Tunnel wall assembled by precast segments

The MTR Corporation recognizes safety is of paramount importance. During the planning and design stages of the Express Rail Link Project (XRL), the Corporation has duly conducted comprehensive assessments on the area in the vicinity of the alignment. Geologic survey of the site areas and in the vicinity of the alignment, and condition survey of the structures nearby, etc. have been conduced. The detailed design and the construction methods are carefully reviewed and chosen based on the assessment results with a view that the nearby structural integrity and the ecological environment will not be affected. Moreover, monitoring points and condition surveys will be arranged as appropriate along the alignment in order to further ensure the safety of the project, easing concern of the public members.

Tunnel boring machine (TBM) tunneling is effective and commonly used method in today’s tunnel construction around the world. Risk of settlement will be greatly reduced and loss or movement of the underground water table will be avoided, significantly minimizing the impact on the community and environment. The Environmental Impact Assessment Report and other relevant assessment studies reveal that the alignment of the XRL tunnels will have no adverse impacts on the underground water level and structural integrity of the areas nearby during both construction and operation stages.

Tunnel boring method is widely and commonly used in Hong Kong and worldwide, with examples of the Channel Tunnel in Europe, the Lok Ma Chau Tunnel of the East Rail Line and the Tai Lam Tunnels of the West Rail Line in Hong Kong. To facilitate the construction works of the XRL Project, TBM tunneling will be adopted in the sections along Yau Tsim Mong, Sham Shui Po and Yuen Long districts. This tunneling method is effective to avoid loss of underground water, minimize settlement and the impact to the environment and the neighboring communities. During tunnel construction, the excavated face will be supported by the shield near the front of the TBMs while permanent precast segmental tunnel linings (walls) will be installed immediately behind the cutterhead of the TBM. Any voids between the excavated wall and the linings will be filled with cement grout. This will ensure the excavated surface is always supported and the impermeable tunnel walls will not lead to loss of ground and underground water.

The MTR Corporation is experienced in building and operating tunnels in densely populated and environmentally sensitive areas.

Precast tunnel segment is fixed immediately after the excavation drilling with TBM to make a permanent tunnel wall. This arrangement is effective in reducing the risk of settlement, any loss or movement of underground water table.

Tai Kok Tsui – Ground Investigation along the Alignment of XRL

During the design stage of the XRL tunnels, the Corporation has adopted the existing effective and professional procedures for tunnel design, including conducting surveys on the geology of the tunnels and nearby area, as well as comprehensive reviews on relevant drawings and records, in order to obtain a complete set of detailed geotechnical data along the alignment.

Along the section of XRL tunnels from Tai Kok Tsui to Hoi Wang Road in Yau Tsim Mong district, most part of the XRL tunnels will be constructed about 30m underground, which is far deeper than the foundation of the buildings in the vicinity. The geotechnical investigation report sees fill materials or alluvium at upper level (soil strength relative to soft or silty) and completely decomposed granite at lower level in this area, which is a common geology found in the reclaimed area and all over the territory in Hong Kong. Major skyscrapers, flyovers and tunnels are being constructed on lands with similar geology in Hong Kong.

Similar to Tai Kok Tsui is the Kowloon Southern Link – the tunnel boring machine passed through the foundation of the flyover near to Kowloon Park Drive and former Marine Police Headquarters whereas the tunnel was constructed about 5-6m from the ground. The flyover and the former Marine Police Headquarters were not affected by the tunnel construction. During the operation stage, there is no impact to the hotels and the Cultural Centre nearby to the alignment.

Most of the XRL tunnels will pass through the rock level in Tai Kok Tsui and with much distance between the tunnels and the foundation of the buildings. The tunnel construction and operation will not affect the structural integrity of the buildings nearby.

Ngau Tam Mei – Underground Water Will Not Be Affected by Tunnel Works

The section of XRL tunnels from Mai Po to Ngau Tam Mei will also be constructed by TBMs. The distance between tunnel top and ground surface will be around 20 to 70 metre. Building the tunnels at Long Valley of the Lok Ma Chau Spur Line would be similar to the situation in Ngau Tam Mei. The tunnels in Long Valley is at least 8 metre below the ground level where the tunneling method did not have any impact to the underground water nor to the ecological on the surface.

The tunnels at the Ngau Tam Mei section are not expected to have any impact on the underground water level and will not affect the wells and fish ponds in the vicinity of the alignment of the XRL project. The Environmental Impact Assessment Report also indicates that the construction of the Express Rail Link, including the works of tunnels and ventilation facilities, will not have adverse impact on the underground water in Ngau Tam Mei. Nevertheless, monitoring points have been set up along the alignment, including at nine wells in the Ngau Tam Mei area which would provide a representative picture of the overall situation of underground water in Ngau Tam Mei to reassure the public that the only noticeable effect is minimal or negligible. The location of monitoring points has been in due consideration by the Corporation, consultants and relevant government departments.

The drilling Jumbo, on its arrival at the Shek Yam work sites in Tsuen Wan from Sweden on 6 July 2010 for the construction of Contract 822 of the Express Rail Link.

"Jumbo" is not only an adjective for size, but also a new heavyweight member of the construction team for the Express Rail Link (XRL) project.

The Swedish-made DT820-AC "Jumbo", weighing 27 tonnes, is a powerful two boom electro-hydraulic drilling rig for rock tunnelling. On 6 July 2010, "Jumbo" arrived at the Shek Yam construction site in Cheung Wing Road, Tsuen Wan for the construction of part of the XRL's 26km of tunnels.

For tunnel drill and blast operations, the multi-boom "Jumbo" equipped with computerized and pre-programmable facilities will be utilized for blast hole drilling on the rock face. Once the blast hole drilling is complete, blast holes will be charged with explosives and the explosives will be detonated by shotfirers.

"With appropriate safety measures controlling the blasting works, the Corporation and the contractors are confident that the daily activities of the public will not be affected," said Project Manager – XRL Tunnels Mr Alan H. Morris.

Five more drill and blast rigs from various suppliers (notably, France and Finland) will arrive in Hong Kong by the end of 2010 and mid-2011 respectively for the construction of the rock tunnel sections of the XRL – Contracts 821, 822 and 824.