UBC Theses and Dissertations
Static, cyclic and post liquefaction simple shear response of sands Sivathayalan, Sivapathasundaram
An experimental study of static, cyclic and post cyclic undrained simple shear response of reconstituted water pluviated Fraser River sand is presented and compared to its triaxial behaviour from an earlier study. Static and cyclic behaviour was assessed over a range of void ratios that included the loosest deposition state using different confining stress levels. The effect of reconstitution technique on undrained behaviour was also investigated. It is shown that the method of specimen reconstitution has a profound influence on its undrained response. If laboratory results are to be meaningful in field application, the specimen reconstitution technique must duplicate the deposition process of the deposit to be modelled. The static undrained response in simple shear is contractive only for the loosest of the accessible void ratios, regardless of the level of confining stress. For a given initial void ratio and confining stress level, simple shear response is much less contractive than triaxial extension response. The criteria for contractive deformation during cyclic loading based on triaxial studies are shown to be also valid under cyclic simple shear. The influence of confining stress level on liquefaction resistance is shown to increase with relative density in a manner similar to that found under triaxial conditions. The cyclic resistance at the loosest state is essentially independent of the confining stress level. At denser states, however, the reduction factor K in simple shear is not as high as under the triaxial conditions. The reduction factor C used to adjust cyclic triaxial liquefaction resistance to an equivalent field simple shear condition is shown to be larger than currently adopted in design, and its value is dependent on both density as well as confining stress level. The strain level over which sand deforms essentially at zero stiffness in post liquefaction loading is dependent on relative density and maximum strain experienced during cyclic loading. Post liquefaction response of cyclically liquefied sand is shown to be essentially similar to that of the sand liquefied by static load-unload cycle. The undrained simple shear and triaxial behaviour of the silty Syncrude sand is shown to be, in general, similar to that of Fraser River sand.
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