Analysis of influence and prediction of adjacent foundation pit excavation on tunnel deformation

Abstract

The adjacent foundation pit excavation will cause the deformation of existing tunnel, which will threaten the safety of tunnel operation in serious cases. The existing research lacks comparative research of different projects. Based on the statistical analysis of 42 engineering cases in various regions of China, the influence law that the horizontal and vertical clear distance between the foundation pit and the tunnel on the horizontal and vertical displacement of the tunnel is studied. The actual monitoring values of 10 projects and the calculation results obtained by the two-steps method is compared. It is found that the horizontal displacement of the tunnel decreases with the increase of the horizontal or vertical clear distance between the tunnel and the foundation pit. When the vertical clear distance is positive and large, the tunnel uplifts and when the vertical clear distance is negative and large, the tunnel settles. When the absolute value of vertical clearance is small, the vertical displacement of tunnel has no obvious law. The two-steps method is only applicable to the case that the buried depth of tunnel vault is greater than the excavation depth of foundation pit, and is not applicable to the case that the buried depth of tunnel vault is less than or close to the excavation depth of foundation pit.