HomeMy WebLinkAboutLot 130 Geotechnical Investigation0
C
1 PETRA
COSTA MESA • SAN DIEGO • PALMDALE
Rivers -
Cpuf & palet
' BuildlnS
19�7�
OCT 2
R.H. ACQUISITION
' 355 N. Lantana St., Ste. 670
Camarillo, CA 93010
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Attention: Mr. Steve Ford
September 23, 1996
J.N. 298-87
Subject: Geotechnical Review of Rough Grading Plans, Tract No. 23064-2,
County of Riverside, California.
References: See attached list.
Gentlemen:
In response to a 'Plan Check Corrections" list prepared by the County of
Riverside Department of Building and Safety, Grading Division, our firm has
reviewed the rough grading plans for Tract No. 23064-2 prepared by Ranpac
Engineering Corporation (plans dated 5-21-90). The purpose of this review was
to evaluate the geotechnical aspects of the proposed grading, including the
stability of planned cut and fill slopes. The county reviewer has also requested
copies of Reference Nos. 2 and 5. Therefore, we are forwarding copies of these
to the County.
PROPOSED GRADING
Mass cut and fill grading is proposed within Tract No. 23064-2 to develop 129
residential lots and associated access streets and slopes. A park site will also
be mass graded (Lot 130) and temporary cut slopes are planned around the a
school site (Lot 131), Maximum planned vertical depths of cut and fill below
and above existing grades are approximately 85 feet and 45 feet, respectively.
However, following removal of low density alluvial materials in canyon areas and
PETRA GEOTECHNICAL INC.
3185-A Alway Avenue
'
Co,la Mesa, CA 92626
Te1:(714)549-8921
Fax: (714) 549-1438
Attention: Mr. Steve Ford
September 23, 1996
J.N. 298-87
Subject: Geotechnical Review of Rough Grading Plans, Tract No. 23064-2,
County of Riverside, California.
References: See attached list.
Gentlemen:
In response to a 'Plan Check Corrections" list prepared by the County of
Riverside Department of Building and Safety, Grading Division, our firm has
reviewed the rough grading plans for Tract No. 23064-2 prepared by Ranpac
Engineering Corporation (plans dated 5-21-90). The purpose of this review was
to evaluate the geotechnical aspects of the proposed grading, including the
stability of planned cut and fill slopes. The county reviewer has also requested
copies of Reference Nos. 2 and 5. Therefore, we are forwarding copies of these
to the County.
PROPOSED GRADING
Mass cut and fill grading is proposed within Tract No. 23064-2 to develop 129
residential lots and associated access streets and slopes. A park site will also
be mass graded (Lot 130) and temporary cut slopes are planned around the a
school site (Lot 131), Maximum planned vertical depths of cut and fill below
and above existing grades are approximately 85 feet and 45 feet, respectively.
However, following removal of low density alluvial materials in canyon areas and
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R.H. ACQUISITION
September 23, 1996
J.N. 298-87
Page 2
tributary drainages, the resultant maximum depth of compacted fill will be
approximately 55 to 60 feet. Canyon subdrains are planned along the axes of
the major canyons and tributary drainages following removal of low density
alluvial materials.
Cut and fill slopes are planned at a maximum ratio of 2:1 (horizontal to vertical).
The maximum proposed cut slope height is approximately 75 feet and the
maximum proposed fill slope height is approximately 45 feet. Mid -slope terrace
drains are proposed on all graded slopes exceeding a height of 30 feet.
SUBSURFACE SOIL AND BEDROCK CONDITIONS
The subject tract is underlain by late Pleistocene sedimentary bedrock materials
belonging to the Pauba Formation. In major canyon areas and tributary
drainages, the Pauba Formation is overlain with low density surficial deposits
of recent alluvium, colluvium and/or slopewash. In the topographically higher
areas, the Pauba Formation is mantled with a relatively thin layer of weathered
bedrock (residual soil). A detailed description of the above materials is provided
in Reference No. 5.
