岩溶疏干区基于强度折减法的覆盖层土体稳定性分析

Stability Analysis of Cover Layer Soil Based on Strength Reduction Method in Karst Drainage Area

为给岩溶覆盖区盖层土体的稳定性判别方法提供更多的有效途径,以岩溶疏干区典型圆柱状盖层土体为研究对象,基于传统的极限平衡法,首先建立了处于一定覆盖层厚度、土体重度、降雨积水深度及岩溶空腔跨度等条件下的覆盖层土柱c-tanφ临界线,在覆盖层土柱的渐进破坏过程中,土体的黏聚强度和内摩擦角发挥作用的大小和顺序是不同的,根据潘家铮原理假设二者沿着距离c-tanφ临界线最短的路径折减。然后利用强度折减法确定了黏聚强度和内摩擦角的折减系数,进而获得了岩溶覆盖区盖层土体的稳定系数计算式,定义了覆盖层土体稳定状态的可靠域及失效域。最后指出在圆柱状塌陷坑形成后由于应力重新分布和集中,塌陷坑有继续塌陷的可能,通过分析建立了塌陷坑稳定性判据系数,为圆柱状塌陷坑是否二次发育继续塌陷提供了判定依据。实例分析表明,基于强度折减法建立的稳定系数计算结果及利用塌陷坑稳定性判据系数对已有塌陷坑稳定性进行判定的结果与现实情况吻合良好,为岩溶覆盖区盖层土体的稳定性分析提供了理论依据。

In order to provide more effective ways to judge the stability of cover soil in Karst area,taking the typical cylindrical cap soil column in Karst dredging area as the research object,based on the traditional limit equilibrium method,the c-tanφcritical state line of the cover soil is firstly established under the specific thickness of cover soil,the weight of the soil,the depth of the rainfall and the diameter of the Karst cavity.In the progressive failure process of the cover soil,the cohesive force and the internal friction angle of the soil are different in size and order,according to the principle of Pan Jiazheng hypothesis,it is proposed that the two should be reduced along the shortest path from the current coordinate of strength parameter(c、tanφ)to c-tanφcritical state line.The strength reduction method is used to establish the coefficient of cohesion and friction coefficient reduction,and then the stability coefficient of cover soil in Karst area is obtained and the reliable domain and failure domain of the stable state of the cover soil are defined.Finally,it is pointed out that there is a possibility that the collapse pits may continue to collapse due to the stress redistribution and concentration after the formation of the cylindrical collapse pits.Through analysis,the stability criterion coefficient of collapse pit is established,which provides a judgement basis for cylindrical collapse pit s secondary development and continuing collapse.Case analysis shows that the calculation results of stability coefficient established by strength reduction method and determination of the stability of the existing collapse pit by using the criterion coefficient of the collapse pit are in good agreement with actual situation and provides a theoretical basis for the stability analysis of cover soil in Karst area.