Quantitative damage, fracture mechanism and velocity structure tomography of sandstone under uniaxial load based on acoustic emission monitoring technology

Abstract

Rock is an opaque medium body, and it is impossible to visually see its internal damage, which brings difficulties to the investigation of rock damage. In the light of the problems of rock damage, fracture mechanism and velocity structure evolution under load, the acoustic emission (AE) technology is adopted in this paper to monitor and analyze AE events in sandstone specimens during uniaxial loading. To investigate the damage law and fracture mechanism of sandstone under uniaxial load, a mechanical model that can quantitatively describe rock damage is constructed. Finally, the time-lapse double-difference tomography (tomo-TDD) is used to invert the velocity structure in the loaded rock. The results show that the fracture mode of the sandstone under uniaxial load is mainly shear fracture accompanied by a small amount of tensile fracture. The fracture modes of the three stages divided by the characteristics of AE signals, during loading process of the sandstone, is shear fracture, tensile fracture and shear fracture respectively. The damage mechanics model including the whole process of stress-strain curve in the post peak stress stage and the stage of primary micro-pores’ compaction and closure can quantitatively describe the damage degree and accurately predict the failure of rock under different stress levels, which is consistent with the velocity structure inverted by tomo-TDD. The velocity structure inversion based on tomo-TDD can reflect the damage degree, damage distribution and velocity structure evolution of any section under any stress level. The research results can be used for rock stability analysis and risk prediction, and at the same time, it provides a more intuitive reference for the non-destructive testing of rock masses in engineering.