GRADING RECOMMENDATIONS
The 'Earthwork" recommendations presented in Reference No. 5 remain
applicable for the site; however, structural fills have already been placed in
several areas along the edges of the adjacent golf course fairways. These
compacted fills were placed under the purview of this firm in accordance with
the recommendations presented in Reference No. 2.
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R.H. ACQUISITION
September 23, 1996
J.N. 298-87
Page 3
SLOPE STABILITY CALCULATIONS
Slope stability calculations have been performed for the proposed 2:1 cut and
fill slopes for their respective maximum planned heights (75 feet and 50 feet).
Shear strength parameters for compacted fill and Pauba Formation bedrock
materials are based on laboratory test data presented in Reference No. 5. The
weakest shear strength values determined for remolded soils and in situ bedrock
were used in the calculations. A summary of these values is presented below:
' 1. Compacted Fill
Angle of internal friction = 34°
' Cohesion = 100 psf
Saturated unit weight = 120 pcf
' 2. In Situ Bedrock
Angle of internal friction = 36°
' Cohesion = 590 psf
Saturated unit weight = 120 pcf
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Under static loading conditions, factors of safety exceeding 1.5 were determined
for both cut and fill slopes. A fault hazard area has been defined along the
westerly tract boundary. Therefore, a horizontal seismic coefficient of 0.2g was
used in the calculations to evaluate pseudo -dynamic loading conditions. These
calculations resulted in factors of safety exceeding 1.1 for both cut and fill slopes.
The calculations are attached to this report.
CONCLUSIONS AND RECOMMENDATIONS
Grading Plan Review
Based on our review of the grading plans, the plans were found to have been
prepared in accordance with our recommendations presented in Reference No.
5 and are considered acceptable from a geotechnical point of view.
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R.H. ACQUISITION
Cut and Fill Slope Stability
September 23, 1996
J.N. 298-87
Page 4
Cut slopes will expose Pauba Formation bedrock materials consisting of dense
to locally very dense, massive, fine to coarse-grained sandstone and silty sand-
stone with occasional gravel and silt beds. Structurally, the bedrock is generally
void of significant adverse bedding. Therefore, based on the structure of the
bedrock and stability calculations, all cut slopes are expected to be grossly stable;
however, as noted in Reference No. 5, all cut slopes should be observed by the
project engineering geologist to confirm favorable geologic conditions.
Based on stability calculations, all fill slopes are expected to be grossly stable
provided they are constructed in accordance with the recommendations presented
in Reference No. 5.
All cut and fill slopes are also expected to be surficially stable and to remain
so under normal conditions, and provided they are landscaped and maintained
thereafter in accordance with the recommendations presented in Reference No.
5.
Evaluation of Soil/Bedrock Expansion Potential and Plasticity Index
Onsite soil and bedrock materials exhibit expansion potentials varying from
VERY LOW to MEDIUM. Therefore, as recommended in Reference No. 5,
expansive soil and bedrock conditions will have to evaluated on a lot by lot basis
during and at the completion of rough grading.
In addition to evaluating expansive soil and bedrock conditions, Section 1803.2
of the 1994 U.B.C. specifies that special design considerations (conforming to
Section 1815) are required for soils with an expansion index greater than 20
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R.H. ACQUISITION
September 23, 1996
J.N. 298-87
Page 5
' (LOW expansion potential and greater). The special design considerations are i
based on the effective plasticity index for the upper 15 feet of the soil layers
' underlying the building sites. Therefore, determination of the plasticity index
for soils with an expansion index greater than 20 located in the upper 15 feet
of the building sites will also be required during grading.
We trust the comments and recommendations presented herein adequately
address the information requested by the reviewer for the County of Riverside.
Should you have any questions, please do not hesitate to call.
Respectfully submitted,
PETRA GEOTECHNICAL, INC.
