Slip zone characteristics of Anlesi landslide in Wanzhou of Three Gorges Reservoir area

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.