“One of the major constraints on this project was getting access to the mains,” said Alan Man, Black & Veatch Vice President and leader of the company’s water business in Hong Kong SAR. “Access to the pipe gallery via the shafts within the tunnel is permitted for only 14 days a month and then only between 1:30 am and 6:00 am.”
The Lion Rock Tunnel is a vital component of Route 1 that connects Sha Tin in the New Territories and Kowloon. The five water mains that lie beneath the carriageway of the Lion Rock tunnel transfer treated water from the Shatin Water Treatment Works, the largest water treatment facility in Hong Kong, to the heavily populated areas of Kowloon and Hong Kong Island. The mains, which were built in the 1960s and ‘70s, are approximately 1.4 kilometers (km) in length and range from 1.2 meters to 1.5 meters in diameter.
“Major excavation of the carriageway was not allowed and replacement was not possible,” said Man. “As conventional rehabilitation techniques such as slip lining were also not feasible, we had to use innovative in-situ methods within the pipe to get the job done.”
Black & Veatch adopted the use of hand-applied fiber-reinforced plastic (FRP) for the rehabilitation of the mains. Various trials and demonstrations on the FRP system were carried out on site. Relining of the first main was completed by mid-December 2008 at an average rate of approximately 25-40 meters per day. Final inspections and pressure tests were completed and the first water main was re-commissioned in March 2009.
Work has now commenced on two other mains with all five mains targeted to be completed in early 2011.
“The Lion Rock Tunnel water mains are an essential component of Hong Kong’s water supply network,” said Man. “By using innovative technology, we are able to successfully rehabilitate these mains with minimal disruption to commuters who rely on the use of the tunnel every day.”
Hong Kong’s Water Supplies Department launched the Replacement and Rehabilitation Programme of Water Mains, one of the largest pipeline rehabilitation programs in the world, in 2000. The program aims to rehabilitate or replace a total of 3,000km of water mains by 2015, at an estimated cost of HK$ 19.2 billion (US$ 2.5 billion), improving the condition and reliability of Hong Kong’s water supply network.
Black & Veatch is responsible for replacing or rehabilitating approximately one-third of the pipelines in the overall program, and is involved in Stages 1, 2 and 4.
- FRP is a lightweight, high-strength system which can be applied as sheets of resin impregnated glass fiber to the pipe wall.
- In this particular case, two layers of glass fiber fabric were used to build up a laminate to meet the design strength with very little loss of cross-sectional area in the pipe.
- The lining process involves first applying an initial tack coat of epoxy to enhance the bond between the host pipe and FRP lining.
- The glass fiber fabric is then soaked with resin and placed on the pipe wall; the final stage involves the application of a top coat of resin.