Development Of The Impact Test System With Energy Storage Of Drop Hammer And Experimental Study Of Coal Rocks Under Dynamic And Static Combination Loading

With the deepening of the mining depth,the stress state of the surrounding rock is more complex,the resulting rock burst has increased dramatically.The coal rock under the mine is already under static load,such as stress and tectonic stress,meanwhile,it is also affected by the dynamic disturbances including the rupture of hard roof plate and artificial blasting.When the stress wave spreads to a place with a strong impact,it is possible to induce the disaster of rock burst.On the basis of previous work,an impact test system with energy storage of drop hammer is designed and developed.The system consists of frame,static load loading system,impact load loading system,load control system and high speed data signal acquisition system.The system can add axial impact load,axial static load and lateral static load to the sample individually and implement loads coupled different dynamic and static loads.The system use large size samples and the impact load added to the samples is more close to actual.The high precision sensors such as impact sensors and dynamic strain gauge for real-time monitoring are used to record the samples' strain and impact load.The experiment was carried out by using the system for different combinations of static load and impact load of the samples of coal and concrete.The results show:the ability of coal sample to withstand dynamic shock is greater than that of static load,and the ability is firstly increase and then decrease with the increase of axial load.When the shock load is large,the crack of coal is less and the debris is larger.When the axial load is large,the crack in the coal sample is more,and the debris is smaller.Coal sample strain rate measured in experiment ranges in the 1-10,which is closer to the actual strain rate range.The result show that the system can more truly simulate the stress state of coal and rock mine.The strength of the concrete sample increases firstly and then decrease with the increase of the axial load,and when the axial load is the 80%of the static load strength reaches the maximum.The modulus of the concrete sample increases firstly and then decrease and when the axial load is the 80%of the static load strength reaches the maximum.The pressure shear fracture is produced under the load of the combination of static load and impact load,and the shear failure of the double cone is finally presented.