India's first undersea railway tunnel! A tender has been issued for India's first undersea tunnel by the National High Speed Rail Corporation Limited (NHSRCL) as part of the Mumbai-Ahmedabad bullet train project, according to a ToI report. The tunnel is part of the country's first bullet train corridor, linking Mumbai to Ahmedabad. The recently-released tender is for the development of tunnelling works. This includes testing as well as commissioning for double-line high speed railway for the project using tunnel boring machine (TBM) and a new Austrian tunnelling method (NATM). The tender demands the work be completed within a duration of 3.5 years (1,280 days). The report further stated that a geo-technical investigation of the undersea tunnel area was carried out last year by a team of engineers from NHSRCL, RITES and Japan's Kawasaki Geological Engineering firm. In order to study the seabed structure, a static refraction technique (SRT) survey was carried out by the team, which involved firing a high energy sound wave towards the seabed from below the water surface as well as mapping the refracted sound wave in order to determine the density of the rock under the sea bed. The team submitted the final report last year. India's first undersea railway tunnel: All you want to know The bullet train project will have a 21 kilometres long underground corridor from BKC to Kalyan Shilphata in the state of Maharashtra. Around 7 kilometres of this underground corridor is under the Thane creek. Of this, 1.8 km long section will be developed under the sea bed, while the remaining part of the stretch is to be built under the mangroves marshland on either side of the creek, the report said. According to an NHSRCL official who was quoted in the report, for the implementation of this project, all clearances related to the environment from the respective authorities have either been received or authorities have primarily agreed for the approval. The corridor for Mumbai-Ahmedabad bullet train will be 508 km long. With a speed of 320 kmph, the bullet train is expected to complete a journey between Mumbai and Ahmedabad in just around two hours. At present, it takes around seven hours to complete a train journey between these two cities. The bullet train journey will cover a total of 12 stations- Bandra Kurla Complex, Thane, Boisar, Virar, Vapi, Surat, Bilimora, Bharuch, Sabarmati, Baroda, Anand and Ahmedabad railway stations. The development work of this project is likely to get over by 2022-2023.