A bonded elasto-plastic soil model is employed to characterize cement-treated clay in the finite element analysis of an excavation on soft clay supported with a soil-cement slab at the bottom. The soft clay is calibrated to represent the behaviour of Bangkok soft clay. A parametric study is run for a series of materials characterised by increasing cement content in the clay-cement mixture. The different mixtures are indirectly specified by means of their unconfined compressive strength. A similar parametric analysis is run in parallel using a linear elastic-perfectly plastic model for the clay-cement. Results from both series of analysis are compared highlighting the differences in predicted behaviour of the retaining wall and the excavation stability.