Field instrumentation monitoring of soft soil in an offshore land reclamation project

Abstract

The Changi East Reclamation Project in the Republic of Singapore necessitated offshore land reclamation for the future airport and associated facilities. Ground improvement works in the project comprises the installation of prefabricated vertical drains and the subsequent placement of sand surcharge to accelerate the consolidation of the underlying soft marine clay. In such ground improvement projects in soft soil, the degree of improvement attained by the marine clay has to be ascertained to confirm whether the soil has achieved the required degree of consolidation to enable surcharge removal. This analysis can be carried out by means of observational methods for which continuous records of ground behavior can be monitored from the date of instrument installation. A Pilot Test Site was conducted in the reclamation site comprising of a vertical drains installation as well as a control site where no drains were installed. At the Pilot Test Site the areas with vertical drain were fully instrumented and monitored to compare the degree of consolidation of the areas close to the surcharge removal period. Instruments installed, monitored and analyzed in the Case Study Area include settlement plates, deep settlement gauges, pneumatic piezometers, electric piezometers and water-standpipes. Assessment of the field instrumentation data from vertical drain areas in the Pilot Tests Site were back-analysed by the Asaoka, Hyperbolic methods and also using pore pressure data from piezometers