A breakthrough was achieved for a 4.88 km-long tunnel between Shilphata and Ghansoli for the Mumbai-Ahmedabad bullet train project on Saturday morning, the National High Speed Rail Corporation Limited (NHSRCL) said.
Union Railway Minister Ashwini Vaishnaw was present at the Ghansoli shaft when this breakthrough was achieved by way of a controlled blast.
The tunnel, excavated using the New Austrian Tunnel Method (NATM), is part of the 21 km underground stretch between the Bandra-Kurla Complex (BKC) and Shilphata, including a 7 km segment beneath Thane Creek.
With the latest breakthrough, the bullet train tunnel now connects the Savali shaft to the tunnel portal at Shilphata, linking it to the viaduct portion of the Mumbai-Ahmedabad High Speed Rail (MAHSR) project, the NHSRCL stated in a release.
The NHSRCL said that excavation of the tunnel began in May 2024 in three phases, and the first breakthrough of a 2.7 km continuous section was achieved on July 9. An additional intermediate tunnel (ADIT) was built to allow simultaneous excavation from both Ghansoli and Shilphata sides.
The NATM tunnel has an internal width of 12.6 metres and was constructed using drilling, blasting, survey works, and support systems under challenging geological conditions, it stated.
The corporation said that the next phase will involve waterproofing, lining, finishing, and equipment installation, while the remaining 16 km of tunnelling will be executed using tunnel boring machines (TBMs).
The completed tunnel will be a single-tube, 13.1-metre diameter structure accommodating twin tracks for both up and down lines.
The corporation also highlighted comprehensive safety measures, including settlement markers, piezometers, inclinometers, strain gauges and restricted site access, along with arrangements to pump fresh air for workers inside the tunnel.
The 508 km-long Mumbai-Ahmedabad high-speed rail corridor is India's first bullet train project. According to the NHSRCL, work has been completed on 321 km of viaduct, 398 km of pier, along with 17 river bridges, nine steel bridges, and the installation of over four lakh noise barriers across 206 km.
The track bed construction has been finished on 206 km, and more than 2,000 overhead equipment masts have been installed covering 48 km of the mainline viaduct, it stated.
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