I read with interest the March issue on piling and deep foundations, but was disappointed to see no mention of ground improvement techniques. These provide a particularly efficient foundation solution and current emphasis on brownfield redevelopment will see an increase in their use. Its application also brings the process full circle.
Vibro stone column techniques first came to prominence in the UK in the early 1960s in the inner city areas of Glasgow and Manchester where the process was judged suitable for dealing with the problem of rubble filled cellars in slum clearance areas and housing redevelopments.
Here, the vibro displacement dry top feed technique was commonly used, the object being to 'stiffen' the existing fill and provide more uniform ground conditions thus reducing total and differential settlement.
Thirty and forty years later, a new generation of re-development is taking place on some of these same sites and vibro stone column techniques are still proving to be the popular choice of ground treatment.
The fundamental components of vibro equipment have changed very little over the years, although there have been continuing modifications and improvements to the equipment to improve power output and reliability.
The vibro displacement dry top feed technique of stone column formation in granular and heterogeneous fills continue to be a popular choice providing bores remain stable during stone column construction.
The 1970s and 1980s saw the development of dry bottom feed vibro displacement technology which provided an alternative for dealing with weak ground conditions (especially silty and clayey soils combined with shallow groundwater) and where bore stability is an issue.
With increasing emphasis on the development of brownfield sites and the environmental concerns over the use of the wet technique on contaminated sites, in particular, demand for dry bottom feed techniques has increased.
However it should be recognised that for certain ground types, where contamination is not an issue, the wet technique may be more suitable and often necessary to achieve satisfactory results.
Colin J Serridge technical manager Bauer Foundations (UK)