Radial consolidation theories and numerical analysis of soft soil stabilisation via prefabricated vertical drains

In this paper, an analytical solution based on actual radial soil permeability and compressibility is proposed considering the impact of parabolic variation of permeability in smear zone. The use of the spectral method for multilayered soil consolidation is introduced and verified. The Cavity Expansion Theory is employed to predict the extent of soil disturbance (smear zone) caused by the installation of mandrel driven vertical drains. The smear zone prediction is then compared to the data obtained from large-scale radial consolidation tests. Furthermore, the advantages and limitations of vacuum application through vertical drains are discussed using the proposed solutions. The applied vacuum pressure generates negative pore water pressure, resulting in an increase in effective stress within the soil, which leads to accelerated consolidation. Vacuum pressure is modelled as a distributed negative pressure (suction) along the drain length and across the soil surface. Analytical and numerical analyses incorporating the Authors’ equivalent plane strain solution are conducted to predict the excess pore pressures, lateral and vertical displacements. Application of the theoretical models for a selected case history is discussed and analysed, at the site of the 2nd Bangkok International Airport. The predictions are compared with the available field data, showing that an equivalent plane strain model can be used confidently to predict the performance with acceptable accuracy through rigorous mathematical modelling and numerical analysis. The research findings verify that the role of smear, drain unsaturation, and vacuum distribution can significantly affect the soil consolidation, hence, these aspects need to be modelled appropriately to obtain reliable predictions.