Mumbai, India – A significant engineering setback has left a German-made Tunnel Boring Machine (TBM) entombed nearly 60 meters beneath the bustling streets of Powai, Mumbai. The colossal machine, deployed by the Brihanmumbai Municipal Corporation (BMC) for a critical water conveyance tunnel project, has been abandoned since 2019 after becoming trapped in unstable pyroclastic ash.
A Complex Project Faces Unforeseen Challenges
The ambitious project, initiated in 2012, aimed to construct a 6.6-kilometer water tunnel from Veravali to Ghatkopar. The TBM, manufactured by Herrenknecht, was tasked with excavating a 4.4-kilometer stretch from Powai towards Ghatkopar. However, after boring approximately 1.2 kilometers, the machine encountered an unprecedented engineering challenge when it became lodged in highly loose and unstable volcanic ash. This rare geological condition brought the excavation to a complete halt, leaving the German-made TBM stranded over 3 kilometers short of its destination.
The Brihanmumbai Municipal Corporation, despite its extensive experience in executing water tunnels, faced an unprecedented setback. Repeated attempts to retrieve the trapped machine proved futile, and by 2020, heavy monsoon flooding rendered extraction virtually impossible. Consequently, the BMC made the difficult decision to abandon the original tunnel and the TBM, writing off the significant investment.
A New Approach for Project Completion
In December 2022, a fresh tender was floated to complete the remaining stretch from the Shipping Corporation of India (SCI) establishment in Powai to Ghatkopar. Patel Engineering was awarded the contract for Rs 419 crore, with stricter conditions incorporated into the tender. Recognizing the persistent challenges posed by the loose soil conditions, the BMC opted for a different approach for a portion of the remaining excavation. Instead of relying solely on a TBM, the New Austrian Tunnelling Method (NATM) was employed for nearly 420 meters of the stretch. This method involves manual excavation with continuous support systems, such as rock bolting and steel liners, to stabilize the ground.
Despite these challenges and a decade-long project timeline, the new TBM achieved its breakthrough in August 2025. Abhijit Bangar, Additional Municipal Commissioner Projects, stated that the work is nearing completion, with boring and NATM excavation finished. The lining work is progressing, and the project is expected to be completed by March 2027. However, no viable solution or proposal has been charted for the retrieval of the original, abandoned TBM.
Broader Context of Mumbai’s Underground Infrastructure
This incident highlights the complexities and inherent risks associated with large-scale underground infrastructure projects, particularly in geologically challenging urban environments. Mumbai, a city constantly striving to expand its infrastructure to meet the needs of its burgeoning population, has seen a surge in tunneling projects for its Metro lines, road networks, and water supply systems. The Mumbai-Ahmedabad Bullet Train project, for instance, is also employing advanced Tunnel Boring Machines for its extensive underground and undersea tunnel sections, underscoring the growing reliance on this technology for major civil engineering endeavors in India.
The Bullet Train project’s underground segment, spanning 21 kilometers between Bandra Kurla Complex (BKC) and Shilphata, will utilize TBMs for the majority of its length, with 16 kilometers to be excavated by these machines. The project also notably includes India’s first 7-kilometer-long undersea rail tunnel beneath Thane Creek. The assembly of two massive TBMs, each weighing over 3,000 tonnes and supplied by German manufacturer Herrenknecht, has commenced at Vikhroli and Sawli. These machines, utilizing Mix Shield/Slurry technology, are designed for complex geological conditions, with excavation expected to begin in July 2026.
The Powai TBM incident serves as a stark reminder of the unforgiving nature of subterranean construction. While technology has advanced significantly, as seen with the current Bullet Train project, unforeseen geological conditions can still pose substantial obstacles. The incident also raises questions about risk assessment, contingency planning, and the long-term management of such colossal machinery when projects encounter insurmountable difficulties. The fate of the abandoned TBM beneath Powai remains a testament to the formidable challenges inherent in reshaping the urban landscape from below.
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The Chenab Times News Desk
