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，塑性上界定理和下界定理是评价地构体系稳定性和崩塌荷载的主要工具。PI最近的一项研究表明，基于这些定理的分析可能会严重高估崩塌荷载以及边坡和土壤堤防的安全系数。造成这种高估的主要原因是上界定理和下界定理中的正态性假设和固有的高膨胀角（等于摩擦角）假设，这意味着膨胀体积变化大得不切实际。为了克服这一缺陷，需要采用合适的本构模型来准确地模拟土的体积变化。此外，由于土体的抗剪强度直接受其体积变化的影响，精确的土体模型将自动模拟致密颗粒土的软化过程。这种峰后土体的行为也会影响岩土系统的稳定性。在数值模拟的背景下，非正态性和软化都会导致与局部剪切变形的启动直接相关的重大困难。本文拟研究应变局部化和土体体积变化对土路堤坍塌的影响。膨胀土的响应将在临界状态土力学的框架内进行建模。采用非关联Mohr-Coulomb模型和临界状态二面塑性模型，研究土体体积变化和诱导应变软化对土质边坡稳定性的影响。考虑到应变软化会导致系统处于失稳边缘的某些部分发生显著的局部变形，将开发增强的有限元技术和本构模型来处理系统的分岔后行为。调查结果将以适当的图表形式呈现，可作为纳入土壤膨胀对边坡稳定性影响的指南。

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.