This paper investigates the behaviour of deep cement mixed (DCM) column improved ground during the breakage of soil-cement structure and subsequent consolidation incorporating the strain softening behaviour of cement mixed soils beyond yield. Numerical simulations were carried out using an extended version of the Mohr-Coulomb model. The ability of the numerical model in replicating the breakage of soil-cement structure was investigated using the physical model tests reported by Horpibulsuk et al. (2012) considering single cement mixed columns embedded in soft Bangkok clay. Numerical results clearly show that the sudden increase in settlements observed during the physical tests at higher applied loads is due to breakage of soil-cement structure during strain softening. During the strain softening, loads previously supported by DCM columns are transferred to the surrounding soft clay and excess pore pressures generated within the soft clay had shown a significant increase. Using the same model, the consolidation behaviour of the improved ground is investigated by varying the permeability of columns with respect to the surrounding soil. Results show that DCM columns will improve the consolidation behaviour of improved ground even when the column permeability is less than the permeability of surrounding clay due to higher coefficient of consolidation of columns compared to soft clay.