Interception is an innovative flood prevention scheme at urban area. A drainage tunnel is constructed at the upstream which provided an invisible shelter to intercept the rain water from the hinterland at the mid-level. Rain water bypasses the crowded urban area at downstream and directly discharge to the habour.
Tunnel Boring Machine “One machine two usages”
Since “branch tunnel” is located at rock stratum while “main tunnel” is located at reclamation area, traditionally these two sections of tunnel require two tunnel boring machines with different designs for the drilling works. Considering building a tunnel boring requires a lot of resources, the innovative project team designed the first and ever “All Around” tunnel boring machine “Dae Janggeum” in Hong Kong. With its special design, it successfully completed the branch tunnel consisted of hard rock and main tunnel consisted of soft ground with high pressure technique. At construction stage, although it was only a few feet away from the surrounding foundations and underground railways, it still achieved “zero disturbances” to all the adjacent facilities and be completed on time. It saved HK$100M cost in the tunnel boring machine and the resources for building an extra tunnel boring machine. It successfully bored two sections of tunnel with different geological stratum with a solution which fulfills sustainable development policy.
Constructing Tunnel under High Pressure
The main tunnel is located 45m below ground of an urban reclamation area, the geology is mainly mix-ground and soft ground. To ensure the construction not affecting the surrounding facilities and foundations, the front of the tunnel boring machine is required to be pressurized to prevent the loss of underground water and soil. The cutter heads of the tunnel boring machines require regular replacement and maintenance, and the technicians were required to work under 4.2 times atmospheric pressure. This is the first time ever in Hong Kong applying such a high atmospheric pressure in a tunnel construction project. Project team employed an overseas medical expert and established detailed working procedures. The construction process and staff’s health conditions were strictly monitored to ensure construction safety.
55 numbers of high pressure operators were employed for this project. After hundred times of compressed air working procedures, there was no decompression sickness happened. This record is better than other high pressure tunnel construction overseas. This project introduced a new high pressure tunnel construction technique to Hong Kong tunnel construction industry and laid a solid technical foundation for those in the future.
The main tunnel is required to pass through an area crowded with foundations of 4 operating railways and foundations of a number of viaducts within a short distance.