Study On The Key Technology Of One Over Cross Close-spaced Tunnel Of Shangdao Railway Project

With the growth of the national economy, comprehensive development of underground space utilization increased, large amount of close-spaced construction problems about tunnel and underground projects emerge. At present, a lot of close-spaced construction base on summary of theoretical research, survey strong, but the practice ability. So it is necessary to target specific close-spaced type to make specific construction plan, in order to provide experience and guidance for the later similar projects’safety construction.The paper based on the fact of one over cross close-spaced tunnel of Shangdao railway project, use the basic theory and numerical simulation to analysis the cross near engineering, such as analysis rock mechanics, stress, Terzaghi theory, analysis the new over cross close-spaced construction excavation method, and the influence scope and characteristics of the blasting excavation on existing tunnel. Finally obtain the main results and conclusions by the following:1. Due to new over cross close-spaced construction unloading effect, below existing tunnel upward deformation, lateral pressure becomes larger, vault and floor will be upward deformation. And through the in-situ stress filed, Terzaghi theory and FLAC3D for numerical simulation to get the new tunnel and the existing tunnel interaction range, as the radius25m. According to the theoretical analysis and numerical simulation of the influence scope, determine the cross near engineering across adjacent influence range for25m, and take it as the effect range of the tunnel excavation design and numerical simulation analysis. According to the engineering characteristics, gives a new crossing tunnel construction countermeasure.2. According to the cross near engineering characteristics, developed the tunnel blasting excavation scheme about short bench controlled blasting and excavation machinery combination, up the steps use weak blasting construction in advance, down the steps use mechanical cutting excavation, and set damping hole in mechanical cutting excavation area, to reduce the blasting impact load’s impact on the existing tunnel structure. And identify a new tunnel excavation by blasting parameters. 3. According to the actual condition of new tunnel, use FLAC3D to simulate the most dangerous section, according the tunnel excavation sequence, with the new tunnel’s working area constant close to the existing tunnel, and then away from the process, take the distances between the new tunnel and the existing tunnel as-25m,-15m,-5m,0m,5m,15m,25m, a total of seven point. According to the whole section method and short bench method, do14simulations of tunnel excavation with each method, and calculate the vibration velocity of the existing tunnel’s vault particle. Simulation results verify the feasibility of short bench blasting method, further accurate over cross tunnel construction influence range, as the radius15m; by changing the single hole charge in the two net distance to the nearest section, simulate the different load of blasting excavation on existing tunnel effect, and obtained the two tunnel net distance, single segment of detonating charge and the relation of the existing tunnel vault particle vibration velocity, and establish the blasting vibration prediction model.