Strain rate effect and energy dissipation characteristics of sandstone in coal measures under impact loading

The deformation of surrounding rock will increase under dynamic load during the excavation of coal mine roadway.In order to study the mechanical properties and energy dissipation of sandstone in coal measures under impact loading,the sandstone in the surrounding rock of Chensilou coal mine roadway was collected as the research sample,and a split Hopkinson pressure bar test device,with a diameter of 50 mm,was used in uniaxial single impact compression test and cyclic impact compression test.The strain rate effect,energy dissipation characteristics and failure modes of the sandstone were analyzed.Under the uniaxial single impact loading,with the increase of average strain rate,peak stress and peak strain,the plasticity and strength of the sandstone samples increase,while the secant modulus decreases gradually.Moreover,the peak strain has a linear increase relationship with the average strain rate,and the peak stress approximately increases with the 1/3 power of the average strain rate.With the increase of the average strain rate,the absorption energy per unit volume of the sandstone samples shows a linear increase tendency,and the degree of fragmentation of the samples continues to increase.Under the impact of constant compressive stress,the internal cracks of the sandstone samples keep crossing and expanding,and the splitting failure occurs along the axial direction.Under the cyclic impact loading,the average strain rate and peak strain of sandstone samples gradually develop with the increase of the cyclic loading times,while the peak stress,secant modulus and second type secant modulus gradually decreases.During the cyclic impact under the fixed pressure,with the increase of the impact times,the incident energy basically remains unchanged,and the reflection energy and absorption energy gradually increase,whereas the transmission energy gradually decreases.The absorption energy per unit volume of the sandstone samples increases slowly firstly and then suddenly in-creases with the impact times.Under the cyclic impact loading,the energy absorption capacity of the sandstone samples is enhanced.With the increase of impact times,the distribution of microcracks inside the samples enlarges and the expansion speed accelerates.As a result,the tensile failure mainly occurs,and the annular failure plane running through the sandstone samples generates along the axial loading direction.