by Keith Emmett, department of civil and structural engineering, The University of Sheffield. This paper was first published in GE’s December 2005 issue.
Redevelopment of sites that have previously been used for domestic or industrial purposes is becoming increasingly necessary and desirable. However, many of these sites contain contaminants in the upper soil strata.
The danger of spreading these insitu pollutants is an issue facing engineers when designing deep foundations such as piles.
The Environment Agency has identified the risk of piling on brownfield sites and the creation of flow paths that it may cause, allowing contaminated groundwater to move through low permeability layers into underlying aquifers (Environment Agency, 2001).
There is a lack of research and monitoring data on contaminant migration through layered ground. Some preliminary work was carried out by Hayman et al (1993). Solid cylindrical and wooden piles were driven through a layered ground model containing a thick intermediate clay layer, equivalent to 60 pile diameters. Results showed that the clay would seal the edges of the piles, preventing the creation of preferential flow paths.