Research On Blasting Control Technology In The Approach Construction Of Upper-span Railway Tunnels

With the development of the railway industry in our country,more and more new railway projects are under construction.Due to the influence of geology,topography and other factors,the designed distance between the new tunnel and the existing tunnel is relatively short,which leads to the destruction of the existing tunnel structure and the problems affecting operational safety from time to time.Especially the blasting control problem in the construction of close proximity is gradually becoming a hot and difficult issue in academia and engineering field,which has important practical significance and theoretical value.In this paper,Xiamen North New Liu Tong 1 tunnel across the existing Liu Tong tunnel project as the background,field monitoring was carried out during the whole construction process.At the same time,a series of numerical simulations are carried out on FLAC3D numerical platform,with emphasis on lining response of existing Liutang tunnel.The main research results are as follows.(1)The impact of blasting position on the vibration effect is obvious,and the vibration effect on the blasting side is obviously smaller than that on the blast side;In a wide range of distances to try to use a single function to fit the law of maximum vibration attenuation is not appropriate,according to the largest single-segment dose classification fitting better;Based on the Sadofsky formula,the regression analysis was performed on the monitoring data of the existing tunnel vaults and sidewalls in the upper span of blasting operation.The value of the vault a was larger than the normative values and the value of the wall K was smaller;New tunnel to adopt mechanical/blasting mixed excavation program instead of face dug Blasting construction method effectively reduces the impact of blasting vibration on the existing tunnel.(2)Based on the LS-DYNA single-hole refinement simulation,a method of applying pt time-history curve to the small contour line of the face of the palm in sequence is proposed,which can reduce the computational workload and improve the blasting near and far area vibration effect analysis accuracy.(3)Applying the above loading method,the numerical simulation of mechanized/blasting mixed blasting is carried out,the results show that:Among the vibration velocities in the three'directions,the vibration velocity in the z directio'n is substantially the largest;The closer the location of blasting is to the cross section,the larger the vibration speed of the monitoring points of the existing cross-section of the tunnel;Vault and the side of the vaulted arch vibration speed greater than other locations;The existing tunnel vault and arch lumbar vibration speed is much larger than the side wall,side wall vibration speed is much larger than the arch bottom.(4)Assuming the abolition of mechanical/drilling and blasting excavation program to replace the face of the face blasting construction method,the existing tunnel peak velocity of 7.73cm/s,far exceeding the limit,which indicates the validity of mechanical excavation instead of cutting blasting construction.