Experimental Study on Seepage and Fracture Characteristics of Cemented Rock Samples under Triaxial Stress

Abstract

To study the seepage and fracture characteristics of cemented rock strata, a series of triaxial seepage tests on cemented rock samples under different confining pressures and water pressures were carried out in this study. The triaxial strength, elastic modulus, volume strain, and the permeability of the cemented rock samples were analyzed by the seepage unit connection probability model and Kozeny-Carman model. Based on test results, the stress state of cemented rock samples was divided into four stages: nonlinear compaction stage, linear elastic stage, stress yield stage, and failure and postfailure stage. The triaxial strength of the cemented rock samples gradually increased with the increase of confining pressure but decreased with the increase of water pressure. The elastic modulus of the cemented rock sample increased with the increase of confining pressure but decreased with the increase of water pressure. Besides, the volume strain of the cemented rock sample was analyzed, and the volume strain change of the cemented rock sample was also classified into three stages: the increasing stage of crack volume strain, the stable stage of crack volume strain, and the decreasing stage of crack volume strain. Based on the results of triaxial seepage tests, the evolution of permeability was divided into the declining stage, increasing stage, and redescend stage. Through the seepage unit connection probability model and Kozeny-Carman model, the evolution of crack volume was obtained, and the evolution of crack volume with axial strain was also classified into three stages: the original pore closure stage, crack network expansion stage, and crack network closure stage. The permeability evolution and the crack volume evolution were also compared. The comparison results suggest that three stages of crack volume evolution are all ahead of three stages of permeability evolution, verifying that the crack propagation induces the formation of seepage channels in cemented rock samples. This research will provide a valuable reference for the study of instability and water inrush mechanism in cemented rock strata.