ABSTRACT
The Etruria Formation has historically been an important resource for the pottery and brickmaking industry in the Stoke-on-Trent area and was mainly exploited using opencast methods – or ‘marl holes’ as they were commonly known. These ‘marl holes’ some of which have been reported to be more than 100m deep, have been subsequently backfilled generally with non-organic pottery, brickmaking and domestic waste. This paper explores the redevelopment of land over a backfilled ‘marl hole’ at a site in Hanley, Stoke-on-Trent, Staffordshire, UK, for residential properties. The development posed a number of challenges for the design of the foundations due to the historical legacy of the site. Driven steel tubular piles were chosen as a suitable system as there is precedent with this foundation solution, which has been frequently adopted for buildings within the area. However, some of the key challenges for this site included the presence of ‘high walls’ along the edges of the opencast works where driven piles could be deviated off the sides along with the uncertainty regarding socket lengths of piles driven into the underlying solid strata. To establish a 3D ground model for the ‘marl pit’, underlying strata, piezocone tests (CPTU) were seen as the most cost-effective and practicable method of site characterisation. Using this data, piles were installed, test/production piles were installed, driven to a set/penetration into the bedrock criteria and then compared to this ground model.
