The Asian Development Bank is working with the Philippines to modernize Manila's water supply and reduce the risk of water shortages as demand rises in tandem with the city's booming population.
An ADB funded project is using modern tunnel boring technology to excavate a fourth supply tunnel for the La Mesa reservoir, a major source of water for Metro Manila. The technology is faster, cheaper, and safer than the traditional drill and blast method. Once the tunnel is complete, rehabilitation works will begin on existing supply tunnels, ensuring continuous water supply.
Norzagaray, Philippines - The La Mesa reservoir is a critical source of water for Metro Manila and its 12 million plus population.
Three tunnels supply water to the reservoir, but they are old and in need of repair.
A new project is building a fourth tunnel.
When it becomes operational in 2019, work on rehabilitating the other tunnels will begin.
The project is using a 240-meter long tunnel boring machine which is safer and faster than the traditional ‘drill and blast’ method.
“50 years ago, the main way to excavate a tunnel was using drill and blast. That is a very ancient method. One century ago more or less. And using drill and blast, you’re not protected by shields like this TBM or lining. You first drill holes, you charge the holes with explosives and you make a big boom. So this is disturbing a lot of rocks,” contractor Salvatore Lavalle of the Angat Dam Water Transmission Improvement Project says.
Use of the tunnel boring machine is expected to reduce construction time by one year.
“This tunnel boring machine functions like a drill. It’s just like a big drill getting to the mountains, to excavate, to create what we call the tunnel. So practically what it does is, the cutter head rotates and during rotation, it breaks the rock component and after that, we install these segments," Principal Engineer Jose Dorado, Jr. of the Metropolitan Waterworks and Sewerage System says.
After installation of the segment lining, it pushes forward. So while it excavates, simultaneously the segment lining is installed.
MWSS Administrator General Reynaldo Velasco adds: “This kind of system, the walls are already put in place immediately, so these are the walls that hopefully, under our standards, should meet 8.0 earthquake.”
Every day, rocks are probed for suitability before excavation begins.
“We detect how is the rock ahead, to adjust the parameters of the excavation in order to suit the type of rock that is going to excavate for that day,” Salvatore Lavalle says.
In a constant cycle, an empty train goes inside the tunnel carrying construction materials.
The train then comes out of the tunnel with the gravel, which is recycled to build roads.
Funded by the Asian Development Bank, the work will guarantee water supply to Metro Manila for years to come.