Study On The Blasting Seismic Effects And Its Control On Railway Roadbed And Slope During Light Rail Tunnel Excavation

With the prosperous development of China’s traffic infrastructure construction, It is imperative to construct expressway and high-speed railway in mountainous areas and hilly regions and also light rail in cities. So the methods of drilling and blasting are widely applied to the excavation of the highway tunnels,railway tunnels and the light rail tunnels. Meanwhile, the blasting seismic effects caused by blasting excavation process are increasingly concerned. This paper is based on the project of Yu Wangling tunnel which is the second stage of Line 1 Rapid Transit in Ningbo. The seismic effects and its control of the railway roadbed and slope caused by tunnel blasting excavation, have been researched through the analysis of the on-the-spot monitoring results and the application of the ANSYS/LS-DYNA dynamic analysis software for numerical simulation analysis, the results of the survey are as follows:Firstly, blasting vibration monitoring and results analysis have been conducted based on the blasting vibration observation projects, which it has been obtained that the light rail tunnel blasting seismic wave propagation and attenuation regularity of Ningbo area. That the attenuation empirical formula of vertical, horizontal radial and horizontal tangential peak particle vibration velocity varies with explosive mass and distance of the relatively close distance from the earth’s surface and the long-distance railway roadbed, has been gotten by analyzing the observation results.Secondly, through the analysis about characteristics of the frequency of the vibration wave and the comparison of the corresponding distance, it was shown that the blasting vibration attenuation indexes of the longer distance are much larger than the shorter distance. Meanwhile, with the distance becomes further this indexes are also enlarged. The main frequencies of the particle vibration velocity on earth’s surface close to blasting area are mainly distributed between 20-30 Hz, while the main frequencies of the particle vibration velocity near railway roadbed further from blasting area are mainly distributed between 10-20 Hz.Thirdly, that the numerical simulation model of the light rail tunnel blasting excavation, has been established, and that the dynamic response analysis of railway roadbed and slope under the influence of the tunnel blasting excavation, has been completed, which shows that, the particle vibration velocity changes and attenuates slowly, and the peak appears relatively late, and horizontal tangential component and the vibration velocity vector fits well, while the location of railway roadbed flushwith the tunnel blasting excavation section. The particle vibration velocity on both sides along the railway roadbed in the central section has certain attenuation under the influence of the distance, while regularity of the attenuation is not obvious.Fourthly,the results of slope dynamic response analysis show that the particle vibration velocity on the slope decays faster, and the peak value of the particle vibration velocity appears earlier, the horizontal tangential component and the vector sum of the vibration velocity fit well. The changes of the characteristic points on different heights of the slope and the peak value of the particle vibration velocity is not significant or obvious with the variation of the height, but it has a significant amplification effect on the slope shoulder.Fifthly,based on the analysis of the blasting vibration safety monitoring and the dynamic response of railway roadbed and slope under the influence of the blasting excavation of the light rail tunnel,it has been proposed that a series of approaches on the engineering geology and the environmental conditions and the construction method and construction technology of relying engineering, which include some methods to control the blasting seismic effects, such as changing the excavation method,choosing the reasonable control blasting excavation,selecting the suitable charge structure, determining the optimal consumption of explosive factor, and controlling reasonably the optimal slots dose and so on.