NHSRCL team after achieving the third mountain tunnel breakthrough in the bullet train project (Express photo/Special arrangement).The Mumbai-Ahmedabad High-Speed Rail (MAHSR) corridor, India’s first bullet train project, achieved a major breakthrough at its third mountain tunnel (and fourth tunnel overall) in Maharashtra’s Palghar district Tuesday. This marks a critical milestone for the project, as these mountain tunnels are among the most challenging stretches of the entire 508-km corridor.The mountain tunnel number 7 (MT-7) is situated between Vapi and Boisar stations, measuring 417 metres in length and 14 metres in width. Officials said the breakthrough was achieved in Ambesari village in Dahanu taluka of Palghar district. Earlier, breakthroughs were achieved at tunnels 8 and 6 between the Vapi and Boisar stations.A tunnel breakthrough occurs when excavation carried out from opposite ends finally connects, marking the successful completion of the structural work.“The excavation was carried out using the controlled drilling and blasting method from both ends. Advanced monitoring systems and geotechnical instruments were deployed throughout the excavation process to ensure structural stability and safety,” said an official of National High Speed Rail Corporation Limited (NHSRCL), the implementing agency of the project.Tunnels account for 27.4 km in the bullet train project. This includes 21 km of underground tunnels, with the remaining 6.4 km comprised of surface tunnels. The surface tunnels feature eight mountain tunnels; seven of these are located in Palghar, Maharashtra, covering a distance of 6.05 km, while one tunnel, measuring 350 metres, is in Gujarat.Also Read | Heated to 45°C and soaked for 3 days: Inside India’s Bullet train track slab factory in SuratThe official further said that real-time monitoring systems, including Surface Settlement Points (SSP), 3D targets, strain gauges, and seismographs, were installed to continuously monitor vibrations, tunnel behaviour, and nearby structures during excavation activities.Officials said that tunnels MT-4, MT-3, MT-2, and MT-1 are making significant progress, with MT-4 nearing 60 per cent completion, MT-3 exceeding 80 per cent excavation, and the other two tunnels progressing steadily.Story continues below this adThe bullet train project covers 352 km in Gujarat and Dadra and Nagar Haveli, and 156 km in Maharashtra. As of March 2026, the project achieved 68.19 per cent physical progress in Gujarat and 40.66 per cent progress in Maharashtra.The first section of the bullet train project from Surat to Bilimora in Gujarat is scheduled to be ready by August 15, 2027. The entire 508-km project is expected to be completed by December 2029.Dheeraj Mishra is a Principal Correspondent with the Business Bureau of The Indian Express. He plays a critical role in covering India's massive infrastructure sectors, providing in-depth reporting on the connectivity lifelines of the nation. Expertise & Focus Areas: Mishra’s journalism is focused on two of the country's most capital-intensive and public-facing ministries: Ministry of Railways: Tracking the operations, safety, and development of India's vast railway network. Ministry of Road Transport & Highways: Covering policy decisions, infrastructure projects, and highway development. What sets Mishra apart is his rigorous use of the Right to Information (RTI) Actas a primary tool for news gathering. By relying on official data and government records, he ensures a high degree of accuracy and trustworthiness in his reporting. This data-driven approach has resulted in numerous impactful reports that hold public institutions accountable and bring transparency to government operations. Find all stories by Dheeraj Mishra here ... Read MoreStay updated with the latest - Click here to follow us on InstagramTags:Ahmedabad-Mumbai bullet trainbullet train India