Analysis on the influence of excavation close-range foundation pit on existing tunnel

Abstract

The development of underground space has resulted in a number of neighboring excavation projects, especially the excavation of the foundation pit that span existing subway tunnels. While facing the risk of excavation of the foundation pit crossing tunnel are not only faced with the risks of itself, but also the safety of the existing tunnel is always the serious and difficult problems in the engineering field. This paper takes the foundation pit project of the existing subway tunnel of Jinan as the background. The minimum distance between the pit bottom of the access line and the tunnel is only 1.8m, and the direction of the foundation pit is 15°from the tunnel, it’s close to parallel. Unloading of foundation pit is boned to cause the deformation of inferior tunnel. In order to study the influence of the existing tunnel, we carry out numerical simulation by the finite element software Midas GTS/NX to study the displacement field and stress field of tunnel under the condition of excavation of foundation pit. We study the measures of reinforcement based on the results and further analyse the results of reinforcement. At the same time, we combine an site monitoring data to confirm the effect of reinforcement. Preliminary analyses shows that the excavation of foundation pit has little influence on the horizontal displacement of tunnel and has great influence on vertical displacement. Without reinforcement measures, the uplift of the tunnel reaches 23.11 mm, which exceeds the requirement of deformation control. By grouting the soil between the foundation pit and the tunnel and loading it at the bottom of the tunnel, the uplift of the tunnel is reduced to 4.86 mm, which is consistent with the field measured data, and the reinforcement effect is remarkable. In order to reduce the safety risk, it is necessary to take relevant protection measures in similar projects.