Numeric modelling of vertical drains: two- and three-dimensional analyses

This paper compares two-dimensional (2D) with three-dimensional (3D) water flow modelling used to predict the behaviour of an embankment built on a soft soil improved with prefabricated vertical drains. The three-dimensional analysis is performed considering the field pattern of the vertical drains, whereas in the two-dimensional analyses the verticals drains are simulated in two ways, using an equivalent overall permeability and considering the draining walls. The numerical predictions are compared with one another and with the field data in terms of settlement, horizontal displacement and excess pore pressure. The two-dimensional analyses provide similar results to the three-dimensional modelling in terms of settlement and horizontal displacement. Naturally, the time evolution of the excess pore pressure depends on the drainage conditions, which differ in the cases studied. In general, it is concluded that the use of two-dimensional modelling, employing an equivalent overall permeability, is sufficiently accurate for practical applications.