三峡库区万州安乐寺滑坡滑带特征

Slip Zone Characteristics of Anlesi Landslide in Wanzhou of Three Gorges Reservoir Area

安乐寺滑坡是三峡库区典型的缓倾角红层基岩滑坡,对其滑带特征进行详细的研究有助于揭示缓倾角红层基岩滑坡的形成机制.宏观地质特征显示,安乐寺滑坡滑带是侏罗系红层中灰白色泥岩(软弱夹层)经挤压滑动所形成的,擦痕指示最后一次滑动方向为100°.通过X射线衍射分析和红外光谱分析表明,安乐寺滑坡滑带主要矿物成分为蒙脱石、伊利石、长石、石英等;其特点是蒙脱石含量高,并且滑动面上的蒙脱石含量高于滑带的蒙脱石含量.经扫描电镜观察,滑带土微观结构以片状结构与定向排列结构为主;显微擦痕发育,并指示滑带曾发生过多次滑动.对滑带土的物理力学性质进行实验研究可知:滑带土为中等膨胀性粉质粘土,其抗剪强度低;且吸水膨胀后,抗剪强度大大降低.滑带土的这些特殊性质,为安乐寺滑坡的滑动提供了物质基础.

Anlesi landslide is a typical gentle-dip landslide forming in the red clastic rocks in the Three Gorges Reservoir area. In order to discover the mechanism of the gentle-dip landslides forming in the red clastic rocks, the slip zone characteristics of Anlesi landslide were studied in detail in this paper. Field investigations show that the slip zone of Anlesi landslide was formed from a white mudstone （an incompetent bed） in Jurassic red strata by extrusion stress. The direction of the striations on the sliding surface indicates that the latest sliding direction of the landslide is 100°. The X-ray diffraction and infrared ray analysis reveal that the main mineral components of the slip zone are montmorillonite, illite, feldspar and quartz, et al.. The significant character is that the slip zone contains a large amount of montmorillonite, and the sliding surface contains more montmorillonite than the slip zone does. The results of scanning electron micrograph display that the microstructures of the slip zone are mainly sheet crystals and directional crystal structures, and micro striations developed well. A set of tests were conducted on the slip zone specimens to obtain the physico-mechanical characteristics. Test results show that the slip zone is medium swelling potential slity clay, and shear strength becomes very low once the slip zone absorbs water to saturation. The characteristics of the slip zone mentioned above make it possible to discover the mechanism of the gentle-dip landslides forming in the red clastic rocks.