Tunnel Portal Instability Adjoining Landslide Area and Remedial Measures: A Case Study of Sivoke-Rangpo Railway Tunnel T-7

The construction of tunnel portals in hilly terrain or in slope areas often involves difficulties, which are closely related to features, such as slope topography, geology, underneath water, geotechnics, construction geometry and the tunnel excavation method. The initiation of landslides or the acceleration of these actions is one of the main challenges faced during construction of the tunnel portals. In this paper, the instability problems in Sivoke-Rangpo Railway tunnel portal T7- P1 that has been excavated with a thick slope wash material, water charged conditions and complex geological conditions (Phyllite, schist and quarzitic schist) and heavy rainfall in this region have been addressed. The geotechnical investigation carried out to ascertain the rock mass conditions and its geo-mechanical parameters. Micro-pile solutions with permanent anchors designed for slope protection at different levels and installation of deep drainage provisions considered to drain out the underneath water. This case study highlights the sufficient ground investigation, slope support design, appropriate excavation and support sequence, required slope monitoring during and after construction process.