Laserfiche WebLink
Taj Bahadori <br />July 13, 2015 <br />Page 4 of 6 <br />• We attempted to evaluate if GCL with a higher peel strength would resist the 0 <br />internal failure and repeated the test at 12,000 psf normal stress using GCL <br />sample with nearly the largest peel strength, 58.1 lbs. This retest also showed <br />internal GCL failure with a post -peak strength of 1195 psf vs. specified minimum <br />of 1575 psf. The peak strength for this retest was 7,104 psf corresponding to a <br />secant interface friction angle of 30.6 degrees, too high to prevent GCL <br />needlepunch thread rupture and thus resulting in GCL internal failure. <br />Test Series 2 — GCUHDPE Geomembrane (GM) Interface <br />• The test results for this test series met the specification requirements for post - <br />peak strength at each of the 5 normal stress points. Internal GCL failure was <br />observed at 12,000 psf normal stress, but the post -peak interface shear strength <br />was 1,609 psf, greater than the minimum specified value of 1575 psf. The GCL <br />used for all 5 points of this test series had a peel strength of 53.6 lbs. <br />• At each of the 5 normal stresses, the peak strengths for the GCL/GM interface <br />were lower than the corresponding peak values for Test Series 1 (foundation <br />layer/GCL interface). This would suggest that, in the base composite liner <br />system, the GCL/GM (and not the foundation layer/GCL) interface is the weakest <br />interface. <br />® Due to a concern of the Design A-E firm that the above interpretation may not be <br />conclusive, since the peak strengths for Test Series 2 (GCL/GM interface) were <br />lower but not significantly lower than for Test Series 1 (foundation layer/GCL <br />interface), multi -layer (sandwich) interface tests were performed upon <br />direction and approval by the County. Since there is no pre -defined failure <br />interface in sandwich tests, they provide the interface strengths along the <br />weakest interface in the composite liner systems and also identify that weakest <br />interface. Sandwich interface tests were performed and used for previous <br />Module 1 liner for the Foothill Landfill and also for the North County Landfill <br />Area 4 and 5 composite Liners. <br />c: <br />PA14 Projects\14-101 ( SJCDPW North County and Foothill)\Correspondence\Memo - Foothill Interface Shear Strength Test Results.docx <br />