The Tunnel Construction Method Of Shallow Tunnel With Large Cross-section In Nanfan Section Of Changchun Metro Line

In the underground tunnel construction process,the disturbance of the formation makes the original state of soilunbalanced and affects the settlement and convergence of the tunnel.The interval tunnel in the construction must be strictly controlled settlement,to prevent collapse for the purpose.If it covers the shallow soil areas,and the soil of poor stability,the excavation can easily lead to landslides,gushing water,surface subsidence,etc.,resulting in ground collapse.The consolidation of the surrounding rock arch control is important to ensure the safety of overburden soil in the Construction.In order to ensure the safety and stability of the tunnel construction,measures such as well point precipitation or pre-reinforcement and water plugging in the tunnel are generally used to provide favorable conditions for the subway construction.Before the construction of the large section of the parking line,the quasi-section near the left line has been excavated.Therefore,aiming at the complicated engineering conditions of Nanfan District of Changchun Subway Line 1,the following conclusions are drawn;1.According to engineering geological conditions,hydrogeological conditions and the project's own risk source analysis,confirm the impact of large section of shallow overburden,underground pipelines,and adjacent standard segments as the main source of risk for the project;2.Through the engineering analogy of the construction method,determine the excavation construction of the large section excavation using the double sidewall guide tunneling method.According to the risk source of the large and shallow overburden soil section,take the section arch pipe shed for reinforcement.The diameter of the pipe shed is 180 mm.150 degrees range setting,tube spacing 40 mm,extrapolation angle 1 degrees,pipe shed divided into 3 sections,each length of about60m;3.According to the site's existing technical conditions and similar engineering experience,the reinforcement measures for deep hole grouting under the pipeline are determined,the circumferential reinforcement arch part is 150 degrees,the single cycle length 5m or 10 m of the advanced deep hole grouting(refer to the pipeline type),the slurry uses cement water glass double liquid slurry and the grouting hole diffusion radius 0.8m;4.During the construction process,monitoring projects such as surface subsidence,pipeline subsidence,dome settlement,and section convergence were carried out.Through the monitoring data,the safety and stability of the construction method was analyzed,a complete monitoring measurement monitoring system was established,and the monitoring data was fed back in time.Guide construction;5.During the construction process,the abnormal surface settlement and abnormal deformation of the K23 + 155 section are fed back through the monitoring data.Immediately,the closed face is closed,the construction is suspended,the monitoringfrequency is increased,and simultaneously carry out I-beam reinforcement in corresponding positions in the hole.In addition,radial grouting and other measures are taken to effectively control the deformation anomaly.Once the data is stable,the construction is again organized.This project conducts research on various existing risk factors,determines control measures for each risk factor,formulates construction parameters,ensures the safety and stability of the structure and the surrounding environment,and ensures the progress,safety,and quality.