Allen Bell
President
Engineering Geologist
CEG 936
CB/AB/SJ/jtd
=: 19861200/28 7kFEV
Siamak Jafro i, PhD
Principal En ` eer
GE 2024
No. GE 002024
EXP. GM/00
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1. Evaluation of Faulting and Liquefaction Potential, Portion of Wolf Valley Project,
Rancho California, County of Riverside, California; report by Earth Research Associates,
Inc., dated November 20, 1987.
2. Removal Requirements for Structural Fills Adjacent to Golf Course Fairway Numbers
1, 2, 3, 4, 8 and 18, Redhawk Project, Rancho California, County of Riverside, Califor-
nia; report by Earth Research Associates, Inc., dated January 18, 1988.
' 3. Preliminary Soils Engineering and Engineering Geologic Investigation, Redhawk Project,
Rancho California, County of Riverside, California; report by Earth Research Associates,
Inc., dated February 2, 1988.
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4. Supplemental Evaluation of Faulting, Southwest Portion of Redhawk Project, Rancho
California Area, County of Riverside, California; report by Petra Geotechnical, Inc.,
dated March 1, 1989.
05�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; report by Petra Geotechnical, Inc.,
dated May 8, 1989.
PETRA GEOTECHNICAL, INC.
J.N. 298-87
Fl
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STABL6H •*
by
Purdue University
--Slope Stability Analysis --
Simplified Janbu, Simplified Bishop
or Spencer's Method of Slices
Run Date: 09-20-96
Time of Run: 4:58pm
Run By: Petra Geotechnical, Inc.
Input Data Filename: D:FILL-3.IN
Output Filename: D:FILL-3.0UT
Plotted Output Filename: D:FILL-3.PLT
PROBLEM DESCRIPTION Tract 23064-2: Static stability analysis
of 50 -foot high fill slope
BOUNDARY COORDINATES
5 Top Boundaries
5 Total Boundaries
Boundary X -Left
No. (ft)
1 .00
2 20.00
3 70.00
4 76.00
5 126.00
Y -Left
X -Right
Y -Right
Soil Type
(ft)
(ft)
(ft)
Below Bnd
25.00
20.00
25.00
1
25.00
70.00
50.00
1
50.00
76.00
50.00
1
50.00
126.00
75.00
1
75.00
200.00
75.00
1
ISOTROPIC SOIL PARAMETERS
1 Type(s) of Soil
Soil Total Saturated Cohesion Friction Pore Pressure Piez.
Type Unit Wt. Unit Wt. Intercept Angle Pressure Constant Surface
No. (pcf) (pcf) (psf) (deg) Param. (psf) No.
1 120.0 120.0 100.0 34.0 .00 .0 0
A Critical Failure Surface Searching Method, Using A Random
Technique For Generating Circular Surfaces, Has Been Specified.
200 Trial Surfaces Have Been Generated.
10 Surfaces Initiate From Each Of 20 Points Equally Spaced
Along The Ground Surface Between X - 15.00 ft.
and X - 25.00 ft.
Each Surface Terminates Between X - 130.00 ft.
and X - 180.00 ft.
Unless Further Limitations Were Imposed, The Minimum Elevation
At Which A Surface Extends Is Y - .00 ft.
10.00 ft. Line Segments Define Each Trial Failure Surface.
Plate A-1
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• • Safety Factors Are Calculated By The Modified Bishop Method
Failure Surface Specified By 15 Coordinate Points
Point X -Surf Y -Surf
No. (ft) (ft)
1 22.90 26.45
2 32.85 27.43
3 42.74 28.88
4 52.56 30.80
5' 62.27 33.18
6 71.86 36.02
7 81.30 39.30
8 90.58 43.03
9 99.68 47.19
10 108.56 51.77
11 117.22 56.78
12 125.64 62.18
13 133.79 67.97
14 141.65 74.15
15 142.64 75.00
Circle Center At X = 7.1 ; Y 237.6 and Radius, 211.7
1.892 *.�
Plate A-2
Y -Axis
(ft)
1
Tract 23064-2: Static stability analysis of 50 -foot high fill slope
Ten Most Critical. C:FILL-3.PLT By: Petra Geotechnical 09-20-96 298-87 .
