Conventional surcharge loading to achieve soft soil consolidation has been a relatively slow process, and the combination of part surcharge and vacuum pressure with prefabricated vertical drains (PVD) has become an attractive alternative in many parts of the world. Centre for Geomechanics and Railway Engineering at University of Wollongong is one of the leading soft soil testing and ground improvement centres in the world, and the use of large scale experimental rigs, theoretical development and numerical simulations of soft clay improvement with vacuum preloading via vertical drains have contributed to significant advancement of the design techniques during the past decade.
The lecture will look at the inevitable problems of smear associated with mandrel driven PVD, the distribution of suction pressures through PVD, conceptual development of consolidation models capturing the effects of vacuum. The applications to case histories employing equivalent plane strain theory developed by Prof Indraratna and his research team will be presented and discussed. The Lecture will also address the role of PVD under cyclic loads in railway environments and the optimization of drain lengths under various circumstances. The field observations of retarded pore pressure dissipation will be interpreted in terms of drain unsaturation, high lateral strains and other factors. Finally, design procedure with associated charts for PVDs with vacuum combined surcharge pressure will be introduced.
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