Reasonable Spacing and Vibration Reduction Measure for Tunnel Blasting with Large Section and Small Clear Distance
In the tunnel blasting construction with small clear distance,the rock and soil mass around tunnel deteriorate due to disturbance of multiple blasting,and the bearing capacity of surrounding rock is reduced.At the same time,blasting vibration directly affects the existing tunnel structure to varying degrees of impact even damage,e.g.as lining structure cracking,peeling,etc.Therefore,the reasonable design of tunnel spacing and necessary vibration reduction measures are very important to improve the overall safety performance of tunnel,and to prolong the service performance of tunnel.To study the reasonable spacing of tunnel with different surrounding rock level,taking the small clear distance section of Xizengshan highway tunnel on Yiwu-Dongyang expressway as study background,ANSYS LS-DYNA finite element dynamic analysis program is adopted to establish the 3D numerical model for small clear distance tunnel blasting construction.The vibration response rule of adjacent first-excavation hole is focused under the subsequent hole blasting construction of grade Ⅲ,Ⅳ and Ⅴ surrounding rocks.The internal relations of surrounding rock level,vibration velocity,and tunnel spacing are established.The reasonable spacing is divided according to the vibration velocity limit of lining structure.The application of vibration reduction hole in blasting construction of small spacing tunnel is explored.The test section is selected to carry out the vibration monitoring of first-excavation hole,and the evaluate the vibration reduction effect.The result indicates that the vibration velocity value of side wall of blasting side of first-excavation hole is the largest.Based on this,the reasonable tunnel spacing of surrounding rock of grade Ⅲ,Ⅳ and Ⅴ is 5.8,8.2,11.1 m respectively.When the spacing is less than above values,the monitoring should be strengthened,and the corresponding vibration reduction and reinforcement measures should be taken.After the damping hole is arranged in the subsequent hole,the calculated value of vibration velocity and the monitored value increase by 18.7%and 32.6%respectively,indicating that the effect of damping hole is obvious.The maximum value of vibration velocity is 3.49 cm/s,which is far less than the limit value of 7cm/s.The vibration velocity of secondary lining of first-excavation hole meets the safety control requirements.
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