Monitoring for Hong Kong Airport Authority Contract 3205 | China

650 hectares reclamation near existing airport

The Third Runway System of Hong Kong International Airport is a project to build a new runway on 650 hectares of reclaimed land north of the existing airport island. Contract 3205 will carry out soil improvement works by low headroom Deep Cement Mixing (DCM). During the reclamation process, the monitoring of the seabed settlement and movement is important for the reclamation progress review, therefore a series of instruments were designed to carry out this monitoring.

The monitoring system included subsea instrumentation in three different areas. At each area, a DCM column was selected for installation of a vertical shape array to measure the lateral movement along the column. Another shape array was installed with piezometer sensors in the seabed for lateral movement, as well as pore water pressure monitoring in the different stratas. For settlement monitoring, a 25-35m horizontal shape array was laid on the seabed. In addition, earth pressure cells were used for measurement of the loading from reclamation.

Challenging installation procedures

All the sensors were installed underwater, installation works were done from a jack-up barge with the assistant of divers. The challenge was to protect the signal cables from damaged and water ingress. Steel channels were used as cable tray on the seabed. All cable connections were protected by submersible cable splicing kits and cabled to Dataloggers.
The Dataloggers were housed in stainless steel, weather proof enclosures and installed on top of a pile above high water levels. The dataloggers are solar powered. Measurements was done automatically with data transferred in real-time to our Geoscope database. Therefore manual attendance is minimal throughout the monitoring.