Abstract
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.
Highlights
The fault zone is a common geological structure in coal mining activities, and the broken rocks in the fault zone are generally in a weakly cemented state [1, 2]
Test results show that the triaxial strength of the cemented rock samples gradually increases with the increase of the confining pressure but decreases with the increase of the water pressure
The confining pressure and water pressure have no obvious effect on the Poisson ratio of the cemented rock sample
Summary
The fault zone is a common geological structure in coal mining activities, and the broken rocks in the fault zone are generally in a weakly cemented state [1, 2]. The results show that the permeability coefficient peak value appears before the stress peak value, and the filling cracked rock is sensitive to the variation of confining pressure These researches cannot directly reveal the disaster-causing mechanism of water inrush in the surrounding rock of the fault. Zhu et al [24] studied the permeability evolution mechanism of fractured rock mass with the fillings and proposed the permeability model of fractured rock based on the volume strain, which can well verify the test results of true triaxial seepage. The triaxial seepage tests were carried out on cemented rock samples, and the instability of the surrounding rock in fault was simulated under threedimensional in situ stress. The mechanical and hydraulic properties of cemented rock samples were analyzed under
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