Abstract: Several stable, continuous and thick incompetent beds exist in Jurassic red strata in Wanzhou. With the X-ray diffraction analysis, infrared ray analysis and scanning electron micrograph, the main mineral components and microstructures of the incompetent beds are identified. The results show that the incompetent beds are composed of montmorillonite, feldspar, ?-quartz, illite, chlorite, etc; and in which exist large amount of sheet crystals, many microfissures and micropores, a few microgrid fissures and directional crystal structures. Field investigations show that the incompetent beds were acted upon by a set of compressive tectonic forces, and shear failures occurred in some of the incompetent beds. A set of tests were conducted on the incompetent bed specimens to obtain the physico-mechanical characteristics. Test results show that the incompetent beds are medium swelling potential, and shear strength becomes very low once the incompetent beds attract water to saturation. The characteristics of the incompetent beds mentioned above prove that the incompetent beds become sliding surfaces of rock landslides easily under some special conditions.

Key words: Wanzhou, incompetent beds of red strata, mineral component, fabric and structure, physico-mechanical characteristics, rock landslide