Basic Experimental Study Of Roof Unloading Rebound And Dynamic Failure Mechanism Of Strong-Weak Surrounding Rock Combination Structures

Coal in plastic zone of roadway side and coal in deep main bearing area support roof as composite structure.Coal in main bearing area bears main load.When the coal body in main bearing area is damaged,the compression deformation of roof in elastic stage will inevitably recover,which will form a "rebound" effect on coal body.In this paper,the plastic zone coal body and the main bearing zone coal body are taken as composite structure,and the roof is taken as loading body.The failure of the main bearing body and the unloading rebound characteristics of the roof and the action mechanism of the composite structure are studied.The main conclusions of this study are as follows:(1)Laboratory tests of uniaxial compression of coal and rock mass were carried out by using a low stiffness material testing machine.The acceleration of the press head of the testing machine was monitored by an acceleration sensor during the loading process.The test results show that when the failure bearing capacity of coal decreases,the pressure head of the test machine produces acceleration and the acceleration is positively correlated with the load reduction.The influence of the stiffness of the testing machine on the unloading rebound characteristics is analyzed by numerical simulation.The results show that the unloading rebound speed has a linear relationship with the stiffness of the testing machine within the range of the stiffness of the testing machine and the stiffness of the specimen.(2)Laboratory tests of uniaxial compression of strong and weak composite structures were carried out,and the surface strain of weak specimens was measured synchronously.The test results show that when the strong and weak specimens are connected in parallel,the weak specimens themselves will not suffer from dynamic damage.When the strong specimens are damaged,the test machine will rebound and the weak specimens will suffer from dynamic damage.By analyzing the change of the strain value at several locations on the surface of the specimen in the composite structure during the rebound process of the testing machine,the strain rate of the coal body reaches 70s-1 under the rebound action of the testing machine,and the impact of the rebound of the testing machine on the weak specimen belongs to the dynamic load.(3)The numerical tests of uniaxial dynamic load impact of coal and rock mass with different stress levels were carried out.The results show that the increment of energy is basically the same when the specimens in the peak and post-peak stages are impacted by dynamic load,while the specimens in the post-peak stage consume less energy and convert more kinetic energy.Therefore,the specimens in the post-peak stage are more prone to dynamic damage when they are subjected to dynamic load.