Achieving sustainability in vibro stone column techniques

As part of achieving environmental sustainability in ground treatment, there is an increasing desire to use recycled materials for vibro stone column techniques. Materials used in stone column construction are required to be free-draining, hard, inert and comply with acceptable criteria in terms of material type, grading, hardness and chemical stability. Spent railway track ballast and crushed concrete probably have the greatest potential for this application in the UK. New European standards for aggregates allow the use of environmentally sustainable materials in a wider range of applications than under the British Standards they replace. However, where such materials are considered for use, as an alternative to natural primary aggregates, it is important that these materials are fit for purpose. Technical requirements for vibro stone column aggregate are discussed. Of particular importance is the fines (clay/silt) content of the aggregate, as this can have a significant effect on the angle of internal friction of the stone column material (and drainage characteristics). This in turn influences both the carrying capacity of the stone column and the settlement characteristics of the stone column-soil composite. Some applications of recycled aggregate in the context of vibro stone columns are presented, including a case history for spent railway ballast and crushed concrete. Also presented is an innovative technique for avoiding pollutant linkages via stone columns using ‘vibro concrete plug’ technology.