Experimental Study on the Mechanical Behavior and Energy Evolution of Rock Joints During the Cyclic Loading-Unloading Shear Process

Abstract

Natural rock masses are usually highly jointed, and joints have great impacts on the strength and failure mode of rock masses. Meanwhile, the joints are subject to frequent loading and unloading under complex geological and engineering conditions. To study the evolution of mechanical behavior during this process, cyclic loading-unloading shear tests were conducted on the joint samples with the same JRC in this article and validated the proposed constitutive model. Explore the evolution law of parameters such as stiffness, energy evolution, and shear dilatation angle of the same joint surface during cyclic shear loading and unloading. The constitutive model has good applicability and the evolution of mechanical parameters is closely related to plastic shear displacement. The shear stiffness decreases gradually with the increase of shear displacement, the greater normal stress would induce greater shear stiffness. During the shearing process, the shear dilatation would be more obvious under the small normal stress. The dilatancy angle decreases rapidly at first and then tends to be flat with the increasing plastic shear displacement under the same normal stress. The energy evolution during the shear process is closely related to the shear displacement, and the cumulative dissipation energy and damping ratio reach the peak at the peak shear strength. When the normal stress is the same and the shear displacement gradually increases, the cumulative dissipation energy rapidly increases and reaches the peak, then decreases gradually to be stable. The damping ratio also increases originally and then decreases with the increasing shear displacement, with the same changing trend of the cumulative dissipation energy. Additionally, the greater the normal stress, the more energy dissipated in the shear process.

Keywords: Constitutive model, Shear stiffness, Dilatancy angle, Cumulative dissipation energy, Damping ratio