Consolidation of estuarine marine clays for coastal reclamation using vacuum and surcharge loading
Soft clays in coastal areas have low shear strength and high compressibility. Consequently, certain construction activities for infrastructure developments in these deposits often pose geotechnical problems due to large time-dependent settlements and lateral movements. Ground improvement techniques are adopted in such terrains to reduce the water content of soft clays by preloading with surcharge fill over vertical drains. Depending on the magnitude of the surcharge load used, substantial immediate settlement with lateral movements can take place during preloading, leading to undrained stability problems in various parts of the clay foundation. Therefore, the use of vacuum-assisted preloading has now become a popular method in ground improvement works where substantial loads need to be carried out to meet a desired rate of settlement and mitigate undrained failure by controlling lateral displacements. To assist the vacuum propagation to significant depths, vertical drains are used in tandem at the Port of Brisbane, Australia, and vacuum-assisted surcharge preloading and conventional surcharge preloading schemes were adopted to reduce the consolidation time and long-term settlement in soft Holocene clays in 2009. It is shown that a combined vacuum surcharge loading system with a standard surcharge fill highlights the obvious benefits of vacuum consolidation in reducing long-term settlement and enhanced stability.