| An experimental study aimed at improving the understanding of the mechanics of liquefaction is presented. Two aspects of the undrained behaviour; (i) the influence of initial state, characterized by void ratio, principal stresses and their directions, and fabric under a given undrained stress path, and (ii) the effect of undrained stress path at a given initial state, were studied in a systematic manner. Triaxial, simple shear and hollow cylinder torsional shear devices were used in the experimentation to enforce a range of stress paths that simulate the loading in situ. The effect of membrane penetration was duly addressed in order to confidently measure the truly undrained behaviour of sands.; The influence of soil fabric was determined using triaxial and simple shear tests on specimens reconstituted by different techniques. In addition to specimens reconstituted in the laboratory, undisturbed, in-situ frozen sands from four different sites were tested to assess the relevance of the behaviour of reconstituted specimens to the sand in-situ. It is shown that in-situ sands and those water pluviated in the laboratory are inherently anisotropic, and their undrained behaviour is direction dependent.; It is shown that the initial effective stress state plays a dominant role on the subsequent undrained behaviour at a given void ratio. Hollow cylinder torsional shear tests on water pluviated fabric were used to assess the influence of the initial axisymmetric and non-axisymmetric stress states on undrained shear. The behaviour due to an increase in deviator stress alone, and that due to simultaneous changes in deviator stress and the direction of principal stresses is investigated.; It is shown that both steady state and quasi steady state can be treated within the same framework. The friction angle mobilised at these states is independent of fabric, void ratio, effective confining and static shear stress levels, direction of principal stresses, and undrained stress path. (Abstract shortened by UMI.)... |
