Abstract:The strength experimental investigations on layered mud rock mass have been conducted. For the two basic situations where the crack is vertical to layered rock mass and parallel to layers,the experimental studies on crack fracture initiation in the layered rock mass have been carried out. Due to the obvious orthogonal aeolotropy in strength,the layered rock mass displays obvious particularities in crack fracture initiation,for example,the shear expanding in pure model I and mixed model I–II crack tips,winding propagation routes. In addition,the fracture mechanism has been analyzed using fracture mechanics and finite element method. The critical fracture curve when cracks are vertical to the layered rock mass has also been obtained by using numerical values KI and KII. The experimental research and the theoretical discussion may provide a foundation for the usual situation analysis when cracks are inclined to layered rock mass. The results and the critical fracture curve can provide references to layered rock mass slope projects.