Breakthrough in T-8 tunnel brings Sikkim closer to rail connectivity

GANGTOK,: Another tunnel of the Sevok-Rangpo Rail Project (SRRP) achieved a breakthrough on Wednesday, marking a significant milestone in the construction of the railway line linking Sikkim with the rest of the country.

The breakthrough was achieved in the 4,148.6-metre-long Tunnel T-8 located in West Bengal’s Kalimpong district in the presence of SRRP advisor Mohinder Singh, chief general manager and project coordinator Renya Ete and officials of IRCON International Limited, along with representatives from design consultant Amberg Engineering, construction agency APCO Infratech Pvt Ltd and local administration.

According to a press release, the tunnel is located between Teesta Bazar and Melli Bazar in Kalimpong district. The project also includes a 1,010-metre evacuation (emergency) tunnel connecting the main tunnel to National Highway-10, which had been completed earlier.

Tunnel T-8 passes through vulnerable and challenging geological and seismic conditions of the Lesser Himalayas and is considered the most critical tunnel of the project.

Like other tunnels in the project, the latest tunnelling technology, New Austrian Tunnelling Method (NATM), has been adopted. Swiss consultancy Amberg Engineering designed the tunnel, while the execution team comprises experienced engineers from India, officials said.

The tunnelling work was awarded to APCO Infratech Pvt Ltd in January 2020. However, construction was severely hampered for over six months following the outbreak of the COVID-19 pandemic and the subsequent lockdowns. Mining work eventually began in January 2021.

During excavation, the team faced severe squeezing and water seepage issues, but continued operations using advanced technologies such as Tunnel Seismic Prediction (TSP) to assess ground conditions ahead of mining.

Officials said that completing over 4 km of tunnelling, including about 1 km of evacuation tunnel, within five years despite challenges such as the pandemic, difficult geological conditions and disruptions along NH-10 was a major achievement.

The 45-km-long railway line connecting Sevok in West Bengal to Rangpo in Sikkim comprises 14 tunnels, 15 major bridges and five stations. About 38.68 km of the alignment passes through tunnels.

With the completion of mining in Tunnel T-8, tunnelling work in 13 of the 14 tunnels has been completed. Only about 415 metres of excavation remains in Tunnel T-10, the longest tunnel of the project.

Officials said lining work has been completed in 32.4 km across 12 tunnels, while ballastless track has been laid over 21 km inside the tunnels.

The Sevok-Rangpo rail line is considered a prestigious national project of strategic importance. Once completed, it will connect Sikkim to the country’s railway network for the first time.

Construction of station yards and track linking work is currently underway on a fast-track basis, with the first phase of the project targeted for completion by December 2027.

In the second phase, the railway line will be extended from Rangpo to Gangtok.