Abstract
Understanding the damage evolution characteristics of rock material is essential to the long‐term stability and safety analysis of the underground facility. In this study, a series of cyclic loading tests under tensile or compressive stresses are conducted to investigate the damage evolution, deformation, peak strength, and failure pattern of rock salt. A special attention is paid on the microcracking process by using a 3D acoustic emission (AE) test system. The laboratory tests show that the damage degree of rock salt under compression is the highest, followed by the damage in the direct tensile test. The lowest value of damage is determined by using the Brazilian test. The damage degrees where the damage rate starts to decrease are about 0.83 in the direct tensile test, about 0.75 in the Brazilian test, and about 0.91 in the compression test. The failure mode of rock salt changes from the tensile mode in the uniaxial compression test to the compression‐shear mode in the confined compression test at low confinement. But from the confining pressure of 15 MPa, the rock salt displays great plastic dilatant distortion and without appreciable macroscopic fractures. Accordingly, with increasing confining pressure, the positions where the rapid increase in cumulative AE counts occurs and where the AE event with high energy appears are changed, from the beginning of the test at low confinement to the postpeak stage of the test at high confinement.
Highlights
Because of the extremely low permeability [1, 2], excellent ductility [3, 4], good self-healing characteristics, and rheological response under stress [5,6,7], rock salt formations are commonly used as the geologic host rock for underground storage of natural gas, oil, petroleum, and compressed air and disposal of radioactive and other chemical wastes
In the triaxial compression test on rock salt, there will be large compressive deformation in axial direction, especially when the confining pressure is higher than 15 MPa [34]. e increase in the cross-sectional area is apparent. erefore, the logarithmic strain is used in this study to describe the variation of strain of rock salt in the triaxial stress state
In the uniaxial compression test, many acoustic emission (AE) events are detected under low stress, which can be attributed to the closure of the intrinsic microcracks inside the specimen
Summary
Because of the extremely low permeability [1, 2], excellent ductility [3, 4], good self-healing characteristics, and rheological response under stress [5,6,7], rock salt formations are commonly used as the geologic host rock for underground storage of natural gas, oil, petroleum, and compressed air and disposal of radioactive and other chemical wastes. Guo et al [11] studied the mechanical properties of Jintan mine rock salt under complex stress paths based on a series of laboratory tests, including uniaxial compression, triaxial compression, unloading confining pressure, and cyclic loading tests. A series of cyclic loading tests under tensile or compressive stresses are conducted using the MTS815 rock mechanics test system. The loading is controlled by the axial LVDT displacement rate, which is 0.01 mm/min at the beginning of the test and decreased to 0.001 mm/min when the increasing stress is about 80% of the experiential peak strength of rock salt. E triaxial compression test is performed with a stress control mode, at a constant loading rate of 3 MPa/min for confining pressure and 30 kN/min for axial force.
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