Three-dimensional numerical modelling of soft ground improved by prefabricated vertical drains

ABSTRACT: A prefabricated vertical drain (PVD)-improved ground under embankment surcharge loading at the Second Bangkok International Airport was modelled using a three-dimensional finite difference program and proposed matching schemes. The matching schemes used an equivalent well radius and an equivalent permeability to account for the cross-section of band-shaped drains and the smear effect, respectively. The well resistance of the PVD was taken into account by imposing a finite discharge capacity throughout the consolidation process. The numerical method incorporating the matching schemes satisfactorily simulated the drainage behaviour of the PVD unit cell and of the full-scale PVD improved ground. The three-dimensional numerical modelling also showed that the degree of consolidation of the PVD-improved ground in terms of settlement rate was higher than that in terms of excess pore pressure dissipation rate. In addition, after the PVD improvement, the undrained shear strength of the clay layers below the centre of the embankment was numerically estimated to be approximately twice the value before the improvement.