0 40 80 120 160 200
PCSTABL5M FSmin=1.89 X -Axis (ft)
Factors Of Safety Calculated By The Modified Bishop Method
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•• STABL6H ••
by
Purdue University
--Slope Stability Analysis --
Simplified Janbu, Simplified Bishop
or Spencer's Method of Slices
Run Date: 09-20-96
Time of Run: 4:56pm
Run By: Petra Geotechnical, Inc.
Input Data Filename: D:FILL-4.IN
Output Filename: D:FILL-4.OUT
Plotted Output Filename: D:FILL-4.PLT
PROBLEM DESCRIPTION Tr. 23064-2: Seismic stability analysis
of 50 -foot high fill slope
BOUNDARY COORDINATES
5 Top Boundaries
5 Total Boundaries
Boundary X -Left
No. (ft)
1 .00
2 20.00
3 70.00
4 76.00
5 126.00
Y -Left
X -Right
Y -Right
Soil Type
(ft)
(ft)
(ft)
Below Bnd
25.00
20.00
25.00
1
25.00
70.00
50.00
1
50.00
76.00
50.00
1
50.00
126.00
75.00
1
75.00
200.00
75.00
1
ISOTROPIC SOIL PARAMETERS
1 Type(s) of Soil
Soil Total Saturated Cohesion Friction Pore Pressure Piez.
Type Unit Wt. Unit Wt. Intercept Angle Pressure Constant Surface
No. (pcf) (pcf) (psf) (deg) Param. (psf) No.
1 120.0 120.0 100.0 34.0 .00 .0 0
A Horizontal Earthquake Loading Coefficient
Of .200 Has Been Assigned
A Vertical Earthquake Loading Coefficient
Of .000 Has Been Assigned
Cavitation Pressure = .0 psf
A Critical Failure Surface Searching Method, Using A Random
Technique For Generating Circular Surfaces, Has Been Specified.
200 Trial Surfaces Have Been Generated.
10 Surfaces Initiate From Each Of 20 Points Equally Spaced
Along The Ground Surface Between X - 15.00 ft.
and X - 25.00 ft.
Plate A-4
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Each Surface Terminates Between X - 130.00 ft.
and X - 180.00 ft.
Unless Further Limitations Were Imposed, The Minimum Elevation
At 'Which A Surface Extends Is Y = .00 ft.
10.00 ft. Line Segments Define Each Trial Failure Surface.
• • Safety Factors Are Calculated By The Modified Bishop Method + +
Failure Surface Specified By 15 Coordinate Points
Point X -Surf Y -Surf
No. (ft) (ft)
1 22.90 26.45
2 32.85 27.43
3 42.74 28.88
4 52.56 30.80
5 62.27 33.18
6 71.86 36.02
7 01.30 39.30
8 90.58 43.03
9 99.68 47.19
10 108.56 51.77
11 117.22 56.78
12 125.64 62.18
13 133.79 67.97
14 141.65 74.15
15 142.64 75.00
Circle Center At X 7.1 ; Y 237.6 and Radius, 211.7
*•+ 1.203 +++
Plate A-5
A
Y -Axis
(ft)
Tr. 23064-2: Seismic stability analysis of 50 -foot high fill slope
Ten Most Critical. C:FILL-4.PLT By: Petra Geotechnical 09-20-96 298-87
40 80 120 160
PCSTABL5M FSmin=1.20 X -Axis Pt)
Factors Of Safety Calculated By The Modifad Bishop Method
200
# FS
a 1.20
b 1.20
21
Label
Fill
Soil Total
T�yype Unit Mt.
