Investigation of Ultraclose Jet Grouting on Existing Cable Tunnel: Field Monitoring and Analytical Insights

Abstract Ultraclose jet grouting (JG) inevitably induces significant disturbances to adjacent infrastructure, such as tunnels. However, there is a lack of high-quality field monitoring data and analytical models for investigating such short-distance interactions. In this study, field measurements were first conducted to examine the vertical deformation behavior of an existing cable tunnel subject to ultraclose JG. Then, an analytical model informed by the monitoring results was proposed to investigate the multimodal deformation behavior and force redistribution in the cable tunnel. In addition, the associated grouting-soil-tunnel interactions and construction recommendations were discussed, and four spatial zonations of tunnel responses due to JG were presented. The key findings are as follows: (1) In the later stages of double-fluid JG, clogging or discontinuous operations easily cause pronounced cyclic uplift–settlement deformation of the tunnel. Single JG column installation can induce a maximum tunnel uplift of nearly 9 mm, and up to 60% of the induced maximum heave may remain after completion; (2) Differences in horizontal and vertical deformation within the tunnel cross section lead to significant tunnel torsion, with the variation in vertical deformation being the dominant factor that determines the direction of torsion. Horizontal deformation dissipates more rapidly with depth beyond the grouting range and laterally compared to vertical deformation. (3) Construction sequences and abnormal working conditions during JG are the most critical factors influencing tunnel deformation, and a higher grouting viscosity tends to reduce the tunnel deformation.