Study On Application Of Smooth Blasting Technology In Full-Section Excavation Of Subway Tunnel

The drilling and blasting method is widely used in various tunnel construction operations as a fast and economical method of excavation.However,the strong blasting load during the blasting inevitably damages the surrounding rock of the tunnel.How to control the degree of damage caused by blasting to the surrounding rock during the construction process,so that the stability of the surrounding rock after the tunnel excavation meets the engineering requirements is a key issue to improve the construction quality of the tunnel.The damage of surrounding rock is one of the important factors that affect the stability of the tunnel.Research on the damage of surrounding rock after blasting can provide a reliable basis for the design of blasting scheme.A reasonable blasting scheme can not only control the damage caused by blasting loads to the surrounding rock,but also greatly improve the construction safety,economy and efficiency.The paper is based on the engineering background of the tunnel between the KeXueGuangChang station and SuYuan station of Guangzhou Metro Line 21.Field tests,theoretical analysis and numerical simulation were all used to analyze the damage range of rock under blasting load.Several blasting tests and sonic wave testing were conducted on the site under both the conventional blasting scheme and the smooth blasting scheme.The test results show that after the blasting of the smooth blasting scheme,the wall surface of the tunnel is flat and there is no obvious phenomenon of overbreak and underbreak.The blasting effect is better than the conventional blasting scheme.After the smooth blasting,the left tunnel has a lesion dimensions of 39.0cm and the right tunnel has a lesion dimensions of 45.5cm,which is smaller than the conventional blasting scheme.The damage degree of the surrounding rock after blasting by the conventional blasting scheme is about 1.51-1.69 times that of the smooth blasting.Based on the original formula for calculating the radius of the rupture zone.Calculate the wall pressure value of air-deck charge structure,and considering the secondary expansion of the crack under the effect of the explosion gas,the theoretical calculation formula of the damage range of the surrounding rock of the peripheral hole is obtained.Using LS-DYNA for numerical simulation of air-deck charge explosion,it was found that by changing the axial uncoupling coefficient,the wall pressure of the borehole decreases with the increase of the axial uncoupling coefficient,and the lesion dimensions also decreases.The uncoupling coefficient has an important influence on the extent of damage caused by the blasting of peripheral holes.The axial uncoupling coefficient of 4.0 is used in the actual blasting scheme,and the blasting effect is better.Therefore,the research in this paper has important reference value for the design of blasting parameters.