PERFORMANCE OF A ROAD EMBANKMENT ON SOFT CLAY SUPPORTED ON A GEOCELL MATTRESS FOUNDATION

A five kilometre-long road was constructed in the New Territories of Hong Kong between 1989 and 1992. Part of the road crossed an alluvial plain on an embankment, and at two locations on the alluvial plain this embankment was underlain by soft clay deposits. A geocell mattress was used as the means of supporting the embankment on these soft clay deposits. Wick drains were installed beneath the embankment to speed up consolidation of the soft clays, and using staged construction the embankment was built up to a maximum height of 10 m. The embankment was fully instrumented with pneumatic piezometers, inclinometers, hydrostatic profile gauges, settlement plates, surface settlement markers, and lateral movement blocks. This paper presents the results of the instrumentation monitoring and the performance of the geocell mattress foundation during the construction of the embankment. At one section, unusually high excess pore water pressures and a slight heave of the toes of the embankment were recorded. The accompanying small lateral extension and the deflected shape of the geocell mattress indicated that it had behaved as a raft foundation to the embankment.