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BRAY, RATHJE, AUGELLO AND MERRY D Seismic Design for Lined Solid-Waste Landfills <br />211GEOSYNTHETICS INTERNATIONAL S 1998, VOL. 5, NOS. 1-2 <br />ure(ontheorderof5000%/minute or5Hzloading to15%strain).These resultsindicate <br />that the failure strain for commercially available, untextured HDPE geomembranes is <br />at least 10% (Merry 1995). In addition, cyclic multiaxial tension test results indicate <br />that HDPE geomembranes can undergo cyclic loadings at less than their peak strength <br />without losing ductility and strength (Figure 5b). <br />Cyclic wide-strip uniaxial tests were also performed by the authors ofthe current pa- <br />per,andthese testsindicated that thefailure strain foruntextured HDPEgeomembranes <br />was at least 15%. Moreover, some HDPE geomembrane specimens were loaded be- <br />tween 5and 20%strain ata frequency of1Hz for500cycles without rupturing; howev- <br />er, there was significant modulus degradation in these tests. Geomembranes may pos- <br />sess sufficient ductility to deform rapidly during an earthquake without failing, but <br />additional experimental work is warranted to verify this finding. <br />Figure 5. Stress-strain-time multiaxial response of a smooth HDPE geomembrane: <br />(a) monotonic strain-controlled loading; (b) quasi-cyclic loading (adapted from Merry <br />1995). <br />0102030 <br />0 <br />10 <br />20 <br />30 <br />40 <br />0102030 <br />0 <br />10 <br />20 <br />30 <br />(a) <br />(b) <br />Strain (%) <br />Strain (%)Stress (MPa)Stress (MPa) <br />Merry and Bray (1997a) variable n <br />th-order parabola <br />Denotes predicted failure strain from n <br />th-order parabola <br />1000%/minute 10%/minute <br />1%/minute <br />0.0004%/minute <br />0.01%/minute <br />0.1%/minute <br />Smooth HDPE geomembrane <br />Temperature = 21 _á1_C <br />Quasi-cyclic loading (see below) <br />Primary loading at 1%/minute <br />1.5 mm thick, smooth HDPE geomembrane <br />Temperature = 21 _á1_C <br />Experimental results from multiaxial tests <br />t,t < 5 minutes <br />3.2 sin(¶/10(t - 5)) + 5, 5 minutes <t < 65 minutes <br />t ---60,t > 65 minutes <br />«(%) =