Study on the Influence of Back-fill Grouting Parameters in Unsaturated Strata on the Seismic Performance of Shield Tunnels

Abstract

In this study, based on unsaturated soil theory, the diffusion behavior of shield tunnel back-fill grouting in unsaturated strata was considered, and Van Genuchten equation was introduced for deriving calculation formula for grouting diffusion radius. Then, an analysis flow for the influence of back-fill grouting parameters on seismic performance of shield tunnel was proposed, and the analysis was carried out with an actual project example. The results show that, compared to the saturated state, owing to the existence of matrix suction in the unsaturated soil, the permeability of the stratum is reduced, resulting in a slower increase in the grouting diffusion radius and smaller ultimate grouting distance. In this project, after using asphalt-cement grouting material, increasing the grouting time and grouting pressure, as well as reducing the elastic modulus of the material can decrease the seismic response of the tunnel. When the grouting time t = 60 min, grouting pressure P0 = 0.5 MPa, elastic modulus E = 49.1 MPa, the seismic-reduction rate of the structure can reach 25.65%. Finally, the fitted equations for the grouting time, pressure, and elastic modulus of the grouting material with the relative displacement and seismic-reduction rate of the tunnel were obtained.