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Home My WebLink AboutSUP 07-03; South Coast Materials Quarry; Geotechnical Investigation; 2011-03-04GEOCON INC OBPORATBD GEOTECHNICAL • EN V_L-E..-Q..-bl M--E--N Project No. 07135-42-01 March 4, 2011 RECORD COPY .___ Initiai L • MATERIALS Hanson Aggregates Pacific Southwest, Inc. Post Office Box 639069 San Diego, California 92163-9069 Attention: Mr. William Berger JUN202Q11 ENGINEERING DEPARTMENT Subject: QUARRY CREEK CARLSBAD, CALIFORNIA 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. Grading and Erosion Control Plans for, Hanson Aggregates Quarry, prepared by Chang Consultants, dated February 28, 2011 (Bid Set). Dear Mr. Berger: In accordance with the request of Chang Consultants, Geocon Incorporated has prepared this letter providing 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 full flood conditions (i.e, water surface to within 3 feet of top of levee). We also are providing information relative to settlement of the embankment fill. 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. The results of the seepage analysis were then inputted into SLOPEW (Geoslope International, 2004), a two dimensional slope stability program that uses conventional limit equilibrium equations to determine factors of safety. We used direct shear strength parameters determined from laboratory testing in the stability analysis. The attached figure summarizes graphically the results of the slope stability analysis at full flood conditions. Our analysis indicates the proposed levee has a factor of safety in excess of 1.5 under flood conditions when the phreatic water surface is fully developed through the levee embankment. UHflI ^ CQ ID CO DC 6960 Flanders Drive • San Diego, California 92121-2974 • Telephone 858.558.6900 • Fax 858,558.6159 ••««• With respect to loss of freeboard as a result of levee settlement, it is our opinion embankment settlement will be minor. As previously indicated, all undocumented fill and compressible deposits will be removed from beneath the embankment fill. The embankment foundation will consist of Jurassic-aged Salto Intrusive bedrock. Settlement of the embankment foundation should not occur. Based on our experience with compacted fill soils, we estimate settlement magnitudes of up to 0.4 percent of the fill height could occur under self weight compression and hydroconsolidation. Based on the referenced grading plan and information contained in Reference 1, the levee embankment fill height will be approximately 40 feet at its maximum height, decreasing to 30 feet or less at the levee crest. Using an estimate of 0.4 percent of the fill height, we expect settlement to be approximately 2 inches or less. If you have any questions regarding this report, or if we may be of further service, please contact the undersigned at your convenience. Very truly yours, GEOCON INCORPORATED I, ~ . Rodney y. Mikesell GE2 RCM:dmc Attachment (2) Addressee (1) Chang Consultants Attention: Mr. Wayne Chang Project No. 07135-42-01 - 2 -March 4, 201 1 i> i .gsz Date: 3/3/2011 1.646 o Iat UJ Description: Compacted FillWt: 130 Cohesion: 300 120 140 160 180 200 Distance, ft