Recent advances in soft ground improvement - from bumpy rides to rapid transit

Much of the world's essential infrastructure is built along congested coastal belts that are composed of highly compressible and weak soils up to significant depths. Soft alluvial and marine clay deposits have very low bearing capacity and excessive settlement characteristics, with obvious design and maintenance implications on tall structures and large commercial buildings, as well as port and transport infrastructure. Stabilising these soft soils before commencing construction is essential for both long term and short term stability. Preconstruction consolidation of soft soils through the application of a surcharge load alone often takes too long, apart from which, the load required to achieve more than 90% consolidation of these mostly low lying, permeable, and very thick clay deposits 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 consolidation by promoting rapid radial flow which decreases the excess pore pressure while increasing the effective stress. Over the past 15 years, the authors have developed numerous experimental, analytical, and numerical approaches that simulate the mechanics of prefabricated vertical drains (PVDs) and vacuum preloading, including two-dimensional and three-dimensional analyses, and more comprehensive design methods. These recent techniques have been applied to various real life projects in Australia and Southeast Asia. Some of the new design concepts include the role of overlapping smear zones due to PVD-mandrel penetration, pore pressure prediction based on the elliptical cavity expansion theory, and the rise and fall of pore pressure via prefabricated vertical drain (PVD) under cyclic loads with a new constitutive model for soft soils under cyclic loads. These recent advances enable greater accuracy in the prediction of excess pore water pressure, and lateral and vertical displacement of the stabilised ground. As a rigid inclusion, the stone column can provide reinforcement to the soft soils apart from shortening the drainage path for the dissipation of excess pore water pressure. Factors such as arching, clogging and smear effects were included in a numerical solution developed recently by the authors and the simulation results showed a good agreement with field test results. This lecture note presents an overview of the theoretical and practical developments and salient findings of soft ground improvement via PVD, vacuum preloading, as well as stone columns, with applications to selected case studies in Australia, Thailand, and China. Disciplines Engineering | Science and Technology Studies Publication Details Indraratna, B. , Balasubramaniam, A. S. , Rujikiatkamjorn, C. & Zhong, R. (2014). Recent advances in soft ground improvement from bumpy rides to rapid transit. In P. P. Rahardjo & I. Bin Haji Bakar (Eds.), Southeast Asia conference on Soft Soils Engineering and Ground Improvement: Soft Soils 2014 (pp. A1-1-A1-35). Malaysia: Universitas Katolik Parahyangan, Indonesia and Universiti Tun Hussein Onn, Malaysia. This conference paper is available at Research Online: http://ro.uow. edu.au/eispapers/3766