Study on Permeability of Deep‐Buried Sandstone under Triaxial Cyclic Loads

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.

Comprehensive review of geomechanics of underground hydrogen storage in depleted reservoirs and salt caverns

“…Similar experiments on sandstone rocks reveal a strong correlation between the strain accumulated in each cycle and the resulting change of permeability and after 30 cycles, the permeability change becomes negligible as the strain stabilises [91]. Those irreversible changes in permeability are shown to be more pronounced for reservoirs of low permeability [92,93,94,95,96]. Low-and high-frequency oscillation-based creep experiments of pore pressure in sandstones concluded that even a significant monotonic increase in pore pressure has a minor effect on the mechanical properties of the rock [97].…”

Experimental Study on Pore Structure Evolution of Unloaded Rock Mass during Excavation of Reservoir Slope under Dry–Wet Cycle

“…Most of them start from the triaxial unloading test to study the crack evolution and failure mechanism, mechanical parameter damage degradation effect, and strength characteristics of various rocks during unloading [3][4][5][6]. Considering the influence of unloading rate on rock failure mode, triaxial unloading tests under different unloading rates were designed and carried out to analyze the failure characteristics of rock [7][8][9][10]. On this basis, many scholars intervened in the influence of various unloading paths and studied the energy evolution characteristics of rock in triaxial unloading failure processes from macro and meso perspectives [11][12][13].…”

Study on strength characteristics and permeability of chlorite schist during triaxial compression permeability

“…With the continuous development of human beings to the depth in the process of underground engineering development and construction, especially the mining depth of underground mineral resources has reached more than 1000 meters, the engineering problems encountered are becoming more and more complex and have great particularity compared with surface engineering. The seepage and stress caused by engineering excavation are the key factors affecting coal mine safety production, and the water gushing caused by high underground water pressure is the potential danger of mining activities [1][2][3][4]. Among them, the serious deformation and damage of roadway (tunnel), especially the prominent phenomenon of floor heave is a more common engineering problem.…”