2009 E.H. Davis Memorial Lecture: Recent Advances in the Application of Vertical Drains and Vacuum Preloading in Soft Soil Stabilization

Professor Buddhima Indraratna

Much of the world’s essential infrastructure is built along congested coastal belts composed of highly compressible and weak soils up to significant depths. Alluvial and marine soft clay deposits have very low bearing capacity and excessive settlement characteristics, with direct design and maintenance implications on tall structures, large commercial buildings, as well as port and transport infrastructure. Stabilizing such soft soils prior to construction is essential for both short and long term stability.

Pre-construction consolidation of soft formation soils by applying a surcharge load alone often takes too long. Moreover, attributed to the low permeability and high thickness of lowlying clay deposits, the required surcharge load to achieve more than 90% degree of consolidation can be excessively high over a prolonged period. A system of vertical drains combined with vacuum pressure and surcharge preloading has become an attractive ground improvement alternative in terms of both cost and effectiveness. This technique accelerates soil consolidation by promoting rapid radial flow, decreasing the excess pore pressure while increasing the effective stress.

This E.H. Davis Memorial Lecture presents an overview of the theoretical and practical developments and salient findings of soft ground improvement via PVD and vacuum preloading with applications to selected case histories in Australia, Thailand and China.

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