基于整体刚体平衡法的膨胀土边坡稳定分析

Analysis of expansive soil slope stability based on whole rigid body equilibrium method

膨胀土边坡危险滑面受裂隙面影响,常位于强弱风化层界面,且近似为直线,滑坡后缘一般为垂直张拉裂缝,下部主滑床呈近水平状。基于上述特性,提出滑坡体的三折线刚体简化模型,滑体内土体强度采用多次干湿循环后稳定值,并根据整体刚体的静力平衡推导建立边坡安全系数求解公式。以秦淮东河膨胀土边坡为实例,开展膨胀土干湿循环室内试验,并利用推导公式求解边坡长期稳定系数,计算结果与FLAC强度折减法求解结果接近。设计程序分析了强风化层厚度和膨胀土层厚度对边坡安全系数求解值的影响,发现后者随前两者的变化先急剧减小后趋于平缓,在一定范围内影响较大。考虑浅层土体强度和强风化层深度在干湿循环不同阶段的变化,求解了各阶段强弱风化层交界面上滑面的安全系数,发现其呈现指数衰减的趋势,边坡主要在6次干湿循环后发生失稳,滑面深度在1.83 m左右。

The sliding surface of the expansive soil slope affected by fracture surface, always locates in the severe and mild weathered layer interface and approximates to a straight line. The trailing edge of landslide is generally vertical tension crack. The lower main slip bed is nearly level. Based on the above characteristics, a simplified model of three-broken line rigid bodies is proposed, where strength of soil in sliding body uses stable values after repeated wet-dry cycles. According to the static equilibrium of the whole rigid body, the solution formula of the safety factor of the slope is established. Taking the Qinhuai River expansive soil slope as an example, dry and wet cycling laboratory test of expansive soil is carried out. The formula is used to calculate the long-term stability coefficient of the slope, and the result is close to that of the FLAC strength reduction method. And it can also reflect the adverse effect of the fracture on the force of the sliding body. The influence of the thickness of the severe weathered layer and the thickness of the expansive soil layer on the value of the safety factor of the slope is analyzed by designed program. It is found that when the former two thicknesses increase, safety factor of the slope firstly decreases sharply and then tends to slow. And considering the shallow soil layer strength and the severe weathering depth changes, the safety factor of severe weathering layer interface in different stages of dry-wet cycles is analyzed. It is discovered that the safety factor exhibits the trend of exponential decay; and the slope loses stability mainly after six cycles of wetting and drying. The depth of sliding surface is about 1.83 m. © 2016, Science Press. All right reserved.