Study of rheological properties of rocks in experiments on stepwise loading of cylindrical samples

A method for determining the empirical dependence of the rheological properties of rocks on stresses has been developed and tested in the laboratory. The results of tests of cylindrical samples of rock salt and bischofite of the Nizhnevolzhsky deposit were used to obtain strain curves under stepwise loading and develop and verified a viscoelastic model describing the change in strains over time. It has been shown that the parameters characterizing the elasticity and the viscosity of the studied rocks decrease with increasing stress. This corresponds to the successive transition from the stage of elastic deformation to the stage of decaying, steady-state, and progressive creep. It has been established that creep of bischofite manifests itself at stresses above 0.5 MPa, and the creep of rock salt at stresses above 5 MPa. In relation to the uniaxial compressive strength and maximum strains, the creep of bischofite manifests itself at a relative strain above 0.0013 and at a relative stress of 0.19, and for rock salt, these values exceed 0.11 and 0.43, respectively.