Effect of Grouting Reinforcement on Settlement of Existing Tunnels: Case Study of a New Crossing Underpass

Abstract

In the construction of the new shield tunnels crossing existing tunnels, grouting rings are often installed in the existing tunnels for protection. To study the effect of grouting rings on the settlement of existing tunnels, the variations of soil properties and relevant parameters before and after the grouting are analyzed. By considering the effect of the grouting ring on the reduction of the stress and the reinforcement of the surrounding foundation soil, the stress reduction model of the heterogeneous soil layer and the model of the tunnel settlement calculation are proposed. The formula for the reduction of the stress after passing through the grouting ring is deduced. Moreover, by comprehensively taking the influences of the shield excavation and grouting ring into account, the formula for calculating the vertical displacement of the existing tunnel caused by the excavation of the new tunnel is derived. Further, the impacts of the length and the thickness of the grouting ring on the settlement of the existing tunnel are studied. The results of the theoretical calculation method proposed herein are well consistent with the data computed by the finite element model, and both follow a relatively similar change trend. According to the obtained results, installing the grouting ring on the existing tunnel can effectively reduce the tunnel settlement. Finally, the results demonstrate that increasing the length and the thickness of the grouting ring can strengthen the protection of the existing tunnel, but the effect gradually decreases.