Mechanism Investigation And Numerical Simulation Of Evolution Of Shear Band In Soil

The initiation and evolution of shear band in soil is one of the hotspots and key issues in geotechnical engineering and a large number of achievements have been obtained. However, so far studies on the mechanism of evolution of shear band is still inadequate, while numerical simulation of strain localization such as shear band also needs improvement. Based on those achievements, a rational approach was explored for simulating and tracing the evolution process of shear band in soil from aspects of experimental study, mechanism analysis, numerical implementation and preliminary application. The main achievements obtained in the thesis are as follows:A series of model tests were performed to investigate the mechanism of evolution of shear band preset in artificial structured soil samples by using a self-made geotechnical model test apparatus and the according procedures. The results and further analysis revealed that, the phenomena of stress concentration and redistribution exists around the tip of shear band preinstalled due to the lack of shear resistance on it, which then causes the stress axes deflection in the tip area.The difference and discontinuity of stress states between two sides of a shear band around the tip result from the stress concentration and redistribution in the tip area of shear band in soil, which causes further evolution of shear band to be local dominant. Therefore, a generalized local dominant analysis method for shear band evolution was proposed. This method can describe the influence of stress concentration and redistribution in tip area on the direction and process of evolution of shear band, and can explain the mechanism of stress axes deflection in the tip area reasonably.A simple integration scheme was presented for the numerical quadrature of discontinuous zone in extended finite element method (XFEM) to guarantee the compatibility of XFEM to non-linear constitutive models. A contact algorithm based on XFEM was also established, which can reflect the dissipation mechanism of frictional contact reasonably and therefore avoid the phenomenon of zero energy dissipation. The modified XFEM has the ability to describe moving discontinuities such as shear band in soil.A XFEM simulating system for tracing shear band evolution in soil was established by integrating the local dominant analysis method into the modified XFEM program. Model tests of evolution of shear band in soil were simulated by this system and the results agree reasonably with those experimental results.Numerical simulations were performed on several boundary value problems. Reasonable results were obtained, among which the simulated mechanism and process of the failure of the Carsington embankment agree well with the observed result. It proves that mechanism investigation of evolution of shear band in soil proposed by this thesis is reasonable and the local dominant analysis method is feasible and applicable.