鄂西清江偏山滑坡群易滑地层特性

二叠系大隆组和三叠系大冶组是清江流域碳酸盐岩区的易滑地层,清江中游的偏山滑坡群即为典型实例,夹泥的大冶组泥灰岩及大隆组顶部泥岩形成了滑体下部与滑带。通过现场调查、取样和室内测试,对两者的矿物和化学成分、力学性质等进行了研究分析。结果表明:大隆组顶部泥岩含胀缩性明显的蒙脱石,黏土矿物总含量为40%～75%,泥岩泥化后强度明显降低且表现出典型蠕变特性,通过流变实验得到其长期强度指标黏聚力为23kPa,摩擦角18.1; 大冶组下部泥灰岩含泥量较高,层间黏土矿物主要为伊利石和绿泥石,层面水平,顺层错动导致泥灰岩表面磨蚀及层间黏土矿物定向排列,特别是浸水后结构面强度降低明显形成易滑面加剧滑坡体的变形; 滑坡演化与清江发育之间具有相互促进作用,类似地质结构和水往复作用地带岸坡需特别重视。

FEATURES OF SLIPPERY STRATA FOR PIANSHAN LANDSLIDES IN QINGJIANG RIVER CATCHMENT OF WESTERN HUBEI PROVINCE

The Dalong formation of Permain and the Daye formation of Triassic are the main slippery strata in Qingjiang River catchment of western Hubei province. Pianshan landslide is a typical example. Its lower part is composed of thin-bed limestone of Daye formation. Its slide belt is formed with mudstone or shale of the top of Dalong formation. Depending on field investigation, sampling and mechanical tests in laboratory, following results on the mineral and chemical compositions and mechanical properties are obtained for the two formation materials. The main clay mineral in the mudstone is montmorillonite with good swelling and shrinkage character. The content of clay minerals is 40%～75%.The strength of the mudstone decreases obviously after argillization, companying with typical creep deformation. For long term strength properties, the cohesion is 23kPa and the internal friction angle is 18.1,which are achieved with rheological tests. The amount of clay minerals in the thin bed limestone is high. The main components are illite and chlorite and the bedding surfaces are very smooth. The surfaces are abraded and the clay is oriented between the layers due to the bedding slipping deformation. The strength of interlayers decreases obviously and forms the slide surface inside the landslide body when the layers are saturated. There are good mutual effect and acceleration between the landslide evolution and Qingjiang River development. The similar geological structure and water reciprocating strip should be taken seriously.