ABSTRACT
Route 3 is a strategic expressway across the north-west New Territories of the Hong Kong Special Administrative Region (SAR) which was procured as a fast-track design and construct project. The Country Park Section north of Tai Lam Tunnel included extensive embankment formation over land occupied by large fish ponds and underlain by soft alluvial soils.
Major geotechnical risk factors that had to be addressed included the stability and performance of these embankments. At an early stage it was recognised that the settlement of the foundation soils could be considerable and of a highly variable rate, with the stability during construction of the high embankments also being a concern. Another key factor was how to establish an appropriate point when pavement construction could commence, with the confidence that long-term settlements would be within acceptable limits. Design solutions based on a risk-management strategy were established, with it being determined that ground improvement, staged construction and surcharging were appropriate to best address the geotechnical risks.
In response to the challenging construction programme, and recognising that the performance of the foundation soils might be better than predicted, it was also decided to adopt an “Observational Approach” to the earthworks construction. A series of performance criteria were established so that decisions and appropriate actions could rapidly be taken during construction and extensive instrumentation was therefore installed to control the works. Early agreement on the construction control criteria, responsibilities, and contingency measures between the Designer, Contractor and Project Manager, was a critical success factor for this fast-track project.
This paper concentrates on the measured performance of the embankments during construction, specifically the pause periods that were required during staged construction, the response to surcharge loading and the trend of long term creep settlements.
Particular benefits that accrued from the geotechnical approaches adopted in the project included significant shortening of the pause periods during and after construction of the embankments compared to the periods envisaged at design stage, as well as the earliest completion of pavement construction.
