Title: Enhanced Anisotropic Bounding Surface Model
Description: This dissertation describes the application of an enhanced anisotropic bounding surface model with non-associative flow rule, based on the anisotropic critical state theory and bounding surface plasticity. The model has exhibited a great potential to realistically simulate the mechanical behavior of cohesive soils, in non-linear finite element method associated with the coupling analysis for simulating deep excavation induced ground deformations. The first phase of this research illustrates efforts in integrating the enhanced anisotropic bounding surface model into finite element analysis (FEA) software. The implementations are validated against undrained isotropic and anisotropic triaxial test results for various types of cohesive soils, including those with strain softening behavior. The capability and limitation of the bounding surface models are assessed, and it is confirmed that complex soil behavior, such as the effects of stress anisotropy and over-consolidation nature, can practically be simulated using such bounding surface models integrated in FEA, especially for normally and overly consolidated Kaolin and Taipei silty clay specimens.

Phase two presents the application of bounding surface models for the finite element deep excavation analyses. The simulations are evaluated through comparison with field measurements in Taipei City (TNEC and WTC sites) and Boston City (Post Office Square site). The case studies have demonstrated satisfactory agreement between the simulations and field measurements, especially for the TNEC and Post Office Square sites, while there is a less satisfactory agreement for the WTC site. Similar results are obtained for the different versions of bounding surface model, except that the isotropic version of the model tended to under-estimate the lateral deformation. The importance of adopting anisotropic hardening rules and a bounding surface in simulating for a more realistic ground response has been established due to the better simulation capability of the enhanced bounding surface model than that of some other bounding surface models. In addition, the difference in results between the non-associative and associative versions of bounding surface model was found to be rather negligible in the case of finite element analysis of deep excavation involved with collapse.