甘肃永靖黑方台地区灌溉诱发型滑坡发育特征及力学机制

摘要

水是诱发黄土滑坡最为积极的因素,以灌溉诱发型滑坡尤为典型.基于野外水工环地质综合调查,对黑方台地区灌溉渗透诱发滑坡的发育特征进行总结.通过分析特定孕灾地质条件下滑坡发育特征的差异,认为黄土滑坡形成的力学机制以滑移-压致拉裂-剪断型和蠕滑-拉裂-滑移型为主,而黄土-基岩滑坡以滑移-压致-拉裂型为主.滑移-压致拉裂-剪断型黄土滑坡为原位溯源后退扩展式,系灌溉水入渗后造成黄土饱和带厚度增大,不仅造成台缘周边地下水溢出带部位渗透压力增大,且抗剪强度显著弱化,从而在坡体自重作用下发生蠕滑剪切.锁固段突然破坏使滑坡快速启动,滑体冲击致早期饱水滑床产生液化,产生高位抛射,借助原始地形滑体加速运移形成高速远程运动.蠕滑-拉裂-滑移型黄土滑坡是黄土底部饱和带厚度较薄或灌溉入渗影响较小的地段,以后缘拉裂为主激发形成.渗灌溉水长期入渗造成下伏基岩顺倾泥岩层面软化泥化,从而在顺向坡段产生黄土-基岩顺层滑坡,该类滑坡以低速短程滑坡为主.%Loess shows intensive water sensitivity,and hence water becomes the most positive factor triggering loess landslides,of which irrigation-induced landslides are most typical.Based on field geological survey,this paper summarized the development features of irrigation-induced landslides in Heifangtai.According to an analysis of the development conditions and development features of different types of landslides,the authors hold that the mechanical mechanisms of loess landslides mainly include sliding-compression-induced tension crack-snipping and creep-tension crack-shding,while the mechanism for loess-bedrock landslides is mainly slidingcompression-induced tension crack-snipping.Loess landslides start with the increase of thickness of saturated loess layer after infiltration of irrigation water.The water content of unsaturated loess differs from that of saturated loess,and therefore shear strength of loess is weakened.Furthermore,the increase of groundwater table due to long-term irrigation leads to the increase of the seepage force at the edge of the plateau where groundwater discharges.So the slopes start to creep and shear under self-weight,and landslides are initiated.Irrigation-induced loess landslides are characterized mainly by high speed and long run-out.Infiltration of irrigation water leads to the softening of the outward dipping structural surfaces in the underlying bedrocks.Hence loess-bedrock landslides are initiated on slopes with outward dipping structural surfaces.Due to large fiictional forces on the main sliding surfaces of mudstones,the strain energy accumulated in the process of the formation of sliding surfaces is released in the form of slow continuous creeps of plastic deformation.Thus loess-bedrock landslides are mainly of low speed and short run-out type.