Experimental study on damage and fracture characteristics of sandstone under graded stress disturbance based on confining pressure factor
Due to frequent stress disturbances caused by mining activities,the stability of surrounding rock in underground engineering is becoming increasingly prominent,which seriously restricts the safe and efficient mining of underground mineral resources.In order to explore the damage and fracture mechanism of rock mass in the process of stress disturbance under different buried depths,based on conventional triaxial tests,graded stress disturbance laboratory tests under four groups of confining pressures were carried out in this paper.Based on mechanical analysis,acoustic emission(AE)source phased location and evolution characteristics of damage evaluation indexes,the rock mechanics damage degradation law and meso-crack development characteristics under graded stress disturbance were determined,and the correlation among rock damage state,meso-crack development characteristics and the change of damage evaluation indexes was established.The results show that:(1)The peak strength and peak axial strain of rock increase with the increase of the confining pressure under the disturbance of graded stress.The axial strain increment of stress disturbance in each stage shows a slight fluctuation in the early stage,a slow increase in the middle stage,and a rapid increase in the late stage.The average elastic modulus increases slightly at the beginning and then decreases rapidly.(2)The confining pressure reduces rock damage accumulation rate by limiting crack propagation.The rock can withstand more stress disturbances under high confining pressure,and the creep characteristics of constant pressure stage are more obvious.(3)In the early stage of loading,the crack development in the rock is only the repeated compaction failure in the damaged area and the development of a few microcracks in adjacent areas.In the late stage of disturbance,with the increase of axial force,the limiting effect of confining pressure will be weakened,resulting in rapid crack propagation.(4)The changes of the number and scale of microcracks in rock at different loading stages can be effectively reflected in the AE b value and AE ΔF value,which are highly coupled with the rock damage degree and can be used to quantitatively evaluate the rock damage state.The research results can provide some guidance and reference for the stability and damage assessment of engineering rock mass.
rock mechanicsstress disturbancemechanical characteristicscrack developmentAE damage index
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