Study On Dynamic Energy Dissipation And Failure Mechanism Of Red Sandstone With High Ground Stress And High Water Pressure

With the gradual increase of underground engineering depth,the underground environment of deep engineering rock mass also changes.The existing underground engineering rock mass is mostly in the water pressure and ground stress environment.Water pressure and ground stress will change the physical and mechanical properties of rock,and show different response characteristics under the action of blasting,and even cause major engineering disasters such as water inrush,restricting the safety and stability of underground rock engineering.In order to realize the safe and efficient excavation of rock mass engineering under water pressure and ground stress,this paper studies the dynamic energy dissipation and failure characteristics of rock under water pressure and axial static stress.The main research contents and conclusions are as follows:(1)In order to study the influence of water pressure and ground stress on the energy dissipation and failure characteristics of rocks,the dynamic test system of rocks with high water pressure and high ground stress developed by ourselves is used to set multiple groups of water pressure and axial static stress levels to simulate the environment of water pressure and ground stress,and carry out impact tests on rocks.The dissipated energy of rock is calculated based on the incident wave,reflected wave and transmitted wave,and the relationship between the energy dissipation rate of rock and the water pressure and the axial static stress is studied.The rock specimen after impact is screened and its mass fractal dimension is calculated,which is used to characterize the damage degree of the rock specimen and study the influence law of water pressure and axial static stress on the fractal dimension of rock.In order to analyze the influence of water pressure and axial static stress on rock microcrack growth,the pore crack growth model was improved to explore the influence mechanism of water pressure and axial static stress on rock failure characteristics.(2)When the axial static stress is constant,with the increase of water pressure,the energy reflectance of the rock presents a trend of rapid decline first and then slow decline,and the rate of change gradually decreases,and the energy transmittance of the rock gradually increases.The energy reflectance and energy transmittance of the rock show a power function relationship with the water pressure.The energy dissipation rate of rock increases first and then decreases with the increase of water pressure.The smaller water pressure can promote the utilization rate of incident energy of rock.When the water pressure is constant,the energy dissipation rate of rock increases linearly with the increase of axial static stress,and its increasing rate decreases with the increase of water pressure.(3)With the increase of water pressure,the failure mode of rock specimens under axial static stress presents a change trend of "crushing failure-cone failure-conjugate failure-unbroken",but the relationship between the change of failure mode and axial static stress under water pressure and axial static stress is not obvious.Water pressure and axial static stress have obvious effects on the fragmentation distribution of rock fragments.With the increase of water pressure,the mass proportion of small and medium particle size fragments to medium particle size fragments gradually decreases,but with the increase of axial static stress,the opposite trend is presented,the mass proportion of small and medium particle size fragments gradually increases,while the mass proportion of large particle size fragments gradually decreases.The fractal dimension of mass applied to rock is calculated to quantify the damage degree of rock specimen.The results show that the fractal dimension gradually decreases to 0 with the increase of water pressure,while the fractal dimension of rock gradually increases with the increase of axial static stress.(4)In order to better analyze the influence mechanism of water pressure and ground stress on rock failure characteristics,the pore-emanated crack model was modified under water pressure and axial static stress,and the dynamic stress intensity factor and dynamic fracture toughness of rock under water pressure and axial static stress were obtained.With the increase of water pressure,the dynamic stress intensity factor of rock gradually decreases,the minimum initiation radius increases,and the number of cracks that can occur in rock decreases.Water pressure inhibits the initiation and propagation of micro-pores in rock,and finally the macroscopic failure of rock is gradually weakened.With the increase of axial static stress,the dynamic stress intensity factor of rock increases continuously,the minimum initiation radius of rock increases,and the axial static stress will promote the propagation of rock microcracks and improve the damage degree of rock.The variation trend of rock failure degree with water pressure and axial static stress obtained by pore crack growth model is consistent with the experimental results.