Effect of the Smear and Transition Zones around Prefabricated Vertical Drains Installed in a Triangular Pattern on the Rate of Soil Consolidation

Abstract

Soil disturbance caused by the installation of prefabricated vertical drains (PVDs) has a large impact on the rate of consolidation. It is essential in design to quantify this effect. In this paper, we investigate the consolidation rate of soils with PVDs installed in a triangular pattern using two-dimensional finite-element analysis with full consideration of disturbance effects. This is done by accounting for the transition zone that exists between the highly disturbed smear zone and the undisturbed zone. The hydraulic conductivity in the transition zone is assumed to increase linearly from a low value in the smear zone to the original in situ value in the undisturbed zone. The actual band shape of the PVD and hexagonal zone of influence around it are used in the analysis. In addition to soil disturbance effects, the influence on consolidation rate of the size of the smear and the transition zones, the PVD spacing, and the mandrel size and shape is also investigated. Guidelines are given for using an equivalent system, where the transition zone is replaced by an expanded smear zone producing the same effect. This equivalent-system approach allows use of existing analytical solutions that consider only the smear zone in analysis and design.