Influence of Spatial Variability in Soft Soil and Deep-Mixed-Columns on Long-Term Settlement in Railways

Paper in proceeding, 2026

Railway tracks constructed on soft soils are susceptible to accumulated settlement under repeated traffic loading. Although deep mixed columns (DMCs) are used widely as ground improvement method to stabilise soft soils, the spatial variability of both natural and stabilised soils introduces significant uncertainty. This study investigates the influence of spatial variability in soft soils and DMC on the dynamic response and long-term settlement behaviour of railway tracks. An integrated numerical framework combining dynamic vehicle--track--soil interaction (VTSI) modelling with empirical settlement accumulation models is used. A detailed three-dimensional (3D) finite-element (FE) model is used to evaluate the equivalent substructure stiffness as input to a reduced-order two-dimensional model and dynamic response, while a reduced-order iterative model is adopted for long-term settlement prediction. The spatial variability is represented using random field modelling, and its influence is investigated through a fractional factorial design approach. The results show that DMC reinforcement reduces accumulated settlement and increases track stiffness, while increasing spatial variability in the soil and stabilised soil may lead to local differential settlements along the track alignment.