近水平层状砂泥岩互层边坡悬臂梁崩塌机理研究--以志丹县牛沟川河流塌岸为例

志丹县的河流岸坡常表现为坡脚泥岩凹进、坡体砂岩凸出的悬臂梁形式,崩塌灾害时有发生。以志丹县“牛沟川河流塌岸”为对象,研究了近水平层状砂泥岩互层边坡悬臂梁崩塌的破坏机理。经现场调查,塌岸边坡破坏类型为悬臂梁式崩塌,悬臂梁危岩体的主要成因为河流的长期侧向侵蚀作用及砂泥岩互层的长期差异风化作用;在现场调查基础上,考虑自重、降水以及外部荷载作用,建立悬臂梁边坡数学-力学模型,利用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和稳定性系数公式,其验算结果与野外调查一致;建立悬臂梁岸坡数值模型,利用离散元数值模拟软件UDEC,分析并总结出悬臂梁崩塌的灾变过程为:悬臂形成-裂隙产生-裂隙贯通-悬臂折断,堆积坡脚。

Failure Mechanism of Cantilever Beam in Near-Horizontal Layered Sand-Mudstone Interbedded Slope--A Case Study in Niugouchuan River Bank Collapse

The river bank in Zhidan County,Shanxi Province,is often geomorphologically characterized by lower concave mudstone and upper convex sandstone,with frequent bank collapses.Focusing on the Niugouchuan River bank collapse in Zhidan County,we further studied the collapse mechanism of the near-horizontal layered sand-mudstone interbedded slope.Field investigations show that the failure type of this bank slope was cantilever beam collapse,and the main formation reasons were the long-term lateral erosion of the river and the long-term differential weathering of the interbedded sand-mudstone;On the basis of in-situ investigation,this study established a cantilever beam slope mathematical-mechanical model considering the factors of self-weight,precipitation and external load condition.The maximum bending stress calculation theory of the cantilever beam was used to derive the formula for calculating the ultimate depth of rock cavity and the stability coefficient formula.The verification results were consistent with the field survey;By building numerical model of cantilever beam bank slope and using discrete element numerical simulation(UDEC),we analyzed and summarized the catastrophic process of cantilever beam collapse:cantilever formation-crack generation-crack penetration-cantilever breakage,piling slope foot.