Role of Strain Localization and Dilatancy on Deformation and Stability of Soil Slopes

除了传统的极限平衡方法外，塑性上下限理论是评价土工结构体系稳定性和破坏荷载的主要工具。PI最近的一项研究表明，基于这些定理的分析可能会大大高估斜坡和土质路堤的坍塌荷载和安全系数。这种过高估计的主要原因是正态假设和上下界定理中固有的高膨胀角(等于摩擦角)的假设，这意味着不切实际的大膨胀体积变化。为了克服这一不足，必须采用能够准确模拟土体体积变化的本构模型。此外，由于土体的体积变化直接影响土体的抗剪强度，精确的土体模型将自动模拟密实颗粒土的软化过程。土体的这种峰后性态也会影响岩土系统的稳定性。在数值模拟的背景下，非正态和软化都造成了与局部剪切变形的开始直接相关的显著困难。提出了应变局部化和土体体积变化对土质路堤坍塌的影响。膨胀土的响应将在临界状态土力学的框架内模拟。选择了从非关联Mohr-Coulomb模型到临界状态两种塑性模型来研究土体体积变化和诱发应变软化对土坡稳定性的影响。考虑到应变软化将在系统处于失稳边缘的某些部分引起显著的局部化变形，将发展增强的有限元技术和本构模型来处理系统的分叉后行为。勘察结果将以适当的图表形式呈现，可作为考虑土体剪胀对斜坡稳定性影响的指导原则。

In addition to traditional limit equilibrium methods, the upper bound and lower bound theorems of plasticity are the main tools in evaluation of stability and collapse load of geo-structural systems. A recent study by the PI shows that an analysis that is based on such theorems may significantly over-estimate the collapse load and the factor of safety of slopes and soil embankments. The main cause of such over-estimation is the assumption of normality and the inherent assumption of high dilation angle (equal to friction angle) in the upper bound and lower bound theorems, which implies an unrealistically large dilatational volume change. In order to overcome this deficiency, a proper constitutive model that can accurately model the volume change of the soil should be used. Moreover, since the shear strength of the soil is directly affected by its volume change, an accurate soil model will automatically simulate the softening of dense granular soils. This post-peak behavior of the soil will also affect the stability of a geotechnical system. In the context of numerical simulations, both non-normality and softening cause significant difficulties that are directly related to initiation of localized shear deformations. Here it is proposed to investigate the effects of strain localization and soil volume change on the collapse of soil embankments. The dilatational soil response will be modeled within the framework of critical state soil mechanics. A selection of plasticity models ranging from non-associative Mohr-Coulomb model to a critical state two surface plasticity model will be employed to examine the effect of soil volume change and induced strain softening on the stability of soil slopes. Considering the fact that strain softening will cause significant localization of deformations in certain parts of the systems that are on the verge of instability, enhanced finite element techniques and constitutive models will be developed to handle the post-bifurcation behavior of the systems. The results of the investigation will be presented in form of appropriate charts that may be used as guideline for incorporating the effect of soil dilatancy on slope stability.