Study On Influence Of Blasting Construction Of Small Span Tunnel On Existing Tunnel

Since the transport capacity of traditional single-track railways cannot meet the needs of fast economic development, the reconstruction of existing single-track railways into double ones can not only improve the transport capacity and efficiency but also save investment, which will definitely propel the railway construction toward a high growing period. During the construction of double-track railways, the vibration caused by the blast of new tunnels will surely have some influence on the structure of nearby existing tunnels, even on their operational safety, for there are different levels of quality defects or diseases resulting from many years operation of the existing tunnels. Consequently, how to make feasible explosion plans, which can ensure both the safety of the existing tunnels and the construction progress of new ones, has become an urgent problem that needs to be solved.based on the second line of Chongqing-Huaihua railway, this paper collects statistics on small-distance tunnels, and selects some typical small-distance tunnels of 5m, 10m, and 15m, and this paper studies the following aspects:(1) Know the main quality defects and types of diseases of the existing Chongqing-Huaihua railway tunnels by nondestructive testing and spot investigation; evaluated their structural conditions and regard them as the basis for differentiated management of small-distance tunnels'blasting work.(2) By using numerical simulation software, analyzed the vibration iMPact of new tunnels'blasting work on existing ones under the conditions of different surrounding rock level, different spacing, excavation footages, excavation methods and maximum charges; analyzed and summarize the particle velocity and the spatial distribution of unit stress of the existing tunnels.(3) Analyzed the factors which influence the strength of blasting vibration, and puted forward measures to reduce it and proposed information construction concept to ensure the safety of existing tunnels and the construction progress and cost of the new ones accordingly.