地震作用下土质边坡张拉裂隙扩展机制及稳定性三维极限分析方法

In high intensive region, the failure mechanism of the slope is complicated because of the existence of tension cracks, which is induced by the earthquake. In this research project, field investigation, shaking table test, theoretical analysis and numerical simulation will be conducted to study on the failure mechanism of the earth slopes subjected to earthquake, and the tension cracks induced by the earthquake are taken into account simultaneously. Firstly, based on the filed investigation on the unstable slopes in the seismic region, the extension behavior of the tension cracks will be explored. Furthermore, the failure mechanism of some representative slopes subjected to seismic loads is investigated preliminarily. Secondly, in order to find out the mechanism of failure process of earth slops subjected to seismic loads, shaking table tests will be carried out. In addition, the quantitative analysis method to evaluate the cracks length induced by the earthquake will be presented as well, considering the effects of slope geometry, soil strength parameters and magnitude of seismic load. Thirdly, based on the theoretical analysis, and considering the effects of cracks length, the shape of the failure surface of the three-dimensional slope will be analyzed. A three-dimensional analysis of earth slope stability will be proposed by using the kinematic method of limit analysis. Finally, the results of shaking table tests, numerical simulations will be used to verify the theoretical analysis method. The results of this study have great academic contributions on the dynamic analysis of slope stability, which could provide theoretical foundation and technical support for the design of seismic slope engineering.

在高烈度地震区，地震作用下土质边坡的后缘张拉裂隙在三维空间上的不断扩展，决定了边坡破坏机制的复杂性。本项目采用现场调查、振动台试验、理论分析和数值模拟相结合的方法对此问题开展深入研究。首先通过对地震灾区大量失稳土坡的现场调查，获得坡体后缘张拉裂隙扩展特征，确立地震土坡典型失稳破坏模式；然后，采用振动台模型试验，研究典型土坡在地震荷载下的失稳破坏过程，考虑坡面形态、土体强度参数、地震荷载强度等要素，深入揭示地震土坡失稳机理，提出定量反映坡体后缘张拉裂隙空间扩展规律的分析模型。在由此确定的地震土坡张拉裂隙分析模型的基础上，建立基于极限分析上限定理的土坡三维稳定性分析方法，并提出土坡在地震过程中伴随张拉裂隙扩展的潜在最危险滑面演化模式。最后，通过理论、试验和数值模拟结果的综合对比分析，验证与完善理论分析方法。本研究可深入揭示地震土坡空间失稳破坏演化机制，具有重要的理论意义和工程应用价值。

现场调查、室内试验以及理论分析的变分法都已经证明边坡后缘拉应力区的存在，在地震荷载下，由拉应力引起的拉裂面对边坡稳定性的影响已被诸多学者所关注。但在传统的分析方法中，往往只考虑了岩土体在剪应力作用下发生破坏造成边坡失稳，而忽略了边坡拉应力的影响，这将造成对边坡稳定性的高估，给工程带来隐患。本项目围绕围绕地震条件下边坡后缘拉应力区分布范围以及坡体空间三维边界效应分析中的关键科学问题，通过现场调查、理论分析、物理试验、数值模拟相结合的手段，从边坡几何特性与土体材料特性两个方面展开研究，系统分析了土质边坡受地震荷载影响的破坏机理。针对前者，提出了能考虑坡体宽度限制边界效应，能揭示三维破坏模式与二维平面破坏模式差异的裂隙边坡稳定性分析方法。发展了基于极限分析上限法的三维边坡分析理论，揭示了坡体后缘张拉裂隙极限深度的演化规律，探讨了地震荷载对三维边坡破坏机制的影响。分析表明，裂隙的存在会使边坡的稳定性系数有所降低，这一减小的趋势随着边坡宽度的增加而增加；地震条件下与二维平面应变模型相比，三维裂隙边坡呈现出浅层的破坏模式。对于后者，从土体材料抗拉强度实验值比理论值偏小这一事实出发，引入了修正的莫尔库伦破坏准则，缩减了土体的抗拉强度，提出了地震土坡张拉截断的破坏模式。以更接近材料真实强度参数的理论模型为基础，建立了非线性强度准则下的边坡稳定性分析方法，结合极限分析原理和有限元方法探讨了地震荷载对边坡潜在滑面位置以及坡体稳定性的影响；开展了关键参数的敏感性分析，揭示了土体强度参数、抗拉强度折减系数、地震动荷载参数、坡体几何参数等对边坡稳定性的影响。通过以上研究，实现了对坡体内的张拉应力影响分析，提出了较为系统的边坡在拉-剪复合破坏机制下的稳定性分析方法，可为高烈度山区的边坡防护工程提供科学依据。