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Interpretation of SGI Interface Shear Strength Test Results <br />Foothill Sanitary Landfill - Area 2A Liner System <br />SM10 <br />I <br />Sideslope Post -Peak Combination Strength Envelope <br />3 ti a- 5w6 <br />`,.v..tx S .. SCPe+�N� AAtdAA3r <br />--^°�•..... 4iCC5lPrR? f.;lfl?tkRx4i'R €� <br />AM i0ft-11 (AM SMI VX'01 MW 14M) <br />'140r i* SiTf,'Si 5 <br />Sideslope Post -Peak Required Strengths <br />?{lit) SEYk? !rCRT,'k $tM ilX7tY:t 1 X YAGR'XS <br />Nmnal St,,% (Vel) —,._.�,,,,,,,.„,a ....... ......�. f �.,...,..,. <br />Page 6 <br />8/4/15 <br />( <br />Figure 2: Sideslope Liner System: (a) measured <br />ured peak strengths, (b) measured post - <br />peak strengths, (c) combination post -peak strength envelope, and (d) <br />comparison of combination post -peak strength envelope and design required <br />post -peak strengths <br />Figure 2(c) shows the combination post -peak strength envelope developed using the procedure <br />set forth in Stark and Choi (2004), which coincides with the post -peak strength envelope for the <br />GM/GC interface because sliding occurred along this interface for all of the normal stresses <br />tested in the single interface tests. If the critical interface changes with increasing normal stress, <br />combination strength envelope will also change interfaces as described by Stark and Choi <br />(2004). <br />Figure 2(d) adds the project specified strength envelope to the strength envelopes in Figure 2(c) <br />and in general shows the post -peak strength envelope of the GM/GC interface meets or exceeds <br />the project specified strength envelope especially at normal stresses greater than 6,000 psf based <br />on both single and multi -interface test results. However, at normal stresses of 1,000 and 4,000 <br />psf the measured interface strength is slightly lower than the required post -peak values (365 <br />&372 v. 404 psf and 1,154 & 1,135 v. 1174 psi), which is discussed below. It is anticipated this <br />small difference between the measured and required post -peak strengths at normal stresses less <br />than 4,000 psf will not impact the factor of safety significantly. It is my understanding the <br />0 <br />