ARCHIVED REPORTS_2015 - Laserfiche WebLink

Home Browse Search

Interpretation of SGI Interface Shear Strength Test Results Page 7 Foothill Sanitary Landfill - Area 2A Liner System 8/4/15 is Design Engineer has been asked to obtain a variance to the contract specifications for this difference and they approved the use of the supplied GM and GC materials. If the geosynthetics and soils used during actual construction differ from the materials tested by SGI, the lowest post - peak strength envelope and critical interface could change. v In summary, the critical interface for the sideslope liner system materials tested by SGI is the GM/GC interface. The GM/GC post -peak strengths for the sideslope liner system meet or exceed the project specified post -peak strength envelope except are slightly below the specified values at normal stresses of 1,000 and 4,000 psf but this small difference is being accounted for by the designer. 4.0 Base Liner Interface Test Results Figure 3 presents the interface strength test results for the base liner system that are presented in Table 1. Each of the strength envelopes are keyed to the Test Series name in Table 1. For example, Figure 3(a) presents the peak interface strengths for Test Series 1 and 2 because these single interface test series were specified to assess the strengths of the various components in the base liner system. In addition, the multi -interface test series for the base liner system (Test Series 4 — Base Multiple) with all of the interfaces tested in Test Series 1 and 2 is included for comparison purposes. Figure 3(a) shows the weakest/critical interface of the base interfaces tested is the GM/GCL interface. The GM/GCL interface shows slightly lower strengths than the GCL/FLS interface for all normal stresses tested. There is not a large difference in the interface strengths for Test Series 1 and 2 so it is beneficial that a multi -interface test was conducted using the base liner system materials. The critical interface for the base liner system of GM/GCL was confirmed by Multi -Interface Test Series 4, which shows shear displacement occurred along the GM/GCL interface for all of the normal stresses tested except 1,000 psf where it occurred on the GM/gravel interface as discussed below. This confirms the critical interface for the base liner system materials tested is the GM/GCL interface and the single and multi -interface tests yield similar peak strengths, which is in agreement with Stark et al. (2015). If the geosynthetics and soils used during actual construction differ from the materials tested by SGI, the critical interface and lowest peak strength envelope could change which would change the design post -peak envelope. 7