The Influence of Peripheral Holes External Insertion Angle on the Smooth Blasting Effect of Tunnels
With the relationship between hole spacing and external insertion angle established,the simulations of tunnel blasting process were analyzed under the conditions of the external insertion angle at 3° and randomly selected among 3°,4°,and 5° respectively.The results indicate that changes of external insertion angle will change the spatial position relationship between peripheral holes and affect the distribution pattern of blasting stress waves.In both cases,the attenuation speed of stress waves in peripheral hole blasting decreases from fast to slow with increasing distance.When the external insertion angle is inconsistent,the blasting stress wave in the peripheral holes protecting surrounding rock mass is superimposed and enhanced in multiple parts,and is unevenly distributed along the tunnel excavation contour,resulting in overbreak in more parts,which is not conducive to the formation of a smooth and flat tunnel excavation profile.Therefore,in engineering practice,it is necessary to strictly control the external insertion angle.
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