Piezometer measurements of prefabricated vertical drain improvement of soft soils under land reclamation fill

Piezometers are commonly used for monitoring the dissipation of pore water pressure and therefore determination of degree of consolidation of soft soils after ground improvement in land reclamation projects. This paper compares the degree of consolidation obtained using pore pressure monitoring data from vibrating wire piezometers and pneumatic piezometers installed in a test site in the Changi East Reclamation project in Singapore. The test site consisted of a vertical drain sub-area at which prefabricated vertical drains were installed at 2.0 m x 2.0 m square spacing as well as an adjacent control sub-area where no prefabricated vertical drains were installed. Pneumatic piezometers were installed at the same elevations as the vibrating-wire piezometers in both sub-areas for comparison purposes. During the surcharge period of 32 months, the piezometer monitoring data were analysed at various periods to determine the degree of consolidation of the underlying soft marine clay. The degree of consolidation values interpreted from both types of piezometers was compared and with predictions from neighbouring settlement plates to evaluate their performance. The findings of the comparison between pneumatic and electric vibrating-wire piezometers indicate that both types of piezometer are suitable for monitoring the consolidation behaviour of soft soil under land reclamation fills.