Study On Rock Fragmentation Mechanism And Parameter Optimization Of Shaped Charge Blasting In Tunnel Engineering

In recent years,as the scale and difficulty of tunnel projects construction have increased,most of the rock tunnels are still constructed by the mining method.However,the traditional mining method often has the problems of over-or-under excavation,which cannot guarantee the tunnel stability.Tunnel shaped charge blasting has the advantages of reducing surrounding rock disturbance,preventing over-or-under excavation.It is an energy saving and environmental protection blasting technology with broad application prospects.Studying the accumulation fragmentation mechanism has practical significance for guiding engineering applications.Numerical simulation,theoretical analysis,plexiglass test and field application are used to reveal the mechanism of oriented fracture controlled blasting and optimize the shaped charge parameters.The main research contents and conclusions are as follows:（1）This paper firstly uses SPH numerical methods to compare with existing experiments to demonstrate the method effectiveness.Then the blasting mechanism and the influence of the shell and the charge type cover are analyzed.Finally,the cone angle parameters of copper and PVC is optimizing,and the influence of different shell shapes is analyzed.The results show that as the shell thickness increases,the detonation becomes more stable and the jet velocity increases;As the cover thickness decreases,the explosive gas reduces the work done on the cover,and the more the flow energy is converted into a shaped energy jet,the greater the jet velocity,but no obvious energy accumulation effect is formed when the thickness is 0;As the cone angle decreases,the charge area decreases and the jet velocity increases,but the quality used to form the jet decreases;Different shell shapes have different effects on the jet flow.The jet head velocity formed by the elliptical + linear shell is basically the same as that formed by the elliptical shell,but the former saves the amount of charge compared with the latter.In addition,the velocity formed by the two shells is smaller than that of the linear shell.（2）The rock fragmentation mechanism by shaped charge blasting is analyzed by theoretical,experimental and numerical methods.The results show that the initial shock wave load value in the energy gathering direction is significantly greater than that in the non-energy gathering direction,and the peak load action time is earlier than the non-energy gathering direction;Since the crushing zone consumes a large amount of shock explosion energy,the shock wave decay rate in the near zone is faster,in the middle and far zone is slow,and the difference in explosive load in the middle and far zone is small;The superimposition effect of the reflected wave makes the non-energy-concentrating direction appear the second stress peak lagging behind the initial shock wave,but the value is relatively small.（3）Taking the radial and axial non-coupling coefficients and the explosive position as the test factors,the crack propagation length and width in the energy gathering direction,the ratio of the crack propagation length and the ratio of the crack propagation width are used as the evaluation index.A three-factor four-level orthogonal test is established,and the optimal parameters combination is obtained: the diameter of the blast hole is 90 mm,the axial decoupling coefficient is 1.25,and the explosive position starts at the bottom.Then studing the blasting effect of different blast hole spacing and optical blasting layer thickness,so as to determine the optimal parameter combination: the blast hole spacing is 700 mm,the light blasting layer thickness is 600 mm.The optimization results are applied to the Jinjing Tunnel blasting construction site of Xingquan Railway.