Consolidation of soft soil by means of vertical drains: field and laboratory observations

Abstract

Prefabricated vertical drains (PVD) in combination with pre-loading have become a popular method of soil improvement in Australia as it provides an effective and low cost solution to the problems of soft soil. A few large-scale trial embankment tests have been performed in the Brisbane and Sunshine Coast areas in the past decades to explore the feasibility of using PVD techniques for construction of high speed motorways on soft soil foundations in Queensland. Although satisfactory performance was observed in several trials, the effectiveness of vertical drains was not fully assessed as the varying geologic conditions as well as the design features of the embankment trial, which may have affected the integrity of the field data, were not controlled for. This paper seeks to provide laboratory data that can be used for assessment of the effectiveness of ground improvement methods, which may reduce the cost of large-scale field projects. The experimental program was designed to study the effect of vertical drains on settlements of soil under different stress levels. It was found that the process of consolidation occurred more rapidly when vertical drains were installed, however it can vary depending on the size of drain and the smear effect. In addition, data from a large-scale trial at the Sunshine Coast Motorway were reviewed to provide a better understanding of the effect of PVDs on the improvement of soft soil characteristics.