Green light at the tunnel's END

Green light at the tunnel's END

Tunnelling is a better solution to traffic problem than road-widening: Experts

Team DNA. Bangalore



BBMP's ambitious road-widening work may ride over many a dream home. There is resentment, anguish and resignation among the public over the instrument that is being deployed by the administration for wider roads. The concept of TDR (transfer of developmental rights) is new and an uncharted territory for Bangaloreans.
As people come out strongly against TDR, experts suggest alternatives that can help ease the problem of choked roads but, at the same time, cause the least amount of trouble to residents
Tunnelling, using the innovative TBM (Tunnel boring machine) technology, can be a good option, says SVS Subramanya Gupta, director, Advaith Hyundai. It will not only spare residents who now stand to lose their life's investment, but also create a first-of-its-kind solution to accommodate the ever-increasing population of both public and private vehicles on city's roads.
Sachindra Bhat, group general manager of SNC Power Corporation Private Limited, who is a qualified structural engineer, says TBM can be quite effective. "With TBM, the entire work is done underground; it is a silent process," he says. The work will be done 15 to 20 metres below the ground.
But, given the city's topography, will it not be a difficult task? "There is no explosives material used, instead it is a rotary crushing system," Bhat says. "The strata that are crushed will form slurry as we would use some adhesive and water. A conveyor system will then be used to clear out the slurry."
The technology also facilitates a continuous process. As the machine crushes and excavates the ground, a segment erector will instal the pre-cast RCC (reinforced concrete and cement) segment into the tunnel. Hence, explains Bhat, there will be no "shaking ground" above. The machine is equipped with a shield that can protect about 12 metres of the unprotected tunnel.
All this sounds great, but the process could be time-consuming and a costly affair. "The machine can excavate 10 metres to 15 meters per day," Bhat says. "Taking a minimum of 10 metres per day, in a month, the machine can excavate 300 meters. A stretch of 1.5 km can be tunnelled in 5 months," he says.
That's the time required only for the actual work. Before that the machine has to be imported. Two months will be needed to erect and commission it. That means, it will take about seven months to make a tunnel 1.5 km long, Bhat points out. But it will be worth it since it will save the city more chaotic traffic diversion.
Bhat says that the city needs two such tunnels to carry traffic back and forth between Jayanagar and Maharani college. "Traffic from the city market and Maharani College is two-way; only at Avenue Road is it one way. The two-way tunnel can work wonders by ensuring easy and quick connectivity," he says.
Another point to ponder is the cost of such a project. The machine alone may cost Rs75 crore since it has to be imported, Bhat says. Then accessories like ventilation, electrical and conveyor system and other mandatory installations may cost up to Rs110 crore. The RCC lining could cost another Rs25 crore. If the operational and maintenance cost is also to be considered, then Rs140 crore to Rs150 crore will be needed as investment for every kilometre of tunnelling, he says.
On the flip side, land will have to be acquired only at the entry and exit points of the tunnels. "Unlike in the surface method, where, to broaden a road, land on both sides has to be acquired, here only the entry and exit points will need extra land." Bhat dismisses concerns about ventilation and lighting in tunnels. A stretch of 1.5 km is manageable, he says. Such a stretch should ideally be tunnelled with the drill-and-blast method, but "since the ground condition is quite difficult, the TMB method is a safe and it ensures quality".
Maintenance of tunnel, says Bhat, will be required. "But, the cost, when compared to exposed roads, will be minimal."the way ahead: Road widening can affect normal life, but tunnelling will cause only minimal disruptions, say experts