Experimental Study On The Dynamic Properties And Energy Consumption Characteristics Of Granite Under Cyclic Impact Loading

In practical applications,the drill and blast method is one of the most commonly used methods for rock tunnel excavation in the world.In the process of drilling and blasting construction,the surrounding rock is often subjected to cyclic dynamic loads,which affects the dynamic characteristics of the rock,and then affects the stress and stability of the tunnel.However,at present,the research on the mechanical properties and damage evolution of rocks under cyclic shock loading is still insufficient.Therefore,it is of great significance to study the dynamic properties of rocks under cyclic explosion loads,especially the energy dissipation and damage evolution.This paper takes granite as the research object,cyclic impact tests under different impact loads on granite specimens with a diameter of 100 mm by the SHPB test system with a diameter of 100 mm.The dynamic performance,energy dissipation,damage evolution and failure form of granite are discussed and analyzed in detail.The main research contents and conclusions are as follows:(1)The granite uniaxial cyclic impact test was carried out based on the SHPB test device with a diameter of 100 mm,Four impact speeds of 7m/s,8m/s,9m/s and 10m/s are used as different cyclic impact loads,The dynamic mechanical properties,energy dissipation laws,damage accumulation effects and failure modes of granite are discussed and analyzed.The results show that,With the increase of the number of shocks,the peak stress of the granite sample decreases linearly,the peak strain increases linearly,and the dynamic elastic modulus shows a decreasing trend as a whole.The energy evolution of granite under different impact velocity can be approximately divided into three stages: linear elastic deformation phase,plastic deformation phase,specimen failure stage.The damage of the specimen accumulates continuously with the increase of the number of impacts,and the greater the impact speed,the faster the damage variable growth rate.The failure modes of the granite specimens show two failure modes: shear failure under low-speed impact and split failure under high-speed impact.(2)Cyclic impact test was carried out on granite specimens with a diameter of 100 mm and an slenderness ratio of 1,0.75,0.50,and 0.25,respectively to investigate the size effect of granite under cyclic impact loading.At the same impact speed,the smaller the slenderness ratio of the sample,the less the number of impacts required for its failure,and the damage will increase faster.The peak strain of the specimen decreases with increasing slenderness ratio,while the peak stress is almost independent of the slenderness ratio.At the same impact speed,the larger the slenderness ratio of the sample,the greater the degree of fragmentation,which is manifested as a decrease in the degree of fragmentation and an increase in the number of fragments.(3)The cyclic impact test of granite under three confining pressure states of 2MPa,4MPa and 6MPa was carried out on the SHPB test device with confining pressure.The study found that with the increase of confining pressure,the average strain rate of the sample gradually increased,and the peak deviatoric stress increased to some extent.The dynamic enhancement factor of the sample is the largest at 6MPa confining pressure,and decreases slowly with the number of shocks.Under the confining pressure of 2MPa and 4MPa,the crack width on the surface of the granite sample is larger,and when the confining pressure is 6MPa,the fine cracks are mainly distributed uniformly.