Abstract: Within the UK, high population density and increased traffic volumes has led to the expansion of urban areas incorporating new building construction and associated infrastructure. Such developments have encroached on ?brownfield? sites with a legacy of former industrial activity and ?marginal sites? where weak alluvial and/or glacigenic deposits occur. Dependent upon site geotechnical characterisation, this has necessitated the use of ground improvement techniques prior to construction. A brief overview is provided of one of the most widely used ground improvement techniques within the UK urban environment, namely that of (vibro) stone columns, in particular how the technique has developed in response to environmental legislation/pressure and requirements for improved performance and sustainability. The importance of detailed site investigation for stone column design in the urban environment is emphasised.
The main part of this paper then focuses on the novel application of vibro stone column (vsc) and vibro concrete column (vcc) techniques beneath new highway embankment construction over soft ground and the steps required to permit successful ground improvement implementation. This draws upon recent experiences on the M60 orbital motorway widening around south Manchester and a new relief link road construction in Kings Lynn, Norfolk (UK).
The most common types of ground related problems encountered during ground improvement relate to soil strata interfaces and boundaries (i.e. geometry not as anticipated) and the geotechnical properties of the soil profile. The usefulness of CPT (CPTU) testing as a site investigation tool, the importance of preliminary trials (particularly for larger projects), quality control, monitoring and testing, to ensure successful implementation and performance of the treated ground is emphasised.
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