Analytical and numerical solutions for soft clay consolidation using geosynthetic vertical drains with special reference to embankments

Good quality geologic materials for construction are also becoming scarce. Due to these reasons and because of the environmental restrictions on certain public works, ground improvement is becoming an essential part of infrastructure development. As a result, Civil Engineers are forced to utilise even the poorest soft clay foundations for buildings, highways and railway tracks. Therefore, the application of prefabricated vertical drains with preloading has now become common practice and one of the most effective ground improvement techniques. The classical solution for vertical drains (single drain analysis) has been well documented in the literature, where there are many vertical drains, a true 3-D analysis of the site becomes very difficult. Therefore, equivalent 2-D plane strain models have been employed, using the methods of geometric and permeability matching concepts. The equivalent plane strain solution can now be used as a predictive tool with acceptable accuracy as a result of the significant process that has been made in the past few years through rigorous mathematical modelling and numerical analyses. In this paper, the equivalent 2-D plane strain solution is described which includes the effects of smear zone caused by mandrel driven vertical drains. The equivalent (transformed) permeability coefficients are incorporated in finite element codes, employing the modified Cam-clay theory. Numerical analysis is conducted to predict the excess pore pressures, lateral and vertical displacements. Two case histories are discussed and analysed, including the sites of Muar clay (Malaysia) and the predictions are compared with the available field data. The research findings verify that the impact of smear and well resistance can significantly affect soil consolidation, hence, in order to obtain reliable consolidation predictions, these aspects need to be simulated appropriately in the selected numerical approach.