反倾岩质边坡次生倾倒机理及稳定性分析

倾倒破坏是反倾边坡的一种常见破坏模式,其中次生倾倒是反倾岩质边坡倾倒破坏的主要诱因。建立了反倾岩层在坡后土体作用下次生倾倒破坏的地质力学模型,基于室内物理模拟试验,分析了反倾岩层上覆土压力分布规律、岩层的破坏模式和整体破坏面的形状与位置。根据库仑主动土压力理论得到下卧岩层表面各点法向压力的理论值与实测值基本相符,土体中存在土拱效应导致两者存在差异,随着上覆土体厚度及堆载作用的加大,土拱效应越明显。各岩层可能的破坏模式包括弯拉破坏、弯滑破坏和滑动破坏。下卧反倾岩层的整体破坏面是一通过坡脚的近似平面,整体破坏面与岩层层面法线方向呈0°~25°的夹角。基于叠合悬臂梁模型,引入岩层横截面上节理面的黏聚力和岩石抗拉强度随岩层嵌入深度的折减系数,改进了反倾岩层的极限平衡分析方法,推导了坡体任意岩层下推力的理论公式,定义了任意岩层变形破坏的安全系数和边坡整体倾倒破坏的综合安全系数。提出了下卧反倾岩层潜在整体破坏面的理论计算方法,并确定了影响潜在整体破坏面位置的敏感因素。

Mechanism and stability of secondary toppling of counter-tilt rock slopes

Among kinds of toppling failures of anti-dipping rock slopes, the secondary toppling is the main inducement. The geo-mechanical model for the secondary toppling of the anti-dipping rock strata under the action of the soil behind the slope is established. Based on the laboratory physical simulation tests, the distribution laws of earth pressure on the surface, failure modes, shapes and positions of the integral failure surface of the counter-tilt rock strata are analyzed. According to the Coulomb's active earth pressure theory, the theoretical values of normal pressure at each point on the underlying stratum surface are basically consistent with the measured values, but the soil arching effect leads to the difference between them. With the increase of overlying soil thickness and surcharge effect, the soil arching effect becomes more obvious. The possible failure modes of various strata include bending failure, bending-slip failure and sliding failure. The integral failure surface of the underlying anti-dipping rock stratum is an approximate plane through the foot of the slope, and the angle between the integral failure surface and the normal direction of the rock strata is 0°~25°. Based on the superimposed cantilever beam model, the limit equilibrium analysis method of anti-dipping rock strata is improved by introducing the reduction coefficient of the cohesion of joints on the cross-section of rock strata and the tensile strength of rock with the embedded depth of rock strata. The theoretical formula of thrust for arbitrary stratum in the slope is derived. The safety factors of deformation and failure of arbitrary rock stratum and the comprehensive safety factor of the whole slope collapse are defined respectively. The theoretical method for calculating the potential integral failure