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.
Highlights
With the rapid development of the subway lines of cities, it is highly probable that a new tunnel will cross the existing subway lines in close proximity during the construction process [1,2]
In order to verify the reliability of the developed model, this paper regards a new tunnel running vertically through the existing tunnel as a study case, in which the lower part of the existing tunnel is protected by a grouting ring
Figure99shows showsthe thecloud clouddiagram diagramofof the byby thethe finite element model before andand afterafter setting up thetunnel tunneldisplacement displacementcomputed computed finite element model before setting the grouting ring
Summary
With the rapid development of the subway lines of cities, it is highly probable that a new tunnel will cross the existing subway lines in close proximity during the construction process [1,2]. It is vital to study the protective measures and deformation mechanism of the existing tunnels caused by building new tunnels. There is no theoretical calculation method to examine the effect of the grouting rings on controlling the settlement of the existing tunnels. It is necessary to develop a mechanical model of old and new tunnels under the influence of grouting rings and develop a theoretical method to study the effect of grouting rings on controlling the vertical deformation of existing tunnels. The formula for calculating the vertical displacement of existing tunnels caused by the excavation of new tunnels is deduced by considering a variety of factors affected by the excavation of shield structures. The effects of the length (L) and thickness (t) of the grouting rings on controlling the settlement of the existing tunnel are studied
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