青藏高原东南部大型岩质高速远程崩滑启动地质力学模式初探

Preliminary Analysis on Initial Failure Modes of Large Rock Avalanches’Source Slopes in the Southeastern Qinghai-Tibet Plateau

高速远程崩滑破坏性居各类崩滑之首。青藏高原东南部是中国大型高速远程崩滑最发育的地区。源区斜坡破坏是大型高速远程崩滑发生的前提,弄清源区斜坡破坏模式及其发生条件既是研究此类崩滑高速远程机理的基础,也是预防此类崩滑灾害的前提。基于青藏高原东南部15处具有不同流动特征和流通路径的大型高速远程崩滑现场调查数据、影像数据和前人资料,分析了15处崩滑源区斜坡地形地质条件、斜坡破坏模式和诱发因素。研究发现:1)源区斜坡高陡和剪出口高位是高速远程崩滑的必要条件,坡高大于150 m、坡度大于30°、剪出口高出坡底大于100 m可能是区内高速远程崩滑发生的基本地形条件;2)区内高速远程崩滑多发于花岗岩、玄武岩两类坚硬块状岩斜坡和片麻岩、变质砂岩+板岩、灰岩这3类坚硬-较坚硬层状岩斜向坡、逆向坡和陡倾顺向坡;3)斜坡破坏模式受结构面控制,具有复合楔形体滑动、不规则块体复合平面滑动、不规则块体倾倒-崩落、弯曲折断-滑移和顺层滑移-溃曲等5类破坏模式;4)崩滑受地震诱发最为普遍,冰川融水其次,自重作用下的累进性破坏也时有发生。以斜坡地质结构、破坏模式和失稳动力类型为切入点,青藏高原东南部大型高速远程崩滑源区斜坡破坏启动的地质力学分类模式可归为8类:坚硬块状岩复合楔形体高位剪出滑移模式、空隙水压浮托的坚硬块状岩复合楔形体高位剪出滑移模式、坚硬块状岩高位剪出复合平面滑移模式、较坚硬-坚硬层状岩高位剪出复合滑移模式、坚硬层状岩块体高位倾倒-崩落模式、坚硬-较坚硬层状岩高位剪出复合滑移模式、坚硬-较坚硬层状岩弯折-高位剪出滑移模式、坚硬-较坚硬层状岩平面滑移-溃曲-弹冲模式,地震抛射作用与上述模式叠加也是该区高速远程崩滑的主要特征之一。

Large rock avalanche is the most devastating landslide type in the world.The southeastern Qinghai-Tibet Plateau is one of the most susceptible areas to large rock avalanche in the world.The slope failure in source area is the premise of large-scale high-speed and long-distance landslides.It is not only the basis of studying the long-distance mechanism of such landslides,but also the premise of preventing such landslides.To explore initial failure conditions of rock avalanches in the area,source slopes’characteristics of 15 cases were analyzed with focusing on topographical and geological conditions,failure modes and trigger factors based on site investigation,satellite image analysis and unmanned aerial vehicle survey.It was found that:1)runouts of the rock avalanches depended strongly on heights of source slopes and their drop heights with minimum slope height of 150 m,drop height of 100 m and slope angle of 30°;2)rock mass prone to rock avalanches were massive granite,basalt,and bedded limestone,sandy slate,slate and gneiss,all of which were either very competent or competent rocks with brittle failure natures,and of which occurrence of bedded rocks were either steeply dip slope,obliquely dip slope or reversely dip slope;3)all of the source slopes’failure were controlled strongly by discontinuities,including dip-slope,reverse dip-slope and obliquely joints as well as bedding planes.Field observation and joint survey revealed that five kinds of initial failure modes commonly occurred in those rock avalanches’source slopes,specifically compound wedge slide,compound planar slide,flexural slide,toppling fall and buckling slide;4)although it was common that some rock avalanches occurred with no specific trigger,earthquake was primary trigger of most rock avalanches,followed by glacier melting,both of which agitated those rock avalanches’extremely rapid motion and exceptional long runout.Combining failure modes,rock mass type,slope structure,controlling discontinuities and driving forces,initial failure of rock avalanches’source slopes in southeastern Qinghai-Tibet Plateau could be categorized into different groups in terms of geomechanics,including compound wedge slide or planar slide of massive rock slopes driven by gravity or plus earthquake,or pore water pressure,compound wedge slide or planar slide of obliquely dip bedded rock slope driven by gravity or plus earthquake,toppling fall or flexural slide of reversely dip bedded rock driven by gravity or plus earthquake,and buckling slide of steeply dip slope bedding rock driven by gravity or plus earthquake.The superposition of seismic ejection and the above-mentioned model was also one of the main characteristics of high-speed and long-distance landslides in this area.