HomeMy WebLinkAboutSUP 07-03; South Coast Materials Quarry; Geotechnical Investigation; 2011-03-23GEOCON
INC ORPORATED
GEOTECHNICAl
Project No. 07135-42-01
March 23,2011
ENVIRONMENTAL MATERIALS
RECORD COPY
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Initial
Hanson Aggregates Pacific Southwest, Inc.
Post Office Box 639069
San Diego, California 92163-9069
Attention: Mr. Marvin Howell
UN 2 02011
ENGINEERING
DEPARTMENT
Subject: QUARRY CREEK
CARLSBAD, CALIFORNIA
ADDITIONAL SLOPE STABILITY ANALYSIS FOR FEMA LEVEE
References: 1. Update Geotechnical Investigation, Amended Reclamation Plan, Quarry Creek
Refined Alternative 3, Carlsbad, California prepared by Geocon Incorporated
dated September 10, 2009 (Project No. 07135-42-01)
2. Slope Stability Analysis for FEMA Levee, Quarry Creek, Carlsbad, California,
prepared by Geocon Incorporated, dated March 4, 2011 (Project No. 07135-42-01).
3. Grading and Erosion Control Plans for, Hanson Aggregates Quarry, prepared by
Chang Consultants, dated February 28, 2011 (Bid Set).
Dear Mr. Howell:
In accordance with the request of Chang Consultants, Geocon Incorporated has prepared this letter
providing additional slope stability analyses for the FEMA Levee located at the east end of the
project site. Specifically, this letter addresses slope stability of the levee under varying loading
conditions including end of construction (Case I), sudden drawdown (Case II), critical flood stage
(Case III), steady seepage at flood stage (Case IV), and earthquake for Case I (Case VI). We also
evaluated uplift pressures at the embankment toe and seepage exit gradients.
The levee will be comprised of compacted fill overlying Jurassic-aged Salto Intrusive bedrock.
Undocumented fill will be removed from beneath the embankment during reclamation grading.
Current geologic conditions at the levee are shown on Cross Section D-D of Reference 1.
To evaluate seepage through the levee, we performed analysis using the computer program SEEPW
(Geoslope International, 2004) using the levee geometry shown on Reference 2. The cross section
analyzed is located along Cross Section D-D of Reference 1. SEEPW uses a finite element model to
establish boundary conditions based on geometry and permeability values to draw a flow net that can
be used to calculate flow rates and hydraulic gradients and to plot the phreatic water surface within
the embankment. Based on our analysis the maximum seepage exit gradient is 0.35. The seepage exit
gradient is sufficiently below 1.0 that piping should not occur. A plot of exit gradients is attached.
The results of the seepage analysis were inputted into SLOPEW (Geoslope International, 2004), a two
dimensional slope stability program that uses conventional limit equilibrium equations to determine
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6960 Flanders Drive • San Diego, California 92121-2974 • Telephone 858.558.6900 • Fax 858.558.6159
factors of safety. We used direct shear strength parameters determined from laboratory testing in the
stability analysis. The attached figures summarize graphically the results of the slope stability
analysis for the various loading conditions analyzed. Our analysis indicates the proposed levee has a
critical factor of safety in excess of the minimum required. Table I summarizes the factor of safety for
each loading condition.
If you have any questions regarding this letter, or if we may be of further service, please contact the
undersigned at your convenience.
Very truly yours,
GEOCON INCORPORATED
RCM:dmc
Attachments
(2) Addressee
(email) Chang Consultants
Attention: Mr. Wayne Chang
Project No. 07135-42-01 -2-March23,2011
TABLE I
SUMMARY OF SLOPE STABILITY ANALYSIS FOR FEMA LEVEE
Case
I
II
III
IV
VI
Loading Condition
End of Construction
Sudden Drawdown
Critical Flood Stage
Steady Seepage at Flood Stage
Earthquake (Case I)
Critical
Safety Factor
3.4
2.8
1.8
1.65
2.5
Minimum
Safety Factor Required
1.3
1.0
1.4
1.4
1.0
Project No. 07135-42-01 March 23, 2011
CASE I -3/21/2011
180 r—
160
140
120
O '
10°.g
UJ 80
60
40
20
Description: Compacted Fill
Wt: 130
Cohesion: 300
Phi: 30
Description: Compacted Fill
Wt: 130
Cohesion: 300
Phi: 30
',J .f' • Description: Bedroeik'
120 140 160 180 200 220 240 260 280 300 320 340 360 380
Distance, ft
400 420 440 460 480
CASE II - 3/21/2011
180 i—
160
140
120
4±c N-
| 10°
liLU
80
60
40
20
Description: Compacted Fill
Wt: 130
Cohesion: 300
Phi: 30
Description: Compacted Fill
Wt: 130
Cohesion: 300
Phi: 30
120 140 160 180 200 220 240 260 280 300 320
Distance, ft
340 360 380 400 420 440 460 480
o
1JD
LU
Quarry Creek (07135-42-01)
Section D-D
D-1 .gsz
Date: 3/3/2011
CASE III-3/21/2011
180 I—
160
140
Description: Compacted Fill
Wt: 130
Cohesion: 300
Phi: 30
Description: Compacted Fill
Wt: 130
Cohesion: 300
Phi: 30 .
Description: Bedrock
120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480
Distance, ft
Quarry Creek (07135^2-01)
Section D-D
D-1 .gsz
Date: 3/3/2011
CASE IV-3/21/2011
180
coto
uHI
160
140
120
100
80
20
Description: Compacted Fill
Wt: 130
Cohesion: 300
Phi: 30
Description: Compacted Fill
Wt: 130
Cohesion: 300
Phi: 30
caption: Bedrock
120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480
Distance, ft
CASE VI -3/22/2011
180
160
140
120
cg'+->ro
<v
LU
100
80
60
40
20
Description: Compacted Fill
Wt: 130
Cohesion: 300
Phi: 30
Description: Compacted Fill
Wt: 130
Cohesion: 300
Phi: 30
Despription: Bedrock' ^ \ -;' ;'
120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480
Distance, ft
Quarry Creek (07135-42-01)
Section D-D
D-1.gsz
Date: 3/3/2011
Pore Pressure Contours (ft)
180 i—
160 h-
ce
c"g*-^ro
JD
LLI
60 t=
40
20
120 140 160 180 200 220 240 260 280 300 320
Distance, ft
340 360 380 400 420 440 460 480
Quarry Creek (07135-42-01)
Section D-D
D-1.gsz
Date: 3/3/2011
Total Head Contours (ft)
180 i—
120 140 160 180 200 220 240 260 280 300 320
Distance, ft
340 360 380 400 420 440 460 480
0.35-1—
0.30-I
0.25-
0.20-
0.15-
y_«_
0.10
2OO 250 300 350 400