Nonlinear deformation effect of unloading rate on hard rock under different confining pressures

Abstract

In this paper, triaxial loading and unloading tests under different loading and unloading conditions are carried out to explore the deformation and failure characteristics of hard rock marble, and the acoustic emission (AE) information of the test process is monitored synchronously to obtain the AE distribution characteristics. The test results show that: (1) when the unloading rate of confining pressure is small, the yield of rock is more obvious, the failure peak value is higher, and the Poisson effect is more obvious under loading and unloading, while when the unloading rate is larger, it shows multi-stage failure; (2) there is a linear relationship between strain deflection stress compliance and unloading rate. With the increase of unloading rate, the circumferential and volumetric compliance increases and the axial compliance decreases; (3) the smaller the unloading rate is, the greater the confining pressure is, and a large number of tensile microcracks in the main shear plane of rock form a shear zone, while the higher the unloading rate is, the smaller the confining pressure is, and the main shear plane runs through; (4) AE counts can characterize the damage degree of marble during loading and unloading. When the confining pressure is low, the damage peak of AE signals increases sharply, and the overall damage increases with the increase of unloading rate, and when the confining pressure is high, AE signals increases gradually. The overall damage decreases with the increase of unloading rate, and a “pre-peak to post-peak” lag effect can occur in the general rock failure.