Influence of grouting on rehabilitation of an over-deformed operating shield tunnel lining in soft clay

A number of shield tunnels in soft clay often undergo large deformation during their service life especially when subjected to nearby engineering activities. The grouting on two sides of a tunnel springline has proved effective in not only controlling further deformation but also in reducing existing large deformations. This paper presents a case-based analysis of the effect of this kind of grouting treatment on reducing tunnel deformation by both field measurement and numerical modeling. The field measurement of tunnel convergence during the grouting procedure indicates that an average of 25% of the original large convergence area could be reduced. The proposed three-dimensional numerical model incorporates the internal pressure method to simulate the grouting and is validated by the field measurement results showing reduction in tunnel convergence. Moreover, the reduction in segmental joint openings is also derived from numerical simulations. However, the effect of grouting is unfavorably negative on the dislocation of any joint near the springline. Hence, a sensitive study on grouting parameters in terms of the grouting sequence for multiple rows and the grouting distance between tunnel and injection holes was carried out. A symmetrical grouting on two sides of the tunnel springline following a sequential move to the tunnel of no less than 3.0 m in distance was found to be the best option for grouting in practice given the ground conditions in the study area.