Elastoplastic Closure Characteristics of Dislocated Sandstone Fractures Subject to Normal Loads

The study of the nonlinear closure behavior of rock fractures is of great significance to the stability analysis of fractured rock masses. An elastoplastic contact model considering an elastic–plastic mixed regime was used to analyze the elastic and plastic deformation characteristics of dislocated sandstone fractures. An unmated sandstone fracture closure experiment was carried out under normal loading. The normal displacements obtained by three contact models (purely elastic model, elastoplastic model without the mixed regime, and elastoplastic model considering the mixed regime) were compared with experimental data. The results show that the stress-displacement curve calculated by the elastoplastic contact model with the mixed regime matches the experimental observation better than other contact models, indicating that the mixed regime needs to be considered during the closing process of dislocated sandstone fractures. The ratio of plastic to elastic displacement and the proportion of plastic displacement increment to elastic displacement increment gradually decrease with the increase of normal stress, illustrating that the plastic deformation of dislocated sandstone fractures may gradually decrease, and the proportion of elastic deformation could potentially rise as the normal load increases.