Cofferdam excavation using soil nail tie-backs for Ocean Park funicular tunnel portal

摘要

This paper describes the cofferdam excavation for a tunnel portal to facilitate construction of a new funicular tunnel as part of the redevelopment of Ocean Park. The portal wall was supported by pipe pile wall with soil nail tie-backs instead of ground anchors proposed by the reference design. As the design was jointly developed with the Contractor, it is able to address a number of constructability issues to suit the Contractor’s particular method of construction. Construction of the tunnel portal was particularly challenging as it involved working within very restricted land boundaries and works were carried out as the theme park remained open to visitors. Various instrumentation and monitoring works were carried out to ensure safety of the works and public. The final part of the paper compares the measured settlement against the design predictions, following completion of the excavation and temporary support works. The revised design was able to provide substantial savings, both in terms of construction time and cost, as the original reference design using ground anchors would have required a longer installation time and a more comprehensive set of performance tests.