The smooth blasting technology is the main means to control the over excavation and under excavation of tunnels at present.In order to explore the influence of the charge structure and charge amount of peripheral holes on the blasting effect,a series of single hole blasting tests were conducted in the silty shale section of Wulong Tun-nel.The results show that the best blasting effect for detonating cord initiation can be achieved when a decked pe-ripheral hole is charged with 0.1+0.075 5 kg of explosive.At this time,the residual rate of peripheral holes is 96％,and the average linear overbreak is 15.3 cm.On the other hand,the best blasting effect for detonator initiation happens when the charge amount of a peripheral hole is 0.45 kg,with the residual rate of peripheral holes as 90％and the average linear overbreak as 18.4cm.When a continuous charging structure is adopted for the peripheral holes,the best blasting effect appears as the charging amount is 0.3/0.45 kg.In this case,the residual rate of sur-rounding holes is 32％and the average linear over excavation amount is 24 cm.The decking charge structure of the peripheral holes can effectively improve the blasting effect,which ensures the residual rate of peripheral holes is more than 50％and reduces the tunnel over-excavation.By comparison,the blasting effect,in the order from best to worst,is ranked as detonating cord with decking,detonator with decking and continuous charge,respectively.And their re-sidual rates of peripheral holes are more than 90％,more than 70％,and less than 50％,respectively.It is proved that both the detonating cord with decking charge structure and the detonator with decking charge structure can be used for surrounding holes to control tunnel over-excavation.
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