The water margin

Hong Kong's new rail line to the Chinese border is being built across environmentally sensitive wetlands. The 7.4km route between Sheung Shui and Lok Ma Chau crosses the Long Valley area of the Mai Po wetlands, home to 60,000 migratory birds. Following pressure from green groups, the line is to be built underground beneath the wetlands. The project will consist of four sections: modernisation of the existing Sheung Shui station, the Sheung Shui to Chau Tau twin tunnels, a western viaduct and Lok Ma Chau station. A footbridge will link the station to China across the Shenzhen river. The tunnels have been driven using an earth pressure balance tunnel boring machine for 3. km under the Long Valley. Cut and cover construction has been used for the 700m of tunnel adjacent to the viaduct. Kowloon-Canton Railway Corporation has reclaimed land to extend the wetlands area to compensate for land lost to the new Lok Ma Chau station. Due to environmental constraints a full site investigation of the Long Valley area was not possible. The engineering team relied on old borehole logs and geological maps, which revealed decomposed volcanic soil with hard rock above and soft ground below. Stringent thresholds were imposed on settlement during construction. Ground freezing was used in the construction of cross passages between the two tunnels in waterlogged ground.