By Vishal Jambhale, Chief Engineer, Mumbai Metropolitan Region Development Authority
The expansion of underground infrastructure is a significant step in Mumbai’s efforts to enhance road connectivity. High vehicle density, narrow roads and saturation of the existing surface network have increased the need for tunnel-based infrastructure solutions. Several key road tunnel projects are being planned and executed under the guidance of Dr. Sanjay Mukherjee, Metropolitan Commissioner, Mumbai Metropolitan Region Development Authority (MMRDA). Currently, two flagship projects are under execution – the Thane-Borivali twin tunnel project and the Orange Gate-Marine Drive tunnel project.
Thane-Borivali twin tunnel
The Thane-Borivali twin tunnel, spanning a length of approximately 11.85 km, is expected to bridge the missing direct east-west link beneath the Sanjay Gandhi National Park. Being developed at a cost of around Rs 188 billion, the twin-tube tunnel will have an outer diameter of 12.89 metres. The project involves the use of four Herrenknecht hard-rock shield tunnel boring machines (TBMs). Tunnelling progress has been faster than expected owing to the presence of hard rock ballast, with daily excavation advancing by around 10-11 metres. Once completed, the tunnel is expected to reduce travel time by 40-45 minutes. A major challenge was the tunnel alignment passing beneath the Sanjay Gandhi National Park. Given the on-ground sensitiveness, the forest department did not permit the construction of even a single ventilation shaft within the area.
Orange Gate-Marine Drive tunnel
The Orange Gate-Marine Drive tunnel bypasses the dense South Mumbai chokepoints under heritage and transit assets. With a length of 5.9 km, the project is being developed at a cost of Rs 77.56 billion. The twin-tube tunnel has an outer diameter of 11.75 metres and is being excavated using two CRCHI slurry-face shield TBMs, which are suited to the water-bearing mixed ground conditions. The daily excavation progress stands at 6-8 metres. The project achieved a notable milestone with the launch of the first TBM in a record time of 18 months in December 2025. The initial drive was completed in January 2026, and around 450 metres of tunnelling has been achieved so far. The south bound tunnel is expected to reach Marine Drive by December 2027, and the entire project is slated to be completed by December 2028. The tunnel is expected to facilitate an 85 per cent reduction in travel time, from 30-35 minutes via the existing route to just four to five minutes.
Best practices shaping construction
A fully mechanised boring technique was used for both projects, featuring state-of-the-art TBMs. Both the drill-and-blast and the New Austrian Tunnelling Method were ruled out in order to prevent vibrations from causing disturbances to wildlife in the eco-sensitive zone and to avert any possible risks to sensitive urban structures.
An AAA (alert, action and alarm) distress management protocol has been adopted for project monitoring and real-time response. In the past, building damage claims have been reported as a result of tunnelling activities. The Orange Gate-Marine Drive tunnel, in particular, passes under the dense South Mumbai area, with heritage buildings. To prevent such issues post construction, a multilayer mechanism was adopted. A building condition survey (BCS), featuring a three-tier instrumentation with tilt meters and optical targets on buildings, D-wall inclinometers, piezometers, stand-pipes, etc., was undertaken to ensure controlled excavation with minimum on-ground vibrations.
The MMDRA has also implemented an automated concrete distribution system, facilitating the complete automation of segment casting, relocating, supplying and fixing, while tracking segment production, stacking, despatching and erection. The MMDRA has also deployed the tunnel segment management system (TSMS) for effective monitoring of tunnel construction processes. It facilitates end-to-end tracking of segment production, stacking despatch to sites and erection. These elements, along with other stages like moulding, concreting and demoulding, are also digitally recorded and tracked through barcode labels and mobile scanners.
Upcoming opportunities
The “Mumbai in Minutes” is a key upcoming project aimed at reducing travel time to within 59 minutes via any mode of commute. Some of the key projects undertaken by the MMRDA under this initiative are the Gaimukh to Fountain Hotel twin tunnel project, and Mumbai Metro Lines 5 (Phase II), 13 and 14, which are under the pre-tendering stage. Moreover, a 70 km integrated tunnel master plan is proposed to be developed in three phases based on future traffic demand patterns and requirements. The feasibility study for the first phase is expected to be completed soon, followed by which the detailed project report will be prepared.
In sum
The adoption of state-of-the-art tunnel boring technologies is essential in Mumbai’s ecological and urban environment to help address gridlocks, protect heritage structures and accelerate transit. As seen, the adoption of such advanced practices has had a positive impact on the surrounding infrastructure. Notably, both projects have avoided the displacement of any township, preserved ecologically sensitive zones, and safeguarded historical structures and key transit assets in the South Mumbai region.
