Study on the preloading effect of grouting on the tunnel lining

Grouting can effectively improve the stress state of the tunnel lining tensile areas under high external water pressure. To determine the relation between the permanent preloading effect and the post-grouting preloading effect on tunnel linings, several groups of grouting experiments were conducted using a grouting simulation test device developed in this research. Theoretical analysis was then performed on the basis of the experiments. Results showed that the preloading effect was severely affected by microcracks in the grouting area, although the effect gradually decreased after grouting. The ratio of the permanent effects against the post-grouting effects was shown to be a function of the drainage volume and deformation of the grouted rock mass.