Technology Research Of City Tunnel Under Complex Environment Construction

Along with the vigorous development of the national traffic and increasingly crowded road traffic, underground transportation has become the main development trend. It is inevitable that the surrounding soil mass is disturbed in the excavation process of city subway tunnel engineering, so the balance of the original must turn to a new balance.And settlement and deformation of ground and surface of the earth must be caused Relative to mountain tunnel, it is more stringent of underground city tunnel construction on the deformation control, the risk of large deformation and collapse is not be allowed as well.This paper bases on Beijing metro line four standby platform engineering. The project has a complex surrounding environment. The shaft is near the existing subway station, the combat readiness car channel is through the Xiaoqing River, Jingmi diversion canal, belonging to south to North Water Transfer Project,and other important engineering and municipal pipeline. The platform of shaft construction in rock strata, adjacent to the existing station, it presents a great challenge to the blasting construction. There is water-abundant sand and cobble layer in part of he combat readiness car channel. And contain much sediment in this stratum. There is no condition for ground precipitation and reinforcement. These all bring great difficulties to the pre-grouting construction. In the condition of confined water,sudden inrush of water and sand is easily appeared when the tunnel is excavated in the condition of confined water. So land subsidence is occurred It brings great risks for construction,surrounding Jingmi diversion, and existing subway station buildings.In view of the complex engineering environment,firstly, a research is carried out in this paper on design of pre-splitting blasting in shaft, which is adjacent to the existing station.A construction scheme is designed for this section projec.But the specific parameters needed be optimized basing on field test explosion.Then Optimization of construction scheme is studied for the tunnel construction which is through water-abundant sand and cobble loose stratum layer. This is the focus of thispaper. The main research of this research is the traditional curtain grouting Inside the cave,horizontal single pipe jet grouting,and water, slurry separated horizontal jet grouting.The paper predicts and analyses tunnel construction scheme optimization and deformation for this section projec using ANSYS software. Based on the results of deformation analysis of monitoring points and stress analysis of the initial supporting structure which is in the process of tunnel excavation, the paper determines the construction method with minimum risk.Finally,the paper predicts and analyses tunnel construction scheme optimization and deformation for which is under the diversion canal using ANSYS software also. Based on the results of deformation analysis of monitoring points and stress analysis of the initial supporting structure which is in the process of tunnel excavation, the paper determines the construction method with minimum risk.This paper is successfully applied in Beijing metro line four standby platform engineering.And practical guide is offered by this paper for construction safety of the tunnel. As well as theoretical basis is provide for future similar engineering construction.