Study On Impact Dynamic Characteristics And Crack Propagation Of Fractured Rock Mass

There are many initial damages in the natural rock mass,such as joints,cracks and faults.And rock mass with fracture in practical engineering often disturbed by dynamic load like rock blasting,earthquake and underground space excavation.The existence of these nonlinear structural surfaces in rock mass will have a serious effect on the dynamic mechanical properties of rock mass.Studying the dynamic mechanical properties of fractured rock mass is of great significance for fully understanding the mechanism of crack propagation,the strength and deformation characteristics of fractured rock mass and the stability control of underground space.In order to analyze the crack fractal characteristics and the dynamic mechanical properties of fractured rock mass under impact load.The dynamic compression experiments under different joint characteristics and different loading rates have been carried out,adopting the method of theoretical analysis and impact test.The main contents and results are as follows:(1)Based on the drop hammer impact test system,the impact tests of rock specimen with different joint dip angles,different joint numbers,different drop weights and different drop hammer heights have been carried out.The dynamic stress-strain relationship,dynamic mechanical parameters and energy absorption law are analyzed.The following conclusions are obtained: the stress-strain of different joint angles and different joint numbers have experienced fore stages,namely,elastic deformation stage,stable stage of fissure development,unstable stage of fissuredevelopment and post failure stage.The peak strain and maximum vertical deformation have a positive correlation with the falling height,weight of the hammer and the number of prefabricated fractures.The peak strain of 60°,30°,45°,90°and 0 ° angles increases in turn.The maximum vertical deformation of the 0 °,45 °,60 °,30 ° and 90 ° angles is increasing in turn.The dynamic compressive strength and dynamic elastic modulus of the fractured rock have a negative correlation with the number and the angle of prefabricated fractures.The impact process of the test satisfies the momentum impulse conservation relation.According to the principle of conservation of energy,under the same quality and different height impact test conditions,the energy absorbed by fractured sandstone is only a small part(about 26.7%)of the gravity potential energy of heavy hammer.The rest of the energy is consumed by heavy hammer,aluminum gasket and force sensor.However,the same energy is used in the same way.Under the same height and different quality impact test conditions,the energy absorption is just the opposite.(2)Based on the fractal theory,the fractal characteristics of the crack propagation and evolution of the sandstone during the impact process are described quantitatively.And a fractal growth model for dynamic crack propagation process is established.In addition,the fractal dimension of crack is related not only to the crack density and crack width,but also to the crack propagation rate and loading rate.