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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。
The cantilever-pull-type collapse is one of the more common types of collapse, often developed in the steep rocky slope near the horizontal strata. In the southwestern and northwestern mountainous areas of China and the Three Gorges reservoir area, And collapse occurs frequently. The investigation shows that the effects of differential weathering and denudation, river lateral erosion, seawater erosion and carbonate erosion are external dynamic geologic effects of concave rock cavities and protruding cantilevers on rock slope. Based on the investigation, the collapse failure modes of two kinds of cantilever beams are summarized. According to the calculation theory of maximum bending stress of cantilever, the calculation formula of limit depth of cavity is deduced. Combined with the rock weathering and erosion rate, the time of damage of dangerous rock mass of cantilever is predicted. Based on the analysis of the calculation formula of ultimate depth of rock cavity and the field investigation of cantilever collapse, it is shown that the limit depth of rock cavity is positively related to the thickness of cantilever body and negatively related to the depth ratio of top crack. According to the maximum tensile stress - tensile ratio analysis method, the calculation formula of the stability coefficient of rock mass with cantilever failure is deduced, and the evaluation criteria of its stability are given. Through a typical example, the correctness of the method in the paper is tested, the results show that the method has the advantages of simple formula and reliable calculation.