No. ( cf)
1 P120
Saturated Cohesion
Unit Mt. Intercept
( cf) ( sf)
1p20 R00
Friction
Angle
(de )
3�
Pore
Pressure
Param.
0
Pressure Piez.
Constant Surface
(psf) No.
0
a 1.24
e 1.24
f 1.25
0 1.25
h 1.25
1 1.25
) 1.28
40 80 120 160
PCSTABL5M FSmin=1.20 X -Axis Pt)
Factors Of Safety Calculated By The Modifad Bishop Method
200
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�* STABL6H
by
Purdue University
--Slope Stability Analysis --
Simplified Janbu, Simplified Bishop
or Spencers Method of Slices
Run Date: 09-20-96
Time of Run: 5:07pm
Run By: Petra Geotechnical, Inc.
Input Data Filename: D:CUT-3.IN
Output Filename: D:CUT-3.OUT
Plotted Output Filename: D:CUT-3.PLT
PROBLEM DESCRIPTION Tract 23064-2: Static stability analysis
of 75 -foot high cut slope
BOUNDARY COORDINATES
5 Top Boundaries
5 Total Boundaries
Boundary X -Left
No. (ft)
1 .00
2 25.00
3 95.00
4 101.00
5 181.00
Y -Left
x -Right
Y -Right
Soil Type
(ft)
(ft)
(ft)
Below End
25.00
25.00
25.00
1
25.00
95.00
60.00
1
60.00
101.00
60.00
1
60.00
181.00
100.00
1
100.00
240.00
100.00
1
ISOTROPIC SOIL PARAMETERS
1 Type(s) of Soil
Soil Total Saturated Cohesion Friction Pore Pressure Piez.
Type Unit Wt. Unit Wt. Intercept Angle Pressure Constant Surface
No. (pcf) (pcf) (psf) (deg) Param. (psf) No.
1 120.0 120.0 590.0 36.0 .00 .0 0
A Critical Failure Surface Searching Method, Using A Random
Technique For Generating Circular Surfaces, Has Been Specified.
200 Trial Surfaces Have Been Generated.
10 Surfaces Initiate From Each Of 20 Points Equally Spaced
Along The Ground Surface Between X - 20.00 ft.
and X - 30.00 ft.
Each Surface Terminates Between x - 190.00 ft.
and X - 230.00 ft.
Unless Further Limitations Were Imposed, The Minimum Elevation
At Which A Surface Extends Is Y - .00 ft.
10.00 ft. Line Segments Define Each Trial Failure Surface.
Plate A-7
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• • Safety Factors Are Calculated By The Modified Bishop Method
Failure Surface Specified By 22 Coordinate Points
Point X -Surf Y -Surf
No. (ft) (ft)
1 22.63 25.00
2 32.59 24.06
3 42.58 23.64
4 52.58 23.73
5 62.56 24.34
6 72.50 25.46
7 82.36 27.09
8 92.13 29.23
9 101.78 31.87
10 111.28 35.00
11 120.60 38.62
12 129.72 42.71
13 138.62 47.26
14 147.28 52.27
15 155.66 57.72
16 163.76 63.60
17 171.54 69.88
18 178.99 76.55
19 186.08 83.60
20 192.80 91.01
21 199.13 98.75
22 200.05 100.00
Circle Center At X 45.8 ; Y = 217.7 and Radius, 194.1
•+• 2.508 •••
Plate A-8
Y -Axis
(ft)
Tract 23064-2: Static stability analysis of 75 -foot high cut slope
Ten Most Critical. C:CUT-3.PLT By: Petra Geotechnical 09-20-96 298-87
# FS
■2.51
Label
b 2.52
Bedrock
c 2.52
d 2.52
a 2.52
t 2.53
g 2.53
b 2.54
s 2.54
2.55
Soil Total Saturated Cohesion Friction Pore Pressure Piez.
