Analysis and Investigation on the Measured Data of Deformation of Existing Tunnel under the Construction of Side Foundation Pit in the Subway Protection Zone

ABSTRACT The existing tunnel may deform due to side foundation pit engineering, which affects normal use and the safety of the tunnel. Therefore, the control of its deformation is of great importance. Twenty three cases of side foundation pit projects have been summarised and categorised. The empirical prediction model of tunnel deformation is further proposed by exploring the impact of various construction factors on tunnel deformation. Based on the side foundation pit engineering in the subway protection zone, the effectiveness of the prediction model is verified through deformation monitoring of the existing tunnel. The results showed that the influencing factors from large to small are horizontal spacing, foundation pit depth, foundation pit length, and tunnel roof burial depth. An empirical prediction function between the cumulative deformation of the tunnel and the factor variables was established by combining the four major factors. And the pre-control indicators of the side foundation pit were obtained for different deformation limits. It was found that the cumulative deformation is less than the control value through the monitoring of the shield tunnel.