Abstract
Deep high-stress roadway excavation under unloading disturbance inevitably leads to damage deterioration of the surrounding rock, which poses a serious threat to its stability. To explore the energy characteristics of white sandstone damaged by peak front unloading, uniaxial compression tests were conducted on damaged rock samples. The results show that the peak strength and modulus of elasticity of the rock sample gradually decrease with increasing damage degrees. The external work input energy, releasable elastic strain energy and dissipation energy all decreased with increasing damage. Damage evolution curves and equations of the rock samples were obtained based on the damage instantiation model established by the principle of energy dissipation and release. The effects of unloading damage on the fracture characteristics of the rock samples were analysed from both macro and microscopic viewpoints, and the results showed that a micro fracture in the rock is transformed from brittle–ductile damage, while macroscopic damage occurs in the form of a "shear"-"splitting"-"mixed shear-splitting" damage process. This paper has certain research and reference value for understanding the damage evolution characteristics of rocks with peak front unloading damage.
Highlights
The abovementioned research did not consider that the surrounding rock in the fractured zone on the surface of the deep shaft tunnel is in a low surrounding pressure state, and the energy characteristics during uniaxial stress reloading of the rock in the fractured zone by the increase and transfer of peak stress formation during the recovery process have not been studied
The mechanical and energetic properties of white sandstone samples damaged by peak front unloading are investigated through uniaxial compression reloading tests
The damage evolution equation is based on the evolution of the total input energy and dissipation energy at the peak strength
Summary
The theoretical damage evolution equation can show the evolution of damage during the recarrying process of the white sandstone test specimen after the peak, and Fig. 15 shows that the rock sample is removed before the peak is removed, resulting in internal generation of the test specimen Mechanical behaviour such as many microporous closures and internal structural surface slip friction consumes a large amount of energy, accelerating the damage to rock samples, which is consistent with the previous conclusions. When the white sandstone specimen σul = 60% is unloaded, destruction of the sample in the form of single bevel shear failure occurs, a test specimen occurs throughout the main crack from top to bottom, and the fracture angle is 68°, while several new cracks at the bottom are not obvious. With the increase of the degree of damage before the unloading peak due to internal white sandstone specimens unloading producing significant local defects, rebearing process, local defects gradually expanded, and the shear surface formed was weak, eventually leading to shear failure. This study has certain theoretical reference value for engineering practice, and the location, form, and expansion direction of the internal microcracks of rock samples require further research
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