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，塑性力学的上、下限定理是评价岩土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壤保护层的倒塌荷载和安全系数。 这种高估的主要原因是上界和下界定理中的正态性假设和固有的大膨胀角（等于摩擦角）假设，这意味着不切实际的大膨胀体积变化。 为了克服这一缺陷，应采用能准确反映土体体积变化的本构模型。此外，由于土壤的抗剪强度直接受到其体积变化的影响，因此精确的土壤模型将自动模拟密实颗粒土壤的软化。土壤的峰后特性也会影响岩土系统的稳定性。在数值模拟的背景下，非常态和软化引起显着的困难，直接关系到启动的局部剪切变形。 本文拟探讨应变局部化和土体体积变化对土体压溃的影响。将在临界状态土壤力学的框架内模拟非平衡土壤响应。本研究会选用不同的塑性模型，包括非结合Mohr-Coulomb模型及临界状态两表面塑性模型，以研究土体积变化及诱发应变软化对土质斜坡稳定性的影响。考虑到应变软化将导致系统某些部分处于不稳定边缘的变形显著局部化，将开发增强的有限元技术和本构模型来处理系统的分叉后行为。调查结果将以适当的图表形式呈现，这些图表可用作将土壤粘性对边坡稳定性的影响纳入考虑的指南。

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.