Study on mechanical properties and acoustic emission characteristics of mudstone-clay composites under uniaxial compression

In the western mining area of China, mudstone-clay composite roofs are commonly found in coal seam roadway. This kind of roadway surrounding rock has poor self-stabilization ability and is difficult to support. Therefore, through a series of uniaxial loading and acoustic emission (AE) experiment, this study explores the mechanical properties of mudstone-clay composites (MCCs) considering different thickness, horizon, quantity, and moisture content of clay layers. The research results show that: First, if the clay meets water, the bearing and deformation resistance of the MCCs are significantly weakened. The thicker the clay layer and the more quantity, the smaller uniaxial compressive strength and elastic modulus of MCCs. Second, the AE energy characteristics in different combinations of specimens are disparate. For the MCCs with hydrous clay and thicker mudstone, the AE energy peaks mostly appear at the beginning and end of the stress step in the post-peak stage. Third, the moisture state of the clay layers significantly influences the MCCs' failure mode and crack type. If the clay is exposed to water, the failure mode of MCCs changes from tension-shear joint failure to single tension failure. Finally, the tearing effect of clay lateral displacement on mudstone is dominant to mudstone cracking. The bonding effect of clay prompts the rock blocks on both sides of the mudstone fissures and clay layer form a triangular structure. In the post-peak stage, the periodic instability and rebalance of the triangular structure lead to a stepped decline in the stressstrain curves of the MCCs.