Numerical Study On The Characteristics Of Explosion Stress Wave And The Breaking Effect Under Different Blasting Conditions

The mechanism of rock blasting has always been a key issue in the study of rock blasting theory and engineering technology.At present,the blasting community has basically reached a consensus that rock fragmentation or rupture is the result of the combined action of explosive stress waves and blasting gas.However,whether the two contribute the same to rock fragmentation and fracture has not been clear so far.In fact,for different blasting methods,blasting parameters and charging conditions,the effects of the two are likely to be different.Study and clarify the respective effects of explosion stress wave and blasting gas on breaking and rupture in different blasting methods,which will help to select blasting parameters reasonably and improve the blasting effect,especially when studying rock blasting damage and fracture characteristics.The different functions of the two are the prerequisites for achieving effective control of blasting damage and rupture.Based on the theory of rock blasting,this paper uses a nonlinear finite element method to study the rock fragmentation and rupture mechanism of the columnar charge under different blasting methods from the perspective of blast stress wave breaking.According to different ground stress levels,free surface conditions,minimum resistance line and hole spacing,the rock mass blasting calculation models under different blasting conditions are established to study the characteristics of rock mass fragmentation and rupture and its changing laws under the action of explosive stress waves.Taking the blasting test of a cylindrical rock specimen as the research object,an ANSYS/LS-DYNA numerical calculation model for rock specimen blasting is established,and the corresponding HJC constitutive model parameters are determined by combining theoretical formulas and empirical value methods.The range of the crushing circle in the near area of the blast hole and the expansion pattern of the radial burst pattern in the far area obtained by the simulation calculation are very consistent with the results of the indoor model test,which shows that the calibrated material parameters are used to analyze and study the characteristics of the explosion stress wave on rock blasting It is feasible and reliable.The Dynain file method is used to simulate the loading conditions of hydrostatic in-situ stress,uniaxial in-situ stress and unequal two-way in-situ stress.Based on this,a numerical model of rock blasting under different in-situ stress conditions is established,and the propagation characteristics of the explosion stress wave are studied.And the law of burst pattern expansion.The research results show that the propagation of radial cracks will be restrained to the same extent under hydrostatic ground stress,and will show obvious directionality under unequal ground stress,and the cracks will expand significantly in the direction of larger initial ground stress.Based on ANSYS/LS-DYNA numerical software,the vibration characteristics,stress distribution characteristics and fracture characteristics of rock masses under different reflection boundary conditions are studied.The analysis results show that the reflected wave will cause secondary disturbance of the surrounding rock,resulting in the increase of peak vibration velocity and peak tensile stress near the free surface,which may cause reflection tensile spalling,and the location of spalling starts at a certain point near the free surface.Numerical simulation methods are used to study the characteristics of rock vibration and failure when the minimum resistance line changes,and the characteristics of the joint formation of two adjacent blastholes in the direction of the centerline when the blasthole spacing changes.The results show that the stress wave reflection tensile spallation only occurs when the resistance line is very small;two adjacent blast holes detonate at the same time,and the effective stress in the direction of the blast hole connecting center line shows a trend of first decreasing and then increasing from the hole wall to the midpoint of the connecting center line.,The cracks between the holes started from the hole wall and gradually developed towards the blast hole connecting center line,which confirmed the defects of the traditional stress wave cracking mechanism.