HCC’s Maroshi-Ruparel water tunnel project
Mumbai’s water network is crumbling under the strain. Its mains system is at least 80 years old, the majority of it laid in the colonial era. Though the city has seen some water distribution projects post-independence, these are still more than 60 years old.
Much of the system works through surface pipelines, which are prone to leakages and theft. This highly pressurised network is further hindered by passage under slumland, which adds even more complication to their maintenance. Likewise, Mumbai’s main water line runs beneath the runway of Mumbai international airport, making it doubly difficult to maintain, while a major burst could affect the movement of air traffic into and out of the city.
With the population of Mumbai now officially at 20 million, although likely significantly more, the city’s municipality, the BMC, has been forced to take urgent measures to upgrade the water network.
A number of water projects have been implemented over recent years, including three new tunnels that stretch from Ruparel College to Malabar Hill reservoir via Mahalaxmi Racecourse in the south-west of the city, from Mulund to Kandivali in the north and from central Matunga to Sewri.
Ongoing work, which began in 2007, includes three tunnels to replace the old pipeline. These comprise a 3.6-km tunnel, now almost 80 per cent complete, from Malabar Hill to Cross Maidan in the south-west of the city; a 6.1-km tunnel from Verawali to Yari Road in the northern suburbs, partially commissioned earlier this year; and from Maroshi to the north of the city to central district of Ruparel, a 12.24-km tunnel is now 70 per cent complete and expected to be finished by September, 2013.
Last month, Construction Week visited this latter project to gain an understanding of how one of the longest tunnels in the city has been progressing in spite of space and infrastructure pressures, and find out the current status of the project, which is being executed by the Hindustan Construction Company (HCC).
The Maroshi-Ruparel tunnel will replace the existing Vaitarana, Tansa East and Tansa West main surface pipelines, which are now almost a century old or even more. In all, the project will cost Rs480 crore.
As a means to supply uninterrupted water to the western suburbs and south-western districts of Mumbai, the tunnel, measuring 3 metres in diameter, has been divided into three stretches: Maroshi to Vakola, Vakola to Mahim and Mahim to Ruparel.
The project also involves constructing three, 10-metre wide shafts at Mahim, Vakola and Maroshi besides the existing shaft at Ruparal. Each one is up to 80 metres deep — equivalent to a to 26-storey building deep into the ground.
The Vakola-Mahim section passes below the Mahim creek while the Maroshi-Vakola section crosses both of Mumbai airport’s runways at around 70 metres below ground level.
BMC town planners expect the new tunnel to have a number of advantages over the existing surface pipeline, not least because it travels at such great depth, meaning that the structure cannot be tampered with, as is the case with surface pipelines. In addition, there are fewer chances of leakages and water theft, and most importantly, the tunnel is not expected to require major maintenance over the next 100 years. And since the entire distribution system is made of concrete, it will not corrode, invariably happens with surface pipelines.
First, a shaft with a diameter of 10 metres was constructed at a depth of between 70 and 80 metres. This served so that contractors could deliver all the necessary plant, machinery and equipment, including tunnel boring machines (TBMs), locomotives, water pumps and concrete mixers, through it to reach the 70-metre depth required for the boring and drilling.
Once in place, work began on boring the network. This was done by the gripping of jacks and alignment of TBM cutter heads for boring at a width of 3.6 metres through the earth. Locomotives would be used to transport the detritus into mine cars, which would pass from bottom hopper to skip before being lifted to the shaft-top by winch. This material would be unloaded and taken to a stockpile on conveyor belts before the skip is brought down once again using a winch and sent back to the TBM on a mine car.
The concrete lining is cast on site rather than being pre-cast elsewhere. Once a stretch of boring is complete, an epoxy-coated reinforcement layer is fixed into place; the shutters and bulkheads are then set to pour ready-mix concrete using the agitator cars. When the concrete is hard , the rail track is removed and repositioned down the line for the next pouring.
The project began in December 2007 with a completion timeline of 56 months. With almost 70 per cent of the project already finished, the Maroshi-Ruparel tunnel is expected to go into service by the end of September, 2013.
The current status of all the three starches is:
• Maroshi-Vakoka (5.83 km)—Completed
• Vakola-Mahim (4.55 km)—Boring complete, concrete lining in progress
• Mahim-Ruparel (1.86 km)—Boring in progress, concrete lining to be done
With funding from the Government of India, the Maharashtra government and the BMC, as part of the Jawaharlal Nehru National Urban Renewal Mission for urban renewal, the project is part of the wider rehabilitation and improvement of the drinking water movement and distribution from Bhandup Treatment Works through the western suburbs and to the south-west section of the city. HCC has constructed 21 km of the existing 26 km of water tunnels that supply drinking water to Mumbai, and is in the process of constructing a further 12 km within the 23 km of water tunnels that are currently in progress. The 12-km long Bhandup Complex to Charkop tunnel was the most recent tunnel completed by the company.
Although it is hoped that the Maroshi-Ruparel tunnel will improve water distribution within the city, it is a rehabilitation project and not an expansion of the existing network. With the growing population in Mumbai, the city needs more new projects to meet future demand. After much delay, Mumbai’s ambitious Middle Vaitarna dam project is expected to be completed by May 2012, and this Rs1,400-crore project should supply an additional 455 million litres of water per day to the city. This will help to reduce water shortage problems in the future.
Interview with Nirmalya Deb, deputy project manager, Maroshi-Ruparel tunnel project
Did you take extra precautions for the sections going through Mahim creek and Mumbai airport?
Initially, we were very concerned about the geological conditions under Mahim creek. And also we thought that there we might cause vibrations as we passed under the Mumbai airport runway area. Luckily, we didn’t face any such problems since the geological conditions were alright. As a result, we didn’t need to take any extra measures.
What environmental protection measures have you taken?
The basic environmental coverage was taken by BMC itself. They secured all the necessary environmental clearances from various departments so we didn’t have to go through this lengthy process. We have implemented all environment protection measures that are required by our internal integrated management systems. This involves wastage control and hazardous waste handling, among others.
What is the longevity of the tunnel?
The tunnel is designed to last 100 years. It does not require any repairing in normal circumstances — in fact, you can’t perform any repairs. However, if an incident occurs, we will be forced to close down that location, complete the repairs and come back. The project is also designed to withstand earthquakes.