Experimental study of deformation and acoustic emission characteristics of rectangular roadway under different unloading rates

Under fast and slow excavation unloading rates, experiments were carried out on the surrounding rock specimens of the cement mortar to study the deformation law and acoustic emission characteristics of the rectangular roadway. The strain characteristics of surrounding rock and the evolution characteristics of AE impact count, energy and spectrum were obtained in this study. The test results showed that under rapid unloading, the strain release rate was high, and the deformation was unstable after unloading. However, under slow unloading, the surrounding rock stress was fully adjusted, which was conducive to the full release of strain, and the deformation developed relatively stable after unloading. Under the two unloading modes, the surrounding rock of the roof and the gang in the rectangular roadway were mainly subjected to the radial tensile deformation, while the surrounding rock of the corner mainly experienced the tangential compression deformation. As the depth of the surrounding rock increased, the unloading effect gradually decreased. The AE impact count and energy evolution characteristics of the two unloading rates were well correlated with the strain characteristics, revealing the development process of cracks and damages in the surrounding rock under excavation unloading. The precursor information of the main rupture of the surrounding rock can be referred to the increases of the width of peak frequency band and the number of the peak frequency of the high amplitude signal in a certain frequency band. Under rapid unloading, large pieces of flaking occurred around the roof and the gang. Under slow unloading, the through cracks perpendicular to the corners were generated at intervals around the roof and the gang, and the roof and the gang swelled obviously but didn't fall off. The damage of the right-angle rock was small in these two states.