Concrete was encountered in some of the boreholes at the interface of the chalk and overlying granular drift deposits. Significant coarse flint gravel inclusions and possible bands of flint gravel and cobbles together with sandy and chalky material were encountered with the concrete. Based on the findings of the intrusive investigation and results of the test piles, it is considered that the concrete loss recorded may be associated with a band of flint gravel and cobbles present at the interface of the Upper Chalk and overlying granular materials at depth.
The bands of flint were found to be extensive across the site and as a result it was recommended to complete a grouting exercise at the proposed pile locations using a ‘weak’ grout mix and then pile through the grout to avoid further significant concrete losses during piling.
The pile arrangement for the development was to be reviewed to avoid contact with the concrete from failed piles which had formed obstructions.