The deep excavation failure during the MRT construction at Nicoll Highway, Singapore, serves as a critical case study in the field of geotechnical engineering. This research aims to re-evaluate the incident by focusing on the influence of residual excess pore water pressure on the stability of deep excavations in under-consolidated marine clay, using a soil model calibrated with post-failure CPTu data. The model is assessed by comparing predicted wall deflections with actual inclinometer monitoring data. The results indicate that undissipated excess pore water pressure or incomplete soil consolidation significantly reduces the shear strength of marine clay, thereby increasing the risk of deep excavation failure. Additional contributing factors include the incomplete implementation of structural supports such as struts and jet grout piles, as well as the sloping profile of the hard soil layer that formed a valley-like geometry. These aspects played a substantial role in the instability observed in the Nicoll Highway case.