Numerical Simulation Analysis Of Large-span Tunnel Excauation And Blasting On The Inluence Of Surface Subsidence

Drill and Blast Method is mostly used as one of construction methods in large-span and shallow-buried tunnel. Surface subsidence and deformation in the process of excavation and blast has a major influence on surface buildings. In order to ensure the continual tunnel construction and the safety of surrounding buildings, mechanical analysis of tunnel construction process and prediction of surface subsidence&deformation in the process of excavation and blast was carried out in this paper. Meanwhile, research on proper tunnel excavation methods would exert a great socioeconomic impact.On the basis of collection and retrieve of massive relative literature, in-depth research on surface subsidence caused by tunnel excavation and blast was made in this paper. Set in Li Jiachong tunnel project,3D finite difference analytical software FLAC3D was adopted to establish model of tunnel excavation process and the factors that affect surface subsidence such as excavation cross-section, surface and buried depth of tunnel were discussed. At the same time, taking consideration into high-voltage iron tower on surface, the paper analyzed the influence of blast on it. And then, numerical simulation data was compared with field data and the paper concluded the law of influence of excavation and blast on surface subsidence in Li Jiachong tunnel. At last, pragmatic control measures of surface subsidence were suggested according to the engineering practice. The conclusion in this paper states as follows:(1) The numerical simulation results of surface subsidence under construction in Li Jiachong tunnel basically coincide with field monitoring results, which states that analytical results in this paper are of a good reliability.(2) Two different simulation methods, Three-bench Seven-step Excavation Method and Twin Side Excavation Method respectively, are adopted in the paper and the conclusion indicates that the maximum surface subsidence by use of Three-bench Seven-step Excavation Method, whose value is2.35mm, was found in tunnel excavation midline and Twin Side Excavation Method can effectively decrease the surface subsidence, and its subsidence value is1.54mm.(3) Redistribution of stress-strain state around the laneway caused by concussion of blast increases surface subsidence to some extent. Surface particle vibrating velocity is relative with distance to tunnel excavation midline. The conclusion states that the shorter the distance from particle to excavation midline is, the higher the particle vibrating velocity is and vice versa. From the results, the particle in iron tower foundation is within the safety vibrating scope, and therefore single blast would not influence tower foundation significantly. However, Three-bench Seven-step Excavation Method was adopted in the project, under which condition multiple circulation blast occurred in the tunnel, and consequently reinforcement measures of iron tower foundation should be used to ensure the safety of tower foundation.