Dwivedi , R. D. (2024) A Case Study of Tunnel Stability in Quaternary Deposits Using Pipe Roof Supports. Indian Geotechnical Journal.
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In numerical modeling, boundary conditions play a vital role for stability analysis of a tunnel. The top boundary is kept free to simulate vertical movement of material during tunnel excavation in case of a tunnel being excavated at shallow depth through soil like material. On the other hand, the top boundary is kept restricted in case of a deep tunnel. In this view, it becomes important so as to categorize the tunnel as shallow or deep while designing support system for a tunnel. The present paper is a case study which has been carried out for the execution of a part of a railway tunnel being excavated through quaternary deposits below 40–60 m of overburden in Rishikesh–Karnaprayag rail link project in Himalayan region, India. Crown Stability of a tunnel is essential for better re-distribution of induced stresses around the tunnel periphery and the surrounding ground so as to attain a stable equilibrium stage of stresses. The inlet tunnel portals of the Main and Escape tunnel were forced to locate on river-borne material due to constraints related to the geometry of Railway line, its curve and elevation. Large displacements are usually associated with tunnelling through such a kind of loosened and highly weathered rock mass, which could result in settlement of the ground surface. However, other parameters such as shape and size of the tunnel, height of overburden material and consistency of the material which may also result in ground subsidence. The adopted support system for stability of the arched portion of tunnel was modeled in the form of Pipe-roofs which are pre-excavation supports generally installed from crown to the spring levels. The paper describes a methodology of pipe-roof design and the behavior of ground monitored with the help of tunnel instrumentation to validate the efficacy of the installed supports. The study reveals that the pre-excavation support behaves as an arch beam throughout the tunnel's perimeter which enhances the stability of the surrounding ground beyond the formed arch beam, multifold. The Analysis leads for the determination of shallow and deep tunnel based on a limiting value of overburden observed through numerical analysis compared with monitoring results of ground deformations, above that overburden value the tunnel behaves as deep and below the given value, the tunnel behaves as a shallow tunnel.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | Pipe-roof Numerical modeling Soft rock tunnelling Deep tunnel Shallow tunnel |
| Subjects: | Blasting |
| Divisions: | UNSPECIFIED |
| Depositing User: | Mr. B. R. Panduranga |
| Date Deposited: | 10 Apr 2024 04:25 |
| Last Modified: | 10 Apr 2024 04:25 |
| URI: | http://cimfr.csircentral.net/id/eprint/2728 |
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