World’s longest and deepest rail tunnel, the Gotthard Base Tunnel came into function on 2016.The main aim was to shift the traffic volume from roads to train, thereby reducing road accidents and environmental hazard caused by the heavy trucks. Various engineering risk assessment were done before the construction took place. One of the major risk was geological and hydrological conditions which occured at a depth of approximately 2500 metres below the earth’s surface (Ehrbar and Heinz 2011, 2). According to geological investigations, the feasibility of the project was threatened by two zones: i) the Faido section the Piora syncline; and ii)in the area of the Sedrun intermediate heading, the Tavetsch intermediate line as well as the neighbouring Clavaniev zone to the north, and the Urseren-Gavera zone to the south . Brittle faults are situated in the pre-existing ductile Urseren-Gavera zones.
Microstructure of these faults explains a reverse deformation history from ductile to brittle conditions up to the end of fault. At Piora basin a funnel shaped formation reach n sugar grained dolomite and water reached deep into the rock resulting in loose grain of rock. The road was flooded when a thick jet of water containing dolomite shot out of the mountain (The dreaded Piora basin 2008).Rockfalls occurred during its construction which delayed the work for months. In some section the mountain pressure was so high (Ehrbar and Heinz 2008, 1) that conventional method of excavating the cross section was of no use. This pressure gave the mountain the opportunity to “let of stream”-the more it deforms, the more is the pressure thus, requiring a counterforce to stop the cavity from reclosing. Various advance explorations should be done and due care must be taken as the geological risk cannot be eliminated completely.
Ehrbar, Heinz, and Chief Construction Officer. "Gotthard Base Tunnel Risk Management for the World's Longest Railway Tunnel: Lessons Learnt." In Proceedings of the 37th ITA-AITES World Tunnel Congress. 2011
Ehrbar, Heinz. "Gotthard base tunnel, Switzerland. Experiences with different tunnelling methods." In Proc. 2º Congresso Brasileiro de Túneis e Estruturas Subterrâneas, Sao Paulo. 2008
The dreaded Piora basin.2008.https://www.herrenknecht.com/en/references/referencesdetail/gotthard-base-tunnel/
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