Effects of grouting in reducing excessive tunnel lining deformation: Field experiment and numerical modelling using material point method

Abstract

Excessive deformation of tunnel lining structures can be identified as a common problem in Eastern China soft ground. Grouting treatment is an effective and common method to actively mitigate excessive cross-sectional deformation of tunnel lining rings in soft soils. However, grouting operations would introduce localized heavy disturbance to the surrounding ground around the grouting nozzles, causing large-deformational soil movement. The occurrence of large soil movement makes it difficult to use traditional finite element methodologies when it comes to modeling the effects of the grouting treatment on tunnel lining structures. To cope with this challenge, this paper proposes a simulation framework based on the Material Point Method, which enables explicit modeling of the grouting injection process and natural incorporation of large deformation. On the other hand, a field experimental study of an operational shield metro tunnel with grouting treatment has been conducted. The experimental study involved an extensive monitoring scheme and various geometrical arrangements of the grouting operation, thus the data from the field monitoring records enable a comprehensive comparison with the numerical results. The comparison between the experimental and numerically simulated results from the grouting treatment shows a satisfactory agreement. A sensitivity analysis of the grouting parameters is then carried out. The results from both the field experiment and numerical simulation show that with the increase of the height and volume of the grout, the recovery effect of the horizontal convergence is improved. However, limiting values of these grout parameters exist, beyond which any further increase would become less effective. The relative positions of the grouting to the tunnel, both horizontally and vertically, also show a sensitive effect.