Piecewise-Linear Modeling of Combined Vacuum and Surcharge Preloading at the Second Bangkok International Airport

Abstract

Vacuum preloading is a common method to improve soft, fine-grained soil. While traditional surcharge preloading increases effective stress by increasing total stress, vacuum preloading increases effective stress by reducing pore pressure. This reduces the risk of shear failure, which can be a concern when using surcharge preloading on very weak soil. This paper presents a numerical model for large strain consolidation under combined vacuum and surcharge preloading. The model is based on a readily available radial consolidation model, known as RCS1, which is able to account for vertical and radial flow, soil self-weight, unload/reload effects, time-dependent loading, hydraulic conductivity anisotropy, soil smear, and partial prefabricated vertical drain (PVD) penetration. Additional capabilities of vacuum-induced consolidation are added to the original RCS1 to consider combined vacuum and surcharge loading. The developed model is utilized to simulate a well-published case history of combined vacuum and surcharge preloading at the Second Bangkok International Airport. Good agreement is observed between the simulated and recorded settlement vs. time and excess pore pressure versus time.