A discrepancy between observed and predicted NATM tunnel behaviors and updating: a case study of the Sabzkuh tunnel
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The 11 km long Sabzkuh water conveyance tunnel is under construction using conventional and tunnel boring machine tunneling techniques in the Zagros Mountains of south west Iran. During excavation of the conventional section (i.e., 350 m), three daylighting collapses occurred in the tunnel, and large sinkholes developed at the ground surface, due to both poor ground conditions and inappropriate selection of excavation and support class (ESC). In this study, the influence of ESC on tunnel response and stability was investigated through three dimensional (3D) finite difference and finite element methods. The analysis results of numerical modeling indicated that the tunnel face would be stable if a single stage (full face) excavation and an advance step of 1.5 m (defined as ESC#1) were applied. However, the reality was different, and the tunnel collapsed soon after the face was only 35 m away from the portal. Having changed the ESC by taking into account new geological and geotechnical data obtained from face mapping, a field survey of surface cavity, and a trench study, the tunneling advance rate was satisfactory (1.5 m/day) despite the many challenges encountered. This paper presents a brief review of some of the key geological challenges faced in the tunnel design, including characterization of the ground conditions, selection of appropriate design parameters, and evaluation of the excavation and support installation sequence based on monitoring and analyzing ground behavior during construction. The discrepancy between the predicted and observed behavior of the tunnel, and some practical considerations, are also discussed.
KeywordsSequential excavation method Fault zone Daylighting collapse Sabzkuh tunnel Numerical method
Many thanks are due to IMN Consulting Engineers and the project manager of the Sabzkuh tunnel, Mr. Ali Asghar Izadi for sharing their experience and guidance with the authors.
- American Society of Civil Engineering (1984) Guidelines for tunnel lining design. In: O’Rourke TD (ed) ASCE technical council on research. Technical Committee on Tunnel Lining Design. American Society of Civil Engineers, New YorkGoogle Scholar
- Carranza-Torres C, Reich T, Saftner D (2013) Stability of shallow circular tunnels in soils using analytical and numerical models. In: Proceedings of the 61st Minnesota annual geotechnical engineering conference, University of MinnesotaGoogle Scholar
- Eftekhari A, Taromi M, Saeidi M (2014) Uncertainties and complexities of the geological model in slope stability: a case study of Sabzkuh tunnel. Int J Min Geo-Eng 48(1):69–79Google Scholar
- Eftekhari A, Taromi M, Saeidi M (2015) A study of the reinforcement effect of IPE Arc Support Technique (IAST)—a case study of Sabzkuh tunnel. J Eng Geol 9(1):2559–2728Google Scholar
- Elyasi A, Javadi M, Moradi T, Moharrami J, Parnian S, Amra M (2015) Numerical modeling of an umbrella arch as a pre-support system in difficult geological conditions: a case study. Bull Eng Geol Environ 75:211–221Google Scholar
- Fairhurst C, Carranza-Torres C (2002) Closing the circle. In: Labuz J, Bentler J (eds) Proceedings of the 50th annual Geotechnical Engineering Conference, MinnesotaGoogle Scholar
- Hoek E, Carranza-Torres C, Diederichs M, Corkum B (2008) Integration of geotechnical and structural design in tunneling. In: Proceedings of 56th Annual Geotechnical Engineering Conference, MinneapolisGoogle Scholar
- Itasca Consulting Group (1997) FLAC3D, fast Lagrangian analysis of continua in 3 dimensions. Version 2.1. MinneapolisGoogle Scholar
- Karami M, Faramarzi L, Bagherpur R, Raisi Gahrooee D (2014) Influence of geological features and geomechanical properties of rock mass on TBM selection for Sabzkuh water conveyance tunnel. J Eng Geol 8(2):2169–2198Google Scholar
- Proctor RV, White TL (1946) Rock tunneling with steel supports. Commercial Shearing, OhioGoogle Scholar