Finite element modeling of soft ground with PVD under vacuum and embankment preloading

Abstract

In this study, a finite element (FE) model is employed to analyze consolidation and lateral displacement of soft ground with prefabricated vertical drain (PVD) under embankment preloading. A two-dimensional idealization is used for simplicity. Modified Cam-Clay model is used to idealize the soft ground. An equivalent permeability, based on the equal discharge rate in the model and in the field, is used to characterize flow. Field vacuum pressure is simulated by specifying negative pore pressure-time history on the PVD boundaries and sand blanket. Varying the negative pressure inputs, several FE simulations are performed to predict the field behavior of a full-scale test embankment constructed on soft clay at the new Bangkok International Airport in Thailand. An excellent agreement between the predicted and measured settlement, pore pressure and lateral displacement is obtained. Once the validation of the FE model is ensured, it is then employed to study the effectiveness of vacuum and embankment preloading on the consolidation and lateral displacement of soft ground with PVD. The vertical settlement at the centerline of the embankment is found to increase by 175% due to vacuum preloading. The lateral displacement at the toe of the embankment exhibits a decrease of about 64% due to vacuum preloading. The undrained shear strength of the soft ground with PVD is significantly (1.7 times) more than the initial undrained shear strength of the soft ground without PVD. Further simulations are carried out to determine an equivalent embankment without vacuum. Results show that vacuum preloading employed at this site yields only 40% of the vacuum applied at the pump station, which is a concern for efficient vacuum application. The developed FE modeling and findings of this study are expected to be useful to design engineers involved in the construction of embankments on soft ground.