【作者】 喻葭临；

【导师】 张丙印； 于玉贞；

【作者基本信息】 清华大学 ， 土木工程， 2009， 博士

【摘要】 土中剪切带萌生和扩展问题一直是岩土工程领域的研究热点和难点之一,并取得了大量的成果。但目前对已有剪切带扩展机理的研究较少,对剪切带等应变局部化现象的模拟也不十分理想。本文在前人研究成果的基础上,从土中剪切带扩展模型试验、扩展机理分析、数值实现到初步应用,探索了一条模拟和追踪土中剪切带扩展过程的合理途径。论文的主要新成果有:(1)初步探讨了人工制备结构性土中已有剪切带扩展的模型试验方法,自行研制了剪切带扩展模型试验装置,进行了多组模型试验。试验结果和对比分析表明,已有剪切带上的抗剪能力不足以提供实际所需抗剪能力时,尖端附近区域将存在应力集中和重分布,并导致尖端附近区域的应力主轴偏转现象。(2)土中已有剪切带尖端的应力集中和重分布将表现为尖端两侧应力状态的差异性和不连续性,使得剪切带的进一步扩展具有区域选择性。提出了一种新的更一般的区域控制剪切带扩展分析方法,该方法较全面地考虑了尖端应力集中和重分布对扩展过程和方向的影响,并可结合传统强度理论合理地解释尖端附近区域的应力主轴偏转机理。(3)提出了一种扩展有限元法(XFEM)中非连续区域的简易积分方法,保障了XFEM对于非线性材料本构的兼容性。构建了基于XFEM的界面接触算法,该算法合理地反映了摩擦接触的耗散机制,从而避免了零能耗散现象。改进后的扩展有限元法具备了描述土中剪切带等运动的不连续位移场的能力。(4)通过构造适当的算法和判据,将区域控制扩展分析方法集成到改进的XFEM程序中构建了追踪土中剪切带扩展过程的扩展有限元模拟系统,对土中剪切带扩展模型试验进行了模拟并取得了合理的结果。(5)应用此模拟系统对多个边值问题进行了模拟研究,取得了合理的结果,特别是较好地揭示了Carsington堤坝的失稳机理。这表明本文对土中剪切带扩展机理的分析是合理的,所提出的区域控制扩展分析方法实用可行。更多还原

【Abstract】 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.更多还原