Ashwini Vaishnaw inspects under construction undersea tunnel of MAHSR

Mumbai (Maharashtra) [India], January 18 : Minister of Railways Ashwini Vaishnaw visited the Mumbai-Ahmedabad High-Speed Rail site on Saturday. During his visit, the minister inspected a very unique 21 km long underground/undersea tunnel, which is under construction between the Mumbai bullet train underground station at the Bandra-Kurla Complex and Shilphata in Maharashtra.
Out of 21 km of tunnelling works, 16 km is through tunnel boring machines, and the remaining 5 km is through NATM. This also includes 7 km of undersea tunnel at Thane Creek.
On this occasion, talking to the media, Vaishnaw said that there is very good progress and a lot of attention has been paid to safety. Ventilation, lighting, all these things have been taken care of. The construction of the tunnel is going on at a good pace and overall, about 340 km of work on the Mumbai-Ahmedabad High Speed Rail is already in very good progress. The bridges over all the rivers are in very good progress and the progress of all the stations is very good.
The official of National High-Speed Rail Corridor Ltd. (NHSRCL) informed us that construction work has already begun at several locations. A 394-meter-long ADIT (Additionally Driven Intermediate Tunnel) was already completed in May 2024 in a record time of 6 months.
This has facilitated two additional NATM faces for the excavation work in addition to Shilphata. Due to this additional access, 1,111 meters (622 meters towards BKC/N1TM out of 1562 m and 489 meters towards Ahmedabad/N2TA out of 1628 m) of tunnelling work has been achieved.
The ADIT of dimensions 11 meters x 6.4 meters will give direct vehicular access to the main tunnel during construction and operations and may also be used for the evacuation process in an emergency.
It is also informed that Shaft 1 is 36 meters deep at the Mumbai HSR station construction site excavation work, which is currently underway. Shaft 2 at Vikhroli, at a depth of 56 meters, is completed. This shaft will be used to lower two tunnel boring machines in two different directions, one towards BKC and another one towards Ahmedabad. Shaft 3, with a depth of 39 meters, in Savli, has been completed.
Officials informed that the tunnel portal at Shilphata, which is the NATM end of the tunnel, has had portal work that is already completed and 602 meters of tunnel work out of 1628m (N3TM) has been achieved so far.
During the presentation, officials said that all precautionary measures had also been taken to avoid any accidents. They said that sufficient ventilation is being ensured inside the tunnel, ensuring a safe and ventilated workforce inside the tunnel sites.
All excavated material is being disposed of as per the state government's direction. Structures/buildings around the tunnel sites are continuously monitored. Various types of geotechnical instruments, like inclinometers, vibration monitors, ground settlement markers, tilt meters, etc., have been installed at and around construction sites for monitoring tilt, settlement, vibration, cracks and deformation.
These instruments play a crucial role in making sure that there is no risk to ongoing underground works like excavation and tunnelling or to the structures surrounding the site.
It is also pertinent to note that a dedicated casting yard for casting tunnel lining for the 16 km TBM portion is already operational in Mahape. 77,000 segments will be cast to form 7,700 rings. Special ring segments are being cast for the tunnel lining, each ring comprising nine curved segments and one key segment, with each segment being 2 meters wide and 0.5 meters (500 mm) thick.
High-strength M70-grade concrete is being used to ensure superior structural integrity and long-term durability. The casting and stacking yard covers an area of 11.17 ha in Mahape, Thane district, Maharashtra. The yard will feature nine sets of moulds, each containing ten pieces.
The yard is equipped with various cranes, gantries, and machines to automate and mechanise the casting operations, ensuring high-quality assurance during the casting and stacking of the segments. Additionally, the facility will include casting sheds, a stacking area, a batching plant, and a steam curing area.