ABSTRACT
Previous investigations have considered samples that were consolidated and restrained in onedimensional chambers during testing (Hughes & Withers 1974; Hu 1995; McKelvey 2002). The primary concern with this protocol and indeed many 1g test configurations is the variable stiffness and strength of the soil that arises due to non uniform vertical stress distribution generated as a consequence of chamber wall friction. In the
1 INTRODUCTION
1.1 Vibrated stone columns
Sites that contain unfavourable ground conditions often require treatment to enhance the mechanical properties of the deposit in order to make it fit for purpose. Vibro-Flotation is a collective term for forms of ground improvement brought about by inserting a vibrating poker into the ground, primarily Vibro-Compaction and Vibro-Replacement. The latter process is often referred to as Vibro Stone Columns and has been developed principally to reinforce soft cohesive soils and mixed fills. Soil displacement arising from forced poker intrusion and the compaction process produce a composite soil mass that has a greater average strength and stiffness than the untreated ground. In addition to improving bearing capacity and reducing compressibility, stone columns installed in a uniform grid help to homogenise variable soil properties therefore reducing the potential for differential settlement. Stone columns serve a secondary function of acting as vertical drains, accelerating the dissipation of excess pore water pressures (and associated primary settlement) from the imposed loading, allowing a foundation or floor slab to be brought into service at an early stage.
