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Thermwood

Trenchless Technology used in Water Main Rehabilitation

28 August 2009

Using composite materials, Black & Veatch has completed the rehabilitation of the first of five water mains that lie beneath the heavily trafficked Lion Rock Tunnel in Hong Kong Special Administrative Region.

Black & Veatch adopted the use of hand-applied fibre reinforced plastic (FRP) for the repair of the mains, completing the first main by mid-December 2008 at an average rate of approximately 25-40 metres per day.

They used a lightweight, high-strength FRP system which was applied as sheets of resin impregnated glass fibre to the pipe wall. Black & Veatch used two layers of glass fibre fabric, which was used to build up a laminate in order to achieve design strength and limit the loss of cross-section area within the pipe.

The lining process involved the application of an initial tack coat of epoxy to enhance the bond between the host pipe and FRP lining.

Following that, the glass fibre fabric was then soaked with resin and placed on the pipe wall. Once placed, top coat resin was then applied.

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, 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 kilometres in length and range from 1.2 metres to 1.5 metres in diameter.

Discussing access issues, Alan Man, Vice President of Black & Veatch said, “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. Major excavation of the carriageway was not allowed and replacement was not possible.”

“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,” Man added.

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 in 2000, said to be one of the largest pipeline rehabilitation programmes in the world. The programme 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 programme, and is involved in Stages 1, 2 and 4.