| Wave propagation in saturated soil and sand liquefaction are two important subjects in earthquake engineering and geotechnical engineering. In this dissertation, after making a short review of the state-of-the-art of studies on the topics, the author present the study results, which include the following contents:(1) After simply reviewing the research results of two-dimensional wave propagation in the non-deformable porous media, a series of studies on wave propagation in the deformable porous saturated soil layers are made. They include compiling a computer program which permits to incorporate various constitutive relation of soil skeleton, dilatancy, stiffness deterioration etc. Comparative studies are made for various cases of soil stiffness, resistance of percolation, drain condition on boundary, loading form, constitutive relation, and stratification. As a consequence, some new trends and phenomena are discovered.(2) Some studies are made for the subject of various effects on wave propagation and ground motion of multi-dry, multi-saturated, and alternate dry and saturated soil layers. A comprehensive computer program is compiled, accounting for soil dilatancy, linear and non-linear constitutive relation, rigidity degradation and suiting to any combinations of soil layers, dry and/or saturated with different thicknesses, properties, continuity conditions at interfaces, and inputs at base and top boundaries. From the numerical results obtained for a quite large number of typical cases, some knowledge of general trends of response for, especially, the cases of alternate dry and saturated soil layers are gained both quantitatively and qualitatively. Therefore, some conclusions and suggestions are presented.(3) A new approach being able to provide more thorough understanding of the mechanism of soil liquefaction is presented. The approach consists of accounting for the soil-water interaction, regarding the dilatancy as a source term enabling relative motion between soil and water to occur, and simultaneously solving these equations to obtain the details of development of the stress and motion of soil and water. After some numerical analyses, the effects of dilatancy, constitutive relation, rigidity degradation, thickness, properties, continuity conditions at interfaces are analyzed.(4) An introduction of the background that makes us present this study is made. Based on some macroscopic evidences gained in actual earthquake fields and on a preliminary theoretical analysis, it has been pointed out that the Rayleigh waves should be an essential cause of liquefaction for the fields beyond the epicentralregion with saturated sand deposits at shallow depths. After the simple analyses with the single phased media theory, a more detailed analyses has been done, based on two phased media theory, on Rayleigh wave propagation in saturated soil. The new results show that Rayleigh wave will really cause larger shear stress and pore pressure than S wave in shallow layers and thus easily induce sand liquefaction.(5) Based on an empirical formula, in terms of soil shear velocity, to evaluate soil liquefaction, which is simple to handle and prospective in further application, the author presents, in the probabilistic and fuzzy way, the formulae for the evaluation of liquefaction probability and fuzzy probability at given depths and for a fuzzy evaluation of liquefaction hazard of the total soil layers. A probabilistic liquefaction index and a fuzzy probabilistic liquefaction index are tentatively suggested to show approximately the liquefaction hazard of soil layer in an indeterministical way,(6) By taking the advantage of Seed's simplified method for free ground sites and of the cone model concept well developed by Meek and Wolf in dynamics in recent years, a new simplified method is presented on the basis of a review of the limited number of literature in respect of model tests and finite element analysis on the sand liquefaction evaluation of subsoil of buildings. It is concluded that the effec...
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