Abstract #
This paper outlines the methodology for designing the primary and secondary linings of tunnels using the New Austrian Tunnelling Method (NATM). The study focuses on the excavation of two tunnel tubes in Prague, Czech Republic, and details the application of the Finite Element Method (FEM) for analyzing the stress and deformation states in the rock mass during excavation. The analysis also examines the influence zone around the tunnels, predicting the settlement trough and its impact on existing surface structures and utility networks. The study provides critical insights into the geotechnical and structural challenges encountered in urban tunnelling projects.
Technical Relevance #
This document is essential for geotechnical and structural engineers involved in tunnel design and construction, particularly those utilizing the NATM. The detailed analysis of tunnel lining behavior under varying geological conditions and the assessment of the influence zone provide valuable information for ensuring the safety and stability of underground structures in urban environments.
Target Audience #
The document is intended for geotechnical engineers, civil engineers, structural engineers, and professionals involved in tunnel construction and design. It is particularly relevant for those working on projects in densely populated areas where the interaction between the underground structure and the overburden must be carefully managed.
Software and Methodology #
The study employs the GEO4 FEM software to model the tunnel excavation and the behavior of the tunnel lining. The methodology includes the use of isoparametric elements in a 2D plane strain model, with the rock mass modeled as an elasto-plastic material using the Mohr-Coulomb criterion. The analysis focuses on the sequential excavation process, the activation of temporary linings, and the prediction of settlements within the influence zone. The study also considers the effects of jet grouting and anchored retaining walls in stabilizing the surrounding soil and minimizing the impact on surface structures.
Process Description #
The paper begins with an introduction to the project location and the geological conditions along the tunnel route in Prague. It then details the design assumptions for the primary and secondary tunnel linings, including the selection of NATM as the excavation method. The process description covers the FEM analysis used to predict the deformation and stress states in the rock mass during excavation. The study includes an evaluation of the influence zone, predicting the extent of the settlement trough and its impact on surface buildings and utility networks. Diagrams illustrating the excavation sequence and the placement of support structures are provided to enhance understanding.
Main Findings #
The study finds that the use of NATM, combined with the application of jet grouting and anchored retaining walls, is effective in controlling the settlement trough and minimizing the impact on surface structures. The FEM analysis shows that the influence zone extends up to 40 meters from the tunnel centerline, with maximum surface settlements reaching approximately 60mm. The results highlight the importance of considering the influence zone in tunnel design to ensure the safety of both the underground structure and the overburden.
Practical Applications #
The findings from this study are directly applicable to the design and construction of tunnels in urban areas. Engineers can use the insights gained to improve their approach to tunnel lining design, ensuring that the influence zone is adequately managed to prevent damage to surface structures. The study also provides practical guidance on the use of FEM for simulating complex geotechnical interactions during tunnel excavation.
Limitations and Considerations #
The document acknowledges that the results are based on specific geological conditions found along the tunnel route in Prague. Engineers should conduct site-specific analyses to ensure that the influence zone is accurately predicted for other projects. The study also emphasizes the need for continuous geotechnical monitoring during construction to validate the predictions made by the FEM analysis and adjust the design as necessary.
Conclusions #
The paper concludes that the design methodology used for the primary and secondary tunnel linings, incorporating NATM and FEM analysis, is effective in managing the influence zone and ensuring the stability of the tunnel and the overburden. The study highlights the importance of using advanced geotechnical analysis tools in urban tunnelling projects to prevent excessive settlements and protect existing structures. The results demonstrate the viability of the proposed design methodology and its potential application to similar tunnelling projects worldwide.
Related Resources #
Further reading includes studies on the application of NATM in other urban tunnelling projects, research on the use of FEM in geotechnical engineering, and case studies on the management of influence zones in tunnel construction. Additional resources on the design of tunnel linings and the mitigation of settlement troughs can provide deeper insights into optimizing tunnel construction strategies.
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