Prefabricated vertical drains with preloading option are the most widely-used ground improvement method for the improvement of marine clays in land reclamation projects. The assessment of the degree of consolidation of the marine clay is of paramount importance prior to the removal of preload in such ground improvement projects. This analysis can be carried out by means of piezometer monitoring. Piezometer monitoring data can be analysed to obtain the degree of consolidation of the improved marine clay. Back-analysis of the piezometer data will also enable the coefficient of consolidation due to horizontal flow to be estimated. Factors that affect the analysis of piezometers include period of assessment, hydrogeologic boundary condition, settlement of piezometer tip and reduction of initial imposed load due to submergence effect. The aim of this paper is to highlight the significance and impact of the various factors that affect assessment by the piezometer monitoring method.