Study On Dynamic Strength And Deformation Characteristics Of Red Sandstone Induced By Ground Stress And Water Pressure

The deep rock mass is in a high geo-stress and high water pressure geological environment,the dynamic mechanical properties of rocks are deeply affected by the occurrence environment.Under the action of dynamic disturbance loads such as blasting excavation,the geo-stress and water pressure of the surrounding rock mass on the excavation unloading surface change with the change of excavation depth,which leads to different dynamic mechanical response characteristics of the rock.It is of great significance to study the dynamic response characteristics of the rock under high geo-stress and high water pressure for the safe construction effect.In order to study the influence of high geo-stress and high water pressure on the dynamic response characteristics of rock,based on the self-developed high water pressure and high geo-stress rock dynamics test device,six kinds of water pressure and four kinds of axial static stress levels were set up.The red sandstone under different water pressure and geo-stress was subjected to the same dynamic load to simulate the mechanical environment of deep rock mass engineering excavation and the mechanical environment of excavation strong disturbance under the action of high water pressure and high geo-stress.The variation law of characteristic stress and characteristic strain of red sandstone and the strain rate correlation between characteristic stress and characteristic strain of rock under different water pressure and geo-stress are analyzed.The empirical model of rock dynamic response parameters with water pressure and average strain rate is constructed,and the evolution mechanism of rock dynamic response characteristics is analyzed.The main contents and results are as follows:(1)The rock stress-strain curve obtained from the impact test is roughly divided into four sections,the elastic stage,the loading stage,the first unloading stage,and the second unloading stage.The existence of water-free pressure,the stress-strain curve of rock shows the characteristics of type I stress-strain curve.The existence of water pressure,rock deformation is affected by water pressure,and its stress-strain curve shows the characteristics of type II stress-strain curve.(2)The axial static stress is constant,the peak stress,critical unloading stress and residual stress of rock increase with the increase of water pressure.The peak stress show a good logarithmic function distribution with water pressure,and the residual stress and critical unloading stress of rock both obey a good exponential function distribution with the increase in water pressure.With the increase of water pressure,the growth trend of rock characteristic stress gradually slowed down,and the slope of the fitting curve gradually decreased.The ultimate strain,residual strain and average strain rate of rock decrease with the increase of water pressure.The ultimate strain,residual strain and average strain rate of rock obey exponential function distribution with water pressure.When the water pressure increases to a certain value,the rock strain rate,strain and other parameters tend to be stable.The elastic modulus of rock increases with the increase of water pressure.When the water pressure increases to a certain value,the effect of axial static stress on the deformation modulus of rock is weakened.(3)The stress and deformation parameters of rock have strong strain rate correlation.The axial static stress is constant,the peak stress,critical unloading stress,residual stress and elastic modulus of rock decrease with the increase of average strain rate,and the ultimate strain and residual strain of rock increase with the increase of average strain rate.The peak stress,critical unloading stress,residual stress,and deformation modulus and average strain rate have a good negative linear relationship;and the ultimate strain,the residual strain and the average strain rate of the rock have a good postive linear relationship.(4)As a porous fractured rock mass,the mechanical properties of sandstone change under the action of water pressure and axial static stress.The water pressure is small,and the existence of axial static stress makes some pores of the rock closed.The water in the closed pores contributes part of the stiffness to resist external loads.As the axial static stress increases to a certain value,the existence of pressure water leads to the decrease of rock strength.The water pressure is large,and the existence of pressure water causes the internal structure of the rock to change,and the bound water effect is continuously enhanced.At the same time,under the action of impact load,the compressive deformation of rock leads to the development of cracks.The Meniscus effect,Stefan effect and Newton internal friction effect of free water in cracks inhibit the initiation and propagation of cracks,thereby improving the strength and deformation resistance of rock.