Incompetent beds in Jurassic red clastic rocks and relationship with landslide formation in Chongqing, China

摘要

Several incompetent beds exist in Jurassic red clastic rocks in Chongqing. With the identification of X-ray diffractometry and infrared ray analysis, the incompetent beds are mainly composed of smectite,chlorite, feldspar, quartz, and illite. The content of smectite is the key factor to effect on the characteristics of the incompetent beds. The scanning electron micrograph identifies that the microstructure of the incompetent bed appears directional structure of the clayed mineral to a certain extent, which is the result of the chorus of.up pressure and long-time shear movement. With the increasing of the clayed mineral directional structure, the shear strength of the incompetent bed is close to residual strength. The slope stability decreases along with the microstructure change of the incompetent bed. According to the physical and mechanical tests, the incompetent beds are medium to strong swelling potential and shear strength drop greatly once the incompetent beds attract water to be saturated. These characteristics indicate that the incompetent beds in red clastic rocks could develop to be the slip surface of the rock landslide easily under the special condition. It also is the most special factor to form horizontal rock landslide.