The thesis mainly studies consolidation behavior of the marine clay under vacuum preloading. In this study, vaccum preloading is selected as the ground improvement method. Vacuum preloading, not only shown to be cheaper and faster than surcharge fill, but also reduces the danger of bearing capacity failure. To enhance the consolidation process, prefabricated vertical drains are incorporated with vacuum preloading. Besides vacuum preloading, surcharge preloading is also performed in the soil for comparing purpose. The numerical results are modeled by a finite element program, CRISP. Modified Cam Clay and linear elastic models are adopted for different soil properties. Settlements, lateral displacements and pore water pressure are studied under vacuum preloading and compared with the results of surcharge preloading. Combination of vacuum pressure with surcharge loading has shown advantages on increasing the overall effective loading, reducing the lateral displacement of the soil, as a result improves the damages caused in the nearby building. A case study in the Terminal of Macau International Airport is also presented here. Three models under different loading condition are made for the simulation of the field settlement data provided by LECM. Model 3, with vacuum pressure varied with depth and time, gives similar results with the field data.