Deformation and Energy Dissipation Characteristics of Joints Under Cyclic Confinements

Using the rock testing system, MTS-815, we conducted cyclic-confinement loading tests on the joints, made of Maokou Limestone. Then, by analyzing the characteristics of the confinement-normal displacement curve of the joints with various roughness coefficients, initial openings and confinements, we investigated the energy dissipation law of the plastic hysteresis loop, the elastic–plastic law and the stiffness characteristics of the joints. The results show that the increase in the confinement cycle shrunk the area of the plastic hysteresis loop; whereas the increase in the roughness of the joint surfaces enlarged the area, and further promoted the dissipated energy. In addition, plastic deformation and elastic deformation subsequently occurred on the joint with the increase in the confinement cycle. Moreover, the increase in the confinement cycle promoted the normal stiffness. According to the characteristics of the normal deformation, an index, β, was introduced to modify the power function model for the normal stiffness of the joint after specific loading cycles. The fitted curves, obtained from the modified model, agree well with the laboratory curves.