An Innovative ELS System on Recently Reclaimed Land – Design and Analysis

The Third Runway at Hong Kong International Airport sits on a newly reclaimed land formed by non-dredged method where soft muds remain in place under the reclamation fill. Ground improvement works mainly in the form of Deep Cement Mixing (DCM) were installed within the soft marine clays with embedment into a competent stratum. The APM and BHS tunnels were proposed along the new artificial shoreline. To enable the construction of the cut-and-cover tunnels, it is viable to have an open-cut excavation at landside because of the abundant space. At seaside where space constraints are present, a double-wall system was introduced to retain the earth. The beauty of this system is a strut-free zone can be created, which minimizes the construction constraints and shortens the construction programme significantly. A double-wall system is composed of continuous front wall and discrete back wall connected by steel ties. The front wall relies on the back wall which is anchored into DCM panels. The spacing between the front wall and the back wall varies from 9m to 15m depending on site constraints. The design approach and failure mechanisms are discussed.