Experimental Study On Impact Mechanical Properties Of Red Sandstone Under Three-dimensional Static Stress

In order to study the dynamic characteristics of rocks and the dynamic mechanism of rockburst,the red sandstone was used as the object of study in this experiment.To analyze the deformation characteristics,strength characteristics,energy dissipation,failure modes of red sandstone and other dynamic characteristics,a impact loading test was carried out.The red sandstone was preloaded under the three-dimensional high static stress by using the modified Hopkinson pressure bar.At the same time,the dynamic mechanism of the rockburst was analyzed based on the dynamic characteristics of the red.sandstone under the three-dimensional static-dynamic coupling load.The research indicates that:1.The stress-strain curve of the red sandstone is divided into four stages under uniaxial compression conditions,namely compaction stage,elastic stage,development stage of the destruction and stage of failure respectively.There are three types of failure modes under uniaxial compression conditions,namely tensile failure,single slope shear failure and X-shaped conjugate slope shear failure.2.Compared with the uniaxial compression,the stress-strain curve of the red sandstone under the three-dimensional dynamic and static loading has only three stages,namely,the elastic stage,development stage of the destruction and the failure stage,there is no compacting stage anymore.There are three types of stress-strain curves for the red sandstone at different strain rates,strain resilience,stress drop and post-peak plasticity.When the axial pressure is constant,the secant modulus increases as the confining pressure increases.When the confining pressure is constant,the secant modulus increases first and then decreases with the increase of the axial pressure.When the axial pressure is constant,the average strain rate decreases with the increase of the confining pressure.When the confining pressure is constant,the average strain rate decreases first and then increases with the increase of the axial pressure.3.The dynamic compressive strength of red sandstone increases with the increase of confining pressure when the axial pressure is constant.When the confining pressure is constant,the dynamic compressive strength of red sandstone increases first and then decreases with the increase of axial pressure.The dynamic compressive strength of red sandstone increases with the increase of strain rate,and it shows a good strain rate correlation under the three-dimensional static-dynamic coupling load.Under the three-dimensional static-dynamic coupling load,the dynamic compressive strength growth factor of red sandstone increases linearly with one third of the strain rate,and they have good linear correlation fitting.4.Under the three-dimensional static-dynamic coupling load,when the axial pressure is constant,the absorption energy per unit volume increase first and then decrease with the increase of confining pressure.When the confining pressure is constant,the absorption energy per unit volume increases first and then decreases with the increase of axial pressure.The absorption energy per unit volume,the incident energy and the average strain rate show a incremental linear relationship,and they have good linear correlation fitting.5.For the red sandstone under the three-dimensional static-dynamic coupling load,the degree of damage increases with the increase of the strain rate.When the axial pressure is constant,the degree of damage decreases with the increase of the confining pressure.When the confining pressure is constant,the degree of damage increases with the increase of the axial pressure.When there is no confining pressure,the rock shows the shear failure mode of either an "X" or a "double cone";under the three-dimensional static-dynamic coupling load,the rock shows the shear failure mode of a cone or a conical frustum.6.According to the results of the red sandstone's dynamic response obtained from the experiment and the regularity under the condition of three-dimensional static-dynamic coupling load,we can conclude that a rock which stores large amounts of elastic strain energy and is in the peak intensity state is unstable.Furthermore,disturbing the rock by external factors under this condition would cause loss of stability.