Abstract
The triaxial cyclic loading and unloading test was carried out on a TAW-2000 rock mechanics to study the permeability characteristics of deep-buried sandstone. This paper analyzed the evolution laws of permeability, elastic modulus, rock damage, dissipated energy, and acoustic emission events of sandstone under different confining pressures. It also introduced the concept of relative strain and further discussed the relationship between relative strain and permeability. The test results showed that the permeability of sandstone under cyclic loading and unloading obviously experienced three stages. At a low strain level, the damage degree of sandstone was low. As a result, both the number of acoustic emission events and the proportion of the dissipated energy density were small. In this stage, with increasing the stress, the permeability decreased. With the increase of the relative strain, the propagation of fissure increased through rock interior and the damage of rock was accumulated. Consequently, the number of acoustic emission events grew slowly, and the proportion of dissipated energy density and the damage variable (D) increased gradually. In this stage, the permeability increases. As the axial strain reached the peak strain, the fissures developed into cracks and the rock failure happened. The number of acoustic emission events increased rapidly; both the proportion of the dissipated energy density and the damage variable (D) obtain the maximum value. In this stage, the permeability increased greatly. In this study, the point of fissure propagation of rock specimens was used as the point of demarcation. Before the fissures propagated, the permeability increased slowly and it was in accordance with a linear function. After the fissures propagated, the degree of rock damage increased, and the permeability increased in the form of an exponential function. The larger the confining pressure was, the smaller the relative strain corresponding to the point of fissure propagation was.
Highlights
China is rich in coal resources with the characteristics of the various covered depth of the coal seams
Based on the experimental data from the cyclic loading and unloading test on sandstone under different confining pressures, this paper analyzed the evolutionary relationship between permeability and relative strain, damage, energy density characteristics, and acoustic emission characteristics
Damage coefficient, energy density characteristics, and acoustic emission characteristics can effectively describe the evolution of permeability with rock damage
Summary
China is rich in coal resources with the characteristics of the various covered depth of the coal seams. Peng et al [14] analyzed the energy mechanism of the evolutionary process of damage of coal and rock mass under various confining pressures and concluded that the energy dissipation of damage increases with the increase of cyclic stress. Wang et al [21] conducted cyclic loading and unloading tests on deep coal and rock masses under confining pressure obtained the permeability of coal and rock mass and established its relationship with various mechanical properties of coal and rock mass. Erefore, taking into account the strong disturbance caused by mining activities, this paper will study the permeability of deep rocks under different confining pressures through the permeability test of cyclic loading and unloading In most cases, mainly focused on the shallow coal and rock mass under cyclic loading and unloading. ere is a lack of analysis of permeability characteristics of coal and rock mass with multiparameters in the deep. e coal stratum in the deep coal mine is mainly sandstone. erefore, taking into account the strong disturbance caused by mining activities, this paper will study the permeability of deep rocks under different confining pressures through the permeability test of cyclic loading and unloading
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