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BRAY, RATHJE, AUGELLO AND MERRY D Seismic Design for Lined Solid-Waste Landfills <br />210 GEOSYNTHETICS INTERNATIONAL S 1998, VOL. 5, NOS. 1-2 <br />Kavazanjian et al. (1995) <br />Augello et al. (1998) <br />Figure 4. Strain dependent shear modulus reduction and damping curves for <br />municipal solid-waste. <br />0.0001 0.001 0.01 0.1 1 10 <br />Shear strain (%) <br />0.0 <br />0.1 <br />0.2 <br />0.3 <br />0.4 <br />0.5 <br />0.6 <br />0.7 <br />0.8 <br />0.9 <br />1.0 <br />0 <br />5 <br />10 <br />15 <br />20 <br />25 <br />30 <br />Idriss et al. (1995) <br />GeoSyntec (1996)G/GmaxDamping (%) <br />Several studies have been completed on the long-term static response of geomem- <br />branes (e.g. Giroud and Beech 1989; Koerner and Hwu 1991; Bourdeau et al. 1993; <br />Merry and Bray1997a,b). However,relatively little attention hasbeen givento theper- <br />formance of geosynthetic materials during dynamic loading. Hence, the ductility of <br />these materials under rapid monotonic and cyclic loading requires characterization. <br />Strain-controlled multiaxial tension test resultspresented byMerryand Bray(1997a) <br />over a strain rate range of 10 to 0.0004%/minute indicate that the visco-elastoplastic <br />response of HDPE and PVC geomembranes follows a well-defined, tractable pattern <br />(Figure 5a). Experimental results indicate that the secant Young’s modulus softens, <br />maximum stress at failure reduces, and failure strain (i.e. strain at maximum stress) in- <br />creases as the strain rate decreases. A number of proposed numerical models, such as <br />rate-dependent hyperbolic and n <br />th-order parabolic functions and an adaptation of the <br />Singh and Mitchell (1968) creep model, have been shown to capture the stress-strain- <br />time-temperature responseofHDPEwell overfourordersofstrain rate (e.g. Merryand <br />Bray 1997a,b). <br />These numerical models, when used to extrapolate standard test results to higher <br />strain rates, suggest that the failure strain of HDPE reduces significantly under rapid <br />loadings. This potential increase in brittleness of HDPE at strain rates representative <br />of those expected during seismic events warrants concern, and experimental data are <br />required to verify this predicted response. <br />Multiaxial tests have been performed on 1.0 and 1.5 mm thick, smooth HDPE geo- <br />membrane specimens byinducing a static strain of5% and then loading rapidly to fail-