Numerical modelling capturing the behaviour of reinforced soft ground for public transport infrastructure

Foundations on soft soil without proper ground improvement can initiate excessive settlement causing undrained failure of infrastructure. Amongst various ground improvement techniques, reinforcement by stone columns is one of the convenient and effective methods, with numerous advantages including: increased bearing capacity, reduced settlement, improved slope stability and liquefaction control. The stone columns not only act as vertical stiffening members increasing the overall bearing capacity of soft ground while reducing the overall settlement, they also assist in effective radial consolidation. The existing analytical and numerical solutions to predict the behaviour of reinforced soft ground, the models are based on equal strain hypothesis aided with linear void ratio-effective stress correlation, and therefore incapable of capturing the special considerations relevant to transport infrastructure. The authors have developed a novel numerical model based on Finite Difference Technique to analyse the response of stone column reinforced soft soil supporting public transport infrastructure, adopting a free strain hypothesis and also considering arching, clogging and smear effects aided with effective stress dependant soft soil compressibility. The model has incorporated the stiffening effect of the columns as well as accelerating the consolidation by radial drainage. Apart from predicting excess pore water pressure dissipation and resulting settlement, the load transfer mechanism and degree of improvement were captured by the model. The predictions of the model were compared to the results obtained from a full-scale trial embankment construction at the Australian National Field Testing Site at Ballina, NSW, Australia.