Theoretical analysis on horizontal rectification of tunnel near deep foundation pit by grouting

In a city with crowded underground space, the excavation of deep foundation pit leads to excessive displacement of adjacent subways and tunnels, which poses serious threats to the safety of existing tunnel structures. At present, theoretical analysis of the horizontal displacement rectification of tunnel by compaction grouting near a deep foundation pit is rarely reported. In this study, the analytical solution is derived based on the source-source theory and cavity expansion theory for grouting in a quarter-infinite space with a vertical rigid boundary (i.e. a rigid retaining structure). The horizontal displacement of tunnel can be determined on the basis of the Pasternak foundation beam theory. Then the calculated horizontal displacement of tunnel is validated against the measured results obtained from a tunnel rectification test based on grouting in Tianjin and a rectification engineering in Shenzhen. Based on the theoretical solution proposed in this study, the grouting parameters and modes are optimized to reach a high-efficient rectification. For the single-opening grouting, with the increase of horizontal distance from the grouting tube, the horizontal displacement of soil gets lower and becomes negligible (less than 0.5 mm) at 12 m away from the tube. For the multi-row grouting, the depth of the end of the grouting tube should be reduced for high-efficient rectification.