The installation of drains creates a disturbed region known as a smear zone where the change in the clay structure affects the horizontal permeability and compressibility. The parameters required to characterise the smear effect are the extent of the smear zone and the ratio of the horizontal coefficient of permeability in the undisturbed zone and in the smear zone. Only limited studies have been carried out on different aspects of soil disturbance due to driving vertical drains and its effects on the subsequent consolidation. In this paper the disturbed zone around a rectangular mandrel was characterised using soil samples obtained from the soft clay layer at various locations beneath an embankment built at Ballina, Australia, where vertical drains were installed. By determining the change in the coefficient of permeability, the water content and volume compressibility across the smear zone, the effects of soil disturbance on consolidation due to the installation of drains can be quantified using the available numerical model. Disciplines Engineering | Science and Technology StudiesThe installation of drains creates a disturbed region known as a smear zone where the change in the clay structure affects the horizontal permeability and compressibility. The parameters required to characterise the smear effect are the extent of the smear zone and the ratio of the horizontal coefficient of permeability in the undisturbed zone and in the smear zone. Only limited studies have been carried out on different aspects of soil disturbance due to driving vertical drains and its effects on the subsequent consolidation. In this paper the disturbed zone around a rectangular mandrel was characterised using soil samples obtained from the soft clay layer at various locations beneath an embankment built at Ballina, Australia, where vertical drains were installed. By determining the change in the coefficient of permeability, the water content and volume compressibility across the smear zone, the effects of soil disturbance on consolidation due to the installation of drains can be quantified using the available numerical model.

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When vacuum preloading is applied with vertical drains, the rate of consolidation can be increased, and the stability of an embankment is enhanced due to the inward lateral movement. The aim of this study is to develop an analytical solution for vacuum preloading that accurately captures the more realistic variations in compressibility and permeability in actual ground conditions as a result of drain installation. The soil samples were obtained from various locations after drain installation to determine the characteristics of soil surrounding the vertical drain in terms of compressibility and permeability. The main differences between the proposed and conventional models are described by considering the stress history and preloading pressure. The effect of pre-consolidation pressure and the magnitude of applied preloading are examined through the dissipation of average excess pore pressure and associated settlement. The analysis of a selected case history employing the writers’ solution indicates improved accuracy of the predictions in comparison to the field measurements.

Class A and C predictions for Ballina trial embankment with vertical drains using Class A and C predictions for Ballina trial embankment with vertical drains using standard test data from industry and large diameter test specimens standard test data from industry and large diameter test specimens

Over the past decade, the application of vacuum preloading for stabilising reclaimed soil and other low-lying estuarine soils has become popular in Australia. Its cost effectiveness is a governing factor in view of the reduced consolidation time to achieve a relatively high degree of consolidation. Due to demand in trade activities at the Port of Brisbane, new port facilities have been constructed on reclaimed land. A vacuum and fill surcharge, in conjunction with prefabricated vertical drains, was selected to accelerate consolidation time of the thick layers of subsoil. A performance comparison of a combined vacuum and fill surcharge loading system with a standard surcharge fill highlights the clear advantages of vacuum consolidation. Field data demonstrate how the embankment performed during construction. This paper also assesses the relative performance of the two contrasting preloading systems (i.e. vacuum and non-vacuum system).