Experimental Study On Crack Propagation Of Rock Blasting Under Initial Stress State

The coal-dominated energy system has supported the rapid development of China's national economy.At present and for a long time to come,coal will still be our country's leading energy source.With the transformation of modern mines from shallow to deep,the in-situ stress in rock mass is increasing,which causes the theory of rock blasting and fragmentation in deep mines and the stability mechanism of surrounding rocks to be significantly different.Therefore,it is very important for theoretical research and engineering application to correctly understand the loading characteristics of explosive load,damage evolution mechanism of rock mass blasting,influencing factors of blasting effect and rock breaking mechanism of different blasting techniques under high in-situ stress.Based on the guidance of these theories,‘explosion mechanics','continuum mechanics',‘rock fracture and damage mechanics','stress wave theory',etc.,this paper conducts a comprehensive study on rock blasting fracture mechanism under the initial state of high in-situ stress through the research methods of physical similarity model test and theoretical analysis,where theoretical analysis is a supplement to physical similarity model test.This includes:1)modifying calculation formula for radius of crushing and crack circle with consideration of the initial stress 2)modifying blasting fractal damage model with consideration of initial stress 3)revealing the quantitative relationship between initial in-situ stress and direction,length and velocity of blasting crack propagation in deep rock mass 4)revealing the relationship between initial in-situ stress and propagation of blasting stress wave 5)exploring effect of uncoupling coefficient on blasting crack propagation under initial stress condition.The model test of transparent rock blasting under the initial stress state shows that the average length and velocity of main crack propagation of model specimens decreases with the increase of initial in-situ stress,and the average diameters of annular fracture circle and compression crushing circle also decreases with initial stress increases,but the ratio of diameter of compression crushing ring to diameter of annular crack ring increases with the increase of initial stress.At the same time,stress wave in blasting far zone in the area with the larger initial stress is stronger than the area with the smaller initial stress,that is,the vibration intensity becomes larger.When model specimens under unequal confining pressure load conditions,the Angle between the direction of the longest radial main crack propagation during explosion and the direction of maximum principal stress(?v)is acute Angle,and the magnitude of this acute Angle increases with the increase of the minimum principal stress.At the same time,the value of ? can be calculated by tan?=?v/?h(0<?<45?),which is highly consistent with the theoretical analysis.From the above conclusions,it can be inferred the initial in-situ stress affected the distribution of energy of the explosive after the explosion,that is,the ratio for energy dissipated in near and far blasting zones increases,and ratio for the energy dissipated in blasting middle zones decreases.That is why the deep rock mass is difficult to explode under high in-situ stress.The initial stress limits the opening of the crack surface,leading to require a large driving force for crack propagation and a large amount of energy for crack propagation per unit length.However,the total energy used to drive crack propagation is reduced(blasting middle zones),so the total length of crack propagation is reduced.Figure 96 table 52 reference 240...