| Summary: | 博士 === 國立臺灣科技大學 === 營建工程技術學系 === 86 === This study is to develop constitutive models for the stress-strain behavior of two cross-anisotropic materials: cohesive soil and grout column reinforced cohesive soil. These models are modified from anisotropic nested yield surface models. Both of them can take into account the influence of non-linearity, stress path-dependence,stress induced anisotropy, and the post-peak strain-softening behavior when soils are subjected to plastic deformation, and the influence of isotropy and elasticity when soil issubjected to elastic deformation. Parameters needed for the proposed models can be obtained directly from the CK0U triaxial compression and extension tests. The applicability of these models to the cohesive soil and the grout column reinforced cohesive soil with low improvement ratio (<5%) has been verified under undrained condition by the K0 consolidated plain strain tests and true triaxial tests. By combining with the base failure mechanism suggested by the Architectural Institute of Japan, an analy-tical method for evaluating the undrained base stability of a deep excavation in anisotropic soil has been derived from the proposed model. This base stability model accounts for the mechanical behavior of soil under plane strain condition, inherent strength anisotropy and non-homogeneity of naturally deposited soil, and geometry of excavation (i.e., width of excavation and depth of excavation wall etc.). But it does not deal with the factors such as stiffness of excavation wall and the stiffness and spacing of internal braing. The suitability of this method for analyzing base stability of deep excavations is verified by comparison with the numerical study results of deep excavations in Boston and a base failure case in Taipei.
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