Experimental Study On Dynamic Mechanical Properties Of Rock Under Combined Dynamic And Static Loading

The demand for energy has been increasing with the rapid development of economy,the huge consumption of mineral resources makes the shallow resources of our country gradually exhausted,and the mineral resources such as coal have developed to the deep.With the increasing of coal mining depth,the stress state of deep roadway rock is more complicated,which often is disturbed by blasting vibration,excavation and unloading.Therefore,in order to have a more systematic and comprehensive understanding of the mechanical properties of common rocks in coal mines under the impact load,taking the surrounding rock of Chensilou coal mine as the research background,an improved Split Hopkinson Pressure Bar(SHPB)was used to test the dynamic mechanical properties of sandstone,carbonaceous mudstone and sandy mudstone under impact loading.The research contents and conclusions are as follows:(1)The coal mine roadway surrounding rock was samples on site,the physical and mechanical properties of the surrounding rock were tested from the aspects of density,ultrasonic wave velocity,uniaxial compression and Brazil splitting in the laboratory,and the basic physical and mechanical parameters of the rock were obtained;(2)The SHPB conventional uniaxial impact compression test,cyclic impact compression test and dynamic splitting test were carried out on the rock samples by using the SHPB test device.The results showed that: under the impact load,with the increased of the strain rate,the dynamic compressive strength of the rock samples increased,and the peak strain increased,showing an obvious strain rate effect.Under cyclic impact load,with the increased of impact times,the peak strain of the samples gradually increased,and the peak stress gradually decreased.The absorption energy per unit volume first increased slowly and then increased suddenly,and the samples is mainly subjected to axial splitting tensile failure;(3)The dynamic compressive strength and peak strain of the samples were further increased during the one-dimensional static and static SHPB impact test.The stress-strain curve of the rock samples could be divided into elastic stage,plastic stage and failure stage,and the plastic deformation stage was more obvious.With the increased of the impact pressure,the samples transitioned from a more complete state to a state of crushing and crushing,and formed a fracture surface along the axial and annular directions,causing axial splitting tensile failure and compression shear failure;(4)In the impact test of three-dimensional combination of static and static SHPB,with the increased of incident energy or peak strain,the reflected energy,transmitted energy,absorbed energy and absorbed energy per unit volume all showed a linear increased trend.As the strain rate increased,the absorbed energy per unit volume gradually increased.Axial compression limited the transverse deformation of the samples,while confining pressure limited the circumferential deformation of the samples.Under the combined action of axial compression and confining pressure,the dynamic compressive strength of the samples was significantly improved.