Optimal Design of Vertical Drains in Soft Ground


Abstract

This project is concerned with the design of a program to calculate the optimal solution for geotechnical problems involving the consolidation of soft ground by the use of prefabricated vertical drains. The effects being taken into account include smear, well resistance, ramped loading and multiple layers. The program has allowed the author to complete a series of parametric studies into the effects of the factors which contribute to the rate of consolidation using vertical drains. The final solution is a distributable program that uses an intuitive graphical user interface. This allows the user to input soil parameters and assumptions and then run the program to find the optimal spacing of drains to achieve a given consolidation in a given time. An element of probabilistic analysis has also been incorporated into the program to allow the creation of risk to cost curves for any parameters. This allows the user to make an educated decision based on the allowable cost and the degree of certainty in the soil parameters.








1 INTRODUCTION

The aim of this project is to provide a valuable tool for the design of vertical drains in practice, with the emphasis being on the combination of an accurate prediction of consolidation settlement and the ease and speed of use. In practice currently there are two feasible approaches to the design of vertical drains. Firstly to use simple design tools and methods based on basic assumptions (such as a single homogenous layer) to calculate the consolidation then interpolating between different methods to gain a more informed estimate of the settlements. The second option is reserved for projects that have little tolerance (such as nuclear power plants), which involves using a finite element or difference program to calculate the settlements. This second method is much more time consuming, and many more of the soil parameters are required. In practice generally the first option is used. The aim of this project is to fill the void between the two methods to give a quick estimate of the settlements with the minimal amount of required information and time. The factors that are going to be taken into account in this project are Ramped Loading, Smear, Well Resistance and Multiple Layers.


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