Observational method of assessing improvement of marine clay

The ongoing Changi East Reclamation Project in Singapore consists of land reclamation and ground improvement works of the foreshore for the future expansion of the Changi International airport and associated facilities. Reclamation works in the project involve the hydraulic placement of sand-fill over the seabed, which is underlain by thick, highly compressible Singapore marine clay. Ground improvement works in the project comprise the installation of vertical drains and the subsequent placement of surcharge to accelerate the consolidation of the underlying marine clay. A pilot test site was carried out in the project, comprising three sub-areas that were installed with vertical drains at various spacings, plus a fourth untreated sub-area. The four sub-areas were surcharged simultaneously and preloaded for a duration of 32 months. A comprehensive field instrumentation programme was implemented in the pilot test site, comprising settlement plates, deep settlement gauges, piezometers and water standpipes. The degree of improvement attained by the foundation soil at each sub-area was determined and assessed during the process of consolidation and 32 months after surcharge placement using the observational method. This paper describes the applications and comparisons between the Asaoka method, the hyperbolic method and piezometers in monitoring the improvement of marine clay under reclamation fills.