Effect Of Dynamic Load And Geo-stress On Response Characteristics Of Rock

In the process of underground rock mass engineering blasting excavation,the ground stress of rocks at different spatial locations is different,and due to the stress wave attenuation effect,the size of the rocks at different distances from the blast source is different,and the rocks have different dynamic response characteristics under different ground stresses and dynamic loads,and it is of great significance to study the dynamic response characteristics of rocks for controlling the blasting effect.In order to study the influence of ground stress and dynamic load on the dynamic response characteristics of rocks,the improved SHPB test device is used to set up 5 axial static loads and 5 impact velocity levels,which are combined to simulate ground stresses and dynamic loads of different sizes,and apply different sizes of dynamic loads to red sandstones with different three-dimensional static loads for impact testing.The variations of characteristic stress,characteristic strain,fragmentation block degree and energy transfer of red sandstone under different three-dimensional static load and impact velocity are analyzed,and an empirical model of rock dynamic response parameters changing with impact velocity or static load is constructed,and the evolution mechanism of rock dynamic response characteristics is analyzed.The main contents and achievements are as follows.(1)In the three-dimensional impact test,when the three-dimensional static load is unchanged,the stress wave amplitude increases with the increase of the impact velocity;when the impact velocity is unchanged,with the increase of the axial static load,the transmitted wave amplitude increases first and then decreases,while the reflected amplitude decreases first and then increases.(2)When the three-dimensional static load is fixed,with the increase of the impact velocity,the average strain rate and the ultimate strain of the red sandstone increase as a power function.The impact rate on the dynamic deformation modulus of the rock is not obvious;under the same impact velocity,with the increase of the axial static load,the ultimate strain of the red sandstone decreases first and then increases,the first dynamic deformation modulus of the red sandstone shows an overall increase trend,and the second dynamic deformation modulus of the red sandstone increases first and then decreases.(3)When the three-dimensional static load is fixed,the peak stress of the red sandstone increases with the increase of the impact velocity in a power function,which is mainly due to the increase of the rock damage with the increase of the dynamic load;when the impact speed is fixed,the peak stress of the rock increases first with the increase of the axial static load and then decreases,and the axial static load corresponding to the turning point decreases slightly with the increase of the impact rate,which is mainly due to the fact that the peak stress of the rock is affected by the static load and the dynamic load.With the increase of axial static load,the critical impact velocity of red sandstone and the dynamic compressive strength of the three axes increase first and then decrease.(4)The experimental results show that with the increase of impact velocity,the failure evolution of red sandstone specimens with three-dimensional static load shows three failure stages of "overall integrity-through-through crack-cone failure";red sandstone specimens with three-dimensional static load have a variety of failure modes,and tensile failure occurs first under the action of dynamic load,such as the dynamic load after tensile failure occurs in red sandstone,and then shear-crushing failure occurs,and the tapered body is still retained after rock destruction.The failure mode of red sandstone with three-dimensional static load under dynamic load is not significantly related to the size of the axial static load of red sandstone,but the axial static load has a significant impact on the degree of fragmentation of red sandstone.(5)The distribution of red sandstone fragmentation blocks is sensitive to changes in impact velocity and axial static load.Under the same three-dimensional static load,the greater the impact velocity,the smaller the average crushing particle size of the red sandstone,the greater the degree of failure of the red sandstone,and the greater the proportion of small and medium particle size in the crushing particle size.At the same impact velocity,the average crushing particle size of the red sandstone gradually decreases as the axial static load increases.In the three-dimensional dynamic impact test,the law of fracture fractal dimension of rock is not obvious.(6)When the three-dimensional static load is the same,with the increase of the impact velocity,the incident energy shows a bi-term increase trend,and the absorption energy and the impact velocity show a logarithmic function relationship;at the same time as the impact velocity,with the increase of the axial static load,the absorption energy decreases,and the energy absorption of the rock is related to the initial damage caused by the static load.Under the same static load conditions,the greater the absorption energy of the rock,the higher the degree of damage to the rock.