The study on the unloading effect of rock excavation is of great significance to the stability, support and design of surrounding rock of roadway. In order to reveal the effect of different unloading timing and unloading rate on the mechanical properties of rock, the uniaxial compression servo test is used. The machine performs different single-axis unloading timings and different unloading speed tests on sandstone. The test results show that the strength and elastic modulus of the rock increase with the increase of the unloading speed under the same unloading time. At the same unloading rate, the greater the unloading timing, the greater the strength of the rock sample. When the unloading time is small, the rock rupture network is relatively developed, the rock sample is broken, and the broken rock mass is flaky. When the unloading time is large, the rock sample destruction is relatively simple, and the rock sample is less broken. At low unloading rate, the rock sample damage is more complicated. Under the high unloading rate, the rock sample damage is simple. Under the same unloading rate, the failure angle increases with the unloading time. At the same unloading timing, the failure angle of the rock sample at the high unloading rate is greater than the low unloading rate. The acoustic emission characteristics of sandstones are significantly different under different unloading timings and unloading speeds. This can provide a reference for the prediction or judgment of rock failure caused by roadway excavation.

1 Introduction

Excavation of underground engineering is a complex process of unloading, roadwayexcavation and stope mining. The instability of surrounding rock is often caused by excavation unloading caused by ground stress release and stress boundary conditions in some directions, thus Causes the surrounding rock to be caused by local damage to overall instability. Due to the heterogeneous discontinuity of the rock mass, the mechanical properties of the rock under unloading conditions are different from those under loading conditions [1]. The failure characteristics of the actual excavation are closely related to the excavation unloading timing and unloading speed, and there is still a large deformation development after excavation unloading. Therefore, the sandstones under different unloading timings and unloading rates are studied. The mechanical characteristics and acoustic emission characteristics have important theoretical significance and engineering application value for improving the quality of engineering construction, maintaining the stability of roadway surrounding rock, guiding support and design.

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