Abstract
The acoustic emission characteristics of rock specimens under different initial unloading confining pressures were tested to obtain the damage and rupture characteristics of the sandstone unloading confining pressure path. The CT scan and three‐dimensional reconstruction of the fractured rock specimens were carried out to study the differences of energy evolution and acoustic emission characteristics during the failure of sandstone under different initial unloading pressures. The results show that the unloading confining pressure has a significant influence on the deformation and failure of the rock. There is a significant yielding platform for the circumferential strain and the bulk strain at the peak of the unloading pressure. The larger the initial unloading pressure is, the greater the axial absorption strain energy, the dissipative energy, and the elastic strain energy are at the peak point. After the stress peak point, the elastic strain can be quickly converted into the dissipative energy for rock damage. The elastic energy released from the moment of rock failure under high confining pressure is more concentrated. The acoustic emission ringing and b value characteristic parameters of the rock have a good correlation with the internal energy evolution of the rock, which better reflects the progressive damage of the rock under low stress and the sudden failure of high‐stress unloading.
Highlights
During the excavation process of rock underground engineering, the excavation state is in the loading state before excavation
In terms of unloading confining pressure and cyclic loading and unloading acoustic emission test: Weizhong et al [11], through the analysis of acoustic emission characteristics of granite under unloading confinement, discussed the characteristics of acoustic emission characteristics of rock failure; Liming et al [12, 13] carried out the acoustic emission test of marbles under loading and unloading and analyzed the relationship among rock damage, rupture, and acoustic emission characteristics under the loading and unloading path; through the cyclic loading and unloading of coal specimens acoustic emission test, Jun et al [14] drew a conclusion that cyclic loading and unloading acoustic emission memory effect has advanced characteristics
From the perspective of energy conversion of rocks, the higher the rate of reversible elastic strain energy stored in the rock is, the sudden destruction of the specimen is more severe, and the shear failure of the rock specimen occurs under high confining pressure and high elastic strain energy
Summary
During the excavation process of rock underground engineering, the excavation state is in the loading state before excavation. E study on the failure law of rock damage under unloading confining pressure is of great significance for revealing the mechanical properties and fracture mechanism of rock under the unloading state. Acoustic emission as an indirect characteristic parameter is difficult to truly reflect rock internal damage evolution. It is known from the laws of thermodynamics that energy is conserved, and energy transformation is the essence of the process of material change. The author studies the mechanical properties, energy evolution, and acoustic emission characteristics of sandstone specimens under different initial unloading pressures to explore the characteristics of rock damage, combined with CT scanning and 3D image reconstruction techniques. The author studies the mechanical properties, energy evolution, and acoustic emission characteristics of sandstone specimens under different initial unloading pressures to explore the characteristics of rock damage, combined with CT scanning and 3D image reconstruction techniques. e failure mechanism and macroscopic failure morphology are analyzed to provide theoretical support for further understanding the fracture mechanism of rock materials
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