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

Vacuum preloading is a typical method used to induce consolidation settlement in clayey soils prior to construction. Vacuum pressure is used to increase effective stress in soil by decreasing the pore water pressure. This is in contrast to traditional surcharge loading, which increases effective stress by increasing the total stress on the soil. This mechanism of increasing the effective stress without increasing the total stress makes vacuum preloading a safer option if shear failure is a concern when working 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 under flexible and rigid surcharge loading conditions. Good agreement is observed between the simulated and recorded settlement vs.Time and excess pore pressure vs.Time.