineer to verify
that they have been excavated into competent bearing soils. Tbis inspection
should be performed prior to placing reinforcing steel.
Utility Trench Backfill
1. All utility trench backfill should be compacted to a minimum relative com-
paction of 90 percent. The project soils engineer should verify proper com-
paction of all trench backfill.
2. Where exterior and interior utility trenches are proposed parallel to
building footings, the bottom of the trench should not extend below a 1: 1
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BARRATI HOMES
April 28, 1992
J.N. 202-92
Page 6
plane projected downward from the bottom edge of the adjacent footing.
Where this condition occurs, the adjacent footing should be deepened.
Additional Gradinl!
Our office should be notified at the appropriate times prior to any fill placement,
regrading of the lots, or backfilling of utility trenches so that we may verify
proper placement and adequate compaction.
Tbis report is subject to review by the controlling authorities for the project.
Respectfully submitted,
PETRA GEOTEq.INICALJNC.
~~.
Allen Bell
President
Engineering Geologist
CEG 936 .
/-- U~-~
Siamak Jafroudi, P~-
Principal Engineer
GE 2024
RM/AB/SJ/lb
CC: 1992\FHL\202-92
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I Date of
Test
I 4-21-92
4-22-92
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I 4-23-92
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J.N. 202-92
TABLE I
FIELD DENSITY TEST SUMMARY
Test Depth Moist. Unit Wt. % ReI. Soil
No. Location 1ft. ) (%) Lbs . ICu. Ft. Compo ~
1 Lot 9 1.5 39.0 81. 8 82* A
2 " 9 2.0 31.0 90.7 91 A
3 " 9 1.0 30.4 90.2 90 A
4 " 9 0.0 9.6 123.5 94 B
5 " 10 0.0 24.9 95.3 95 A
* Area overexcavated and replaced with compacted soil
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