Study on 3D Deformational Characteristics of Shield Tunnel Caused by Neighboring Construction
Date Issued
2012
Date
2012
Author(s)
Wu, Zong-Han
Abstract
Most underground network of Taipei Mass Rapid Transit (MRT) System was composed of shield tunnel. As MRT lines increase and lands decrease in Taipei megalopolis, more and more constructions such as foundation-excavation approach existing shield tunnel closely, and the kind of situations is called neighboring construction. Neighboring construction might threaten the safety of MRT operation and tunnel structure, and therefore has become an issue which is emphasized gradually during these decades.
Conventional tunnel monitoring items are applied popularly in shield tunnel during neighboring construction, such as convergence deformation or railroad settlement, which neglects longitudinal mechanical properties of tunnel. These current methods are established in two-dimensional plane (in-plane). However, neighboring construction is complicated and belongs in three-dimensional phenomenon, thus current methods of tunnel monitoring are inadequate and should be improved.
First of all, this study builds up numerical models of shield tunnel and deep excavation separately by FLAC3D, and the models have been verified by comparing its calculated results with existing analytical solutions and actual case data. The second, this study combines two models into one model for simulating the responses of a shield tunnel encountering neighboring construction. Based on the neighboring construction model, the three-dimensional deformation and stress increment of whole tunnel and specific profile can be discussed in the views of in-plane analysis as well as out-of-plane analysis.
Results of numerical simulation indicate that neighboring construction has a significant influence on three-dimensional deformation and stress variation of shield tunnel. In the part of segment deformation, the deformation of segment center is more than convergence deformation generally, and there is longitudinal deformation between segments. With the distribution of critical failure line, the potential failure site of shield tunnel which is caused by neighboring construction could be a three-dimensional distribution. In the part of stress increment, as a result of out-of-plane analysis, the longitudinal force of shield tunnel would be compressed or tensile along the axial direction, and the appearance of variation may cause damage to tunnel structure which is fragile. Accordingly, this study recommends that more appropriate tunnel monitoring method should be developed in the future, and it might be a better way to evaluate shield tunnel with three-dimensional concept so that provide early warning for tunnel safety.
Subjects
neighboring construction
shield tunnel
three-dimensional deformation
numerical analysis
Type
thesis
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