Abstract

The micromechanism of the effects of different height/width ratios (H/W) and initial stress levels on unloading characteristics of deep rock was investigated based on PFC3D true-triaxial unloading simulation. The results show that the increase of H/W will increase the movement speed of rock particles and intensify the acoustic emission (AE) activity inside the rock. With the increase of H/W, the failure mode of rock changes from splitting failure to tensile-shear failure. With increasing initial stress level, the particle velocity and overall fragmentation degree of rock increase. However, the increase of lateral stress will limit the coalescence of microfractures and weaken AE activity in the rock. Under unloading condition, the bonds between particles generally crack along the unloading direction, and the tensile effect is more pronounced under the condition of low initial stress level and high H/W. Under unloading condition, the variable energy of rock increases with increasing H/W and initial stress level, and the kinetic energy of rock particles increases with increasing H/W. The increase of initial stress level will increase the kinetic energy of rock particles when H/W is high.

Highlights

  • The instability and failure of surrounding rock caused by excavation unloading effect is a huge problem faced by deep underground engineering

  • It can be seen from the figure that the stress-strain curve obtained by simulation experienced an elastic stage, a plastic stage, and a postpeak failure stage

  • The effects of different height/width ratios (H/W) and initial stress levels on unloading characteristics of deep rock were investigated based on PFC3D true-triaxial unloading simulation

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Summary

Introduction

The instability and failure of surrounding rock caused by excavation unloading effect is a huge problem faced by deep underground engineering. The deformation and failure characteristics of rock under different stress levels are different. Xu et al [7] studied the influence of initial stress and unloading rate on the deformation and failure mechanism of Jinping marble under true-triaxial compression. Hou et al [8] examined the effects of unloading rate on the deformation and failure of surrounding rock under different confining pressures. Zhang et al and Yin et al [9, 10] performed test and numerical simulation under different stress levels to investigate the deformation and failure characteristics of rock. Li et al and Ma et al [11, 12] carried out laboratory tests and obtained the failure mode and spalling strength of rock under different confining pressures

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