Shear Behavior of Soil–Rock Mixture Composed of Diorite-Porphyrite Considering Weathering Sequence

Abstract

Due to the weathering process, diorite-porphyrite dikes break up into a soil–rock mixture (SRM), which is crucial to the stability of dams and reservoirs that are under frequent fluctuations of water level. However, the grain transformation and mechanical behavior of SRM during weathering have rarely been studied. This study aims to investigate the effect of dominant grain size and content on the shear properties of SRM. Therefore, a sequence that simulates the change in dominant particle size and content during the weathering process will be proposed and a series of direct shear tests will be performed on the SRM samples and two-dimensional commercial discrete element method (DEM) program particle flow code (PFC2D) numerical models. The results show that the relationship between the shear stress and shear displacement of the SRM can be expressed by an exponential function. The shear strength and internal friction angle continued to decrease with weathering and the cohesion increased slightly. By comparing the particle flow code (PFC) simulation with the laboratory tests, the shear strength of the SRM was mainly affected by the force of friction between grains. The cohesion between particles was weak and was not a significant factor that affected shear strength.