悬臂-拉裂式崩塌破坏机制研究

悬臂-拉裂式崩塌是崩塌类型中较为常见的一种，常发育于近水平层状的陡峻岩质边坡，在我国的西南和西北山区以及三峡库区，该类危岩体的数量多且崩塌发生频率高。调查研究表明，差异风化剥蚀、河流侧蚀、海水浪蚀、碳酸盐溶蚀等作用是岩质边坡产生凹进岩腔和凸出悬臂的外动力地质作用。在调查基础上，概化出厚层硬岩夹薄层软岩和薄层硬岩夹软岩两种悬臂梁崩塌破坏模式。根据悬臂梁最大弯曲应力计算理论，推导出岩腔极限深度计算公式，并结合岩石风化剥蚀速率，对悬臂梁危岩体产生破坏的时间进行了预测。通过岩腔极限深度计算公式的分析和悬臂梁崩塌野外调查结果，均表明岩腔极限深度与悬臂岩体厚度成正相关，而与顶部裂缝深度比成负相关。根据最大拉应力-抗拉强度比值分析法，推导出悬臂梁危岩体稳定系数计算公式，并给出其稳定性评价标准。通过典型算例，对文中方法的正确性进行检验，结果表明该方法具有公式简单和计算可靠等优点。

Research on failure mechanisms for cantilever and tension crack-type collapse

The cantilever and tension crack-type collapses, which often occurred in steep rock slopes with nearly horizontal layered stratum, are very common in nature. This kind of perilous rock mass is not only much in quantity but also high in frequency of occurrence in mountainous areas of southwest and northwest China and Three Gorges area in China. The research shows some exogenic geological processes such as differential weathering, river erosion, seawater abrasion and carbonate dissolution can cause rock cavities and cantilevers on the surface of rock slopes. On the basis of field investigation, two kinds of failure modes for cantilever and tension crack-type collapse have been established. The two different failure modes are thick hard rock inter-bedded by thin weak layer and thin hard rock inter-bedded by weak layer respectively. According to the calculation theory of maximum bending stress for cantilever beam, the formulas of limit depth for rock cavity has been derived; and moreover, the time of failure of a collapse has been predicted using the rate of weather denudation for limestone. Analysis results show that the limit depth of rock cavity is positively correlated with the thickness of cantilever and negatively correlated with the depth of tension crack on the top of slope. According to the method of ratio of maximum tensile stress to tensile strength, a formula of safety factor has been deduced. Furthermore, the evaluation criteria for cantilever and tension crack-type collapses are given. Finally, the new method is verified by a typical case study; and the results show that some features such as concise formula and reliable calculation are obvious in the actual project application.