Soft ground improvement via vertical drains and vacuum assisted preloading

Abstract

Application of vacuum assisted preloading is an imperative method when a considerable load is required to meet the desired rate of settlement and an increase in the undrained shear strength upon consolidation. Moreover, where lateral displacements at the edge of a coastal embankment need to be controlled, application of vacuum pressure with a cut off offers the optimum solution. To facilitate vacuum propagation, vertical drains are usually employed in conjunction. The installation of vertical drains using a steel mandrel creates significant remoulding of the subsoil surrounding the drains thereby, reducing soil permeability and adversely affecting the soil consolidation process. In this paper, the simulation of vacuum assisted consolidation using the spectral method and finite element analysis is carried out. Subsequently, the 2D and 3D numerical multi-drain analyses are conducted to predict the excess pore pressures, lateral and vertical displacements. The performance of two selected case histories at the sites of Suvarnabhumi Airport, Thailand and Tianjin Port, China are discussed and analysed. The numerical predictions are then compared with the available field data. Finally, a procedure for the design of vertical drains is presented with a worked-out example.