Type Unit Mt. Unit Mt. Intercept Angle Pressure Constant Surface
o. (Pcf) (Pcf) (Psf) (deg) Parse. (pssf) No.
1 120 120 590 36
0 40 80 120 160 200
PCSTABL5M FSmin=2.51 X -Axis (ft)
Factors Of Safety Calculated By The Modified Bishop Method
240
•• STABL6H ••
by
Purdue University
--Slope Stability Analysis --
Simplified Sanbu, Simplified Bishop
or Spencer's Method of Slices
Run Date: 09-20-96
Time of Run: 5:08pm
Run By: Petra Geotechnical, Inc.
Input Data Filename: D:CUT-4.IN
Output Filename: D:CUT-4.OUT
Plotted Output Filename: D:CUT-4.PLT
PROBLEM DESCRIPTION Tr. 23064-2: Seismic stability analysis
of 75 -foot high cut slope
BOUNDARY COORDINATES
5 Top Boundaries
5 Total Boundaries
Boundary X -Left
No. (ft)
1 .00
2 25.00
3 95.00
4 101.00
5 181.00 _
Y -Left
X -Right
Y -Right
Soil Type
(ft)
(ft)
(ft)
Below Bnd
25.00
25.00
25.00
1
25.00
95.00
60.00
1
60.00
101.00
60.00
1
60.00
181.00
100.00
1
100.00
240.00
100.00
1
ISOTROPIC SOIL PARAMETERS
1 Type(s) of Soil
Soil Total Saturated Cohesion Friction Pore Pressure Piez.
Type Unit Wt. Unit Wt. Intercept Angle Pressure Constant Surface
No. (pcf) (pcf) (psf) (deg) Param. (psf) No.
1 120.0 120.0 590.0 36.0 .00 .0 0
A Horizontal Earthquake Loading Coefficient
Of .200 Has Been Assigned
A Vertical Earthquake Loading Coefficient
Of .000 Has Been Assigned
Cavitation Pressure = .0 psf
A Critical Failure Surface Searching Method, Using A Random
Technique For Generating Circular Surfaces, Has Been Specified.
200 Trial Surfaces Have Been Generated.
10 Surfaces Initiate From Each Of 20 Points Equally Spaced
Along The Ground Surface Between X - 20.00 ft.
and X - 30.00 ft.
Plate A-10
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1
1
1
Each Surface Terminates Between X - 190.00 ft.
and X - 230.00 ft.
Unless Further Limitations Were Imposed, The Minimum Elevation
At Which A Surface Extends Is Y = .00 ft.
10.00 ft. Line Segments Define Each Trial Failure Surface.
• • Safety Factors Are Calculated By The Modified Bishop Method +
Failure Surface Specified By 22 Coordinate Points
Point X -Surf Y -Surf
No. (ft) (ft)
1 22.63 25.00
2 32.59 24.06
3 42.58 23.64
4 52.58 23.73
5 62.56 24.34
6 72.50 25.46
7 82.36 27.09
8 92.13 29.23
9 101.78 31.87
10 111.28 35.00
11 120.60 38.62
12 129.72 42.71
13 138.62 47.26
14 147.28 52.27
15 155.66 57.72
16 163.76 63.60
17 171.54 69.88
18 178.99 76.55
19 186.08 83.60
20 192.80 91.01
21 199.13 98.75
22 200.05 100.00
Circle Center At X = 45.8 ; Y 217.7 and Radius, 194.1
*•* 1.649 •••
Plate A-11
WA
Tr. 23064-2: Seismic stability analysis of 75 -foot high cut slope
Ten Most Critical. C:CUT-4.PLT By: Petra Geotechnical 09-20-96 298-87
0 40 80 120 160 200 240
PCSTABL5M FSmin=1.65 X -Axis (ft)
Factors Of Safety Calculated By The Modified Bishop Method