Recently, the need for geosynthetic-reinforced column-supported (GRCS) embankment widening over soft soil has been increased. Current design methods result in large differences in design requirements and therefore are difficult to be used in practice. Instead, numerical methods have been employed to understand the behaviour or performance of the GRCS embankment during and after widening. Most of the previous numerical studies have used the Mohr-Coulomb model for soft soils (i.e. not the Modified Cam Clay model), which cannot reflect the effect of consolidation on the properties of the soils. However, the generation and dissipation of excess pore water pressure under GRCS embankments during and after construction make their behaviour time-dependent. A two-dimensional (2D) parametric study using the Modified Cam Clay model based on coupled hydraulic and mechanical modelling was developed in this study to investigate the time-dependent behaviour of GRCS widening embankments under different conditions. Special attention was paid to the influence of several key factors on the performance of the embankments as indicated by maximum settlements and the tension in the geosynthetic. The investigated key factors include the variations of the length of columns, permeability of the soft soil, elastic modulus of columns, tensile stiffness of the geosynthetic, and service time after the construction of the existing GRCS embankment. These factors are discussed and concluded based on the degree of importance in this study. The study showed that although the length of columns under widening has been decreased by a percentage of 25%, there is no increment of immediate settlement at the crest.