Study On Deformation Behavior Of Rough-walled Rock Fracture Subject To Normal Stress

Study of rock fracture deformation under normal stress is significant for quantitative analysis of geophysical problems and rock fracture hydrodynamics in civil engineering applications.In this study,a new numerical method of elastic-plastic contact model is proposed and verified by physical experiments of granite and fine sandstone.The curves of numerical simulation show quite good agreement with the experimental loading results.Four groups of fine sandstone with a single fracture test are staggered at different transverse distances.Four cyclic loading and unloading experiments are carried out and the corresponding loading curves are calculated by numerical simulation.The reliability of the Boussinesq's solution for the half space elastic-plastic contact model of rock fracture closure analysis is verified by high-precision and high-resolution experiments.In addition,the experimental damage area is compared with the plastic area from the numerical simulation.The analysis of the image shows that the experimental damage area is basically the same as the numerical simulation plastic deformation area,while the local experimental damage is larger than the numerical results.Based on the elastic-plastic model,,we compare the experimental stress-strain curves with the numerical simulation results of fracture closure under the normal stress for the fine sandstone,granite and coarse sandstone samples.In this study,by three-dimensional roughness(referred to Z₂^3D) and fracture surface correlation length,we can establish the relation between multi-scale surface roughness and fracture surface.The stress-displacement curves of three kinds of rock fractures are analyzed by various formulas in the process of compression and closure.The fitting results show that the classical BB model can not explain the curves of rock fracture compression,especially for the low stress condition.The unified exponential model is developed on the basis of BB model,and the results by the modified model are consistent with the numerical results.Three parameters in the fitting results(i.e.the maximum closure V_max,the initial stiffness K_ni and the coefficient n)can be related to the average aperture of the fracture,the dislocation distance of the fracture and the correlation length.The relationship between normal stiffness and normal stress is also analyzed in this study.When the displacement of upper and lower surface of rock fracture is large,the normal stiffness will eventually tend to a stable value when the stress value is high.