Abstract: To research the influencing factors of shearing properties and the micro-evolution mechanism of shear failure, we carried out direct shearing numerical experiments. On the bedding planes between silty mudstone and marlite in Badong formation using particle flow software based on wall rock’s micro-parameters determined by laboratory experiment results. The research results are as follows the shearing curve of bedding planes between two different rock types in Badong formation is between silty mudstone and marlite isotropic planes; the shearing mechanical properties of bedding planes between two different rock types are influenced by the surface morphology, normal stress and the wall rock combination. In addition, the shear failure evolution process of bedding planes between two different rock types is influenced by the surface morphology. The shear failure of zigzag bedding planes between two different rock types develops mainly along the weak wall rock gradually from both sides to the middle. The shear failure of flat bedding planes between two different rock types evolves evenly along one side of the weak wall rock. Based on the results, an expression is given to describe the relationship among the ratio of shearing strength of bedding planes of two different rock types to that of normal joint in soft rock, the rock combination coefficient, and the normal stress. It’s concluded that inter formational sliding of bedding planes between two different rock types in Badong formation is an important factor that leads to the rock mass failure of this stratum.

Key words: rock mechanics, Badong formation, bedding planes between two different rock types, shearing mechanical properties, evolution mechanism, PFC