Numerical analysis on the effect of grouting treatments on recovering deformed tunnels

Nowadays, super deep and large excavations increase the risks to subsurface utilities in congested urban areas. Under this circumstance, grouting treatments have been proved to be capable of recovering the deformations caused by deep excavations precisely and cost effectively. In this study, field practice of grouting treatment in a metro project in Nanjing is replicated with finite element method, and parametric studies are implemented to explore effective grouting schemes for recovering the deformed tunnels. Various factors such as grouting sequence, initial grouting time, location of grouting columns and tunnels are considered in parametric studies. Along the longitudinal axis of a tunnel, for the observed segment lining, grouting treatments 2.4 m away from the segment lining will generally have minor effect on its horizontal convergences, with the exception that grouting treatments cause comparatively large horizontal displacements. In the direction perpendicular to the longitudinal axis of a tunnel, previous grouting treatments, which are in the rows closer to the tunnel, will impede most influence of subsequent grouting treatments in the rows further away from the tunnel. Generally, the earlier the grouting treatments are activated, the smaller the final excavation-induced horizontal convergences are. Tunnels rotate clockwise in the process of excavations and grouting treatments.