Abstract: As a common fracture model in the rock slope, the gentle dip fracture system is significant in geological engineering for slope evolution and stability evaluation. In this paper, based on the characteristics of stress field, the rock shear tests were carried out by applying the particle flow program, revealing the formation and evolution mechanism and impact factors of the gentle dip rupture system in the slope. The results show that: (1) the gentle dip angle system in the rock slope is a set of Riddle low angle shear rupture system, which consists of high-order sub-sexual geese fractures and low-order sub-conjugate shear fractures; (2) the evolution of the fracture with a gentle dip angle can be divided into several stages, showing that the propagation of the fracture system firstly occurs at a set of echelon rupture and then the conjugate shear cracks of the low order begins to expand and connects with original echelon ruptures; (3) the crack coalescence mode is different under different confining stress. The crack develops along the tips of the echelon rupture and finally links under a low confining stress, and it develops through the middle part of the original rupture under a moderate confining stress, and the coalescence will occur through a new set of echelon ruptures in the high confining stress; (4) the morphology of the rupture surface in the rock after the shear tests is closely related to the confining pressure, showing that the rupture surface is flat but the roughness is large under the medium and low confining pressure; under high confining pressure, however, the fracture presents curved surface, and it is smooth but the roughness is small.

Key words: rock slope, gentle angle rupture, evolution mechanism, mechanism mode