Controls on the distribution of drift-filled hollows in London

Engineering works carried out in central London over many decades have unearthed a number of drift-filled hollow features which exhibit curious characteristics. They extend deep into the bedrock geology and are in-filled with disturbed superficial deposits and reworked bedrock. These features can be up to 500 m wide and more than 60 m in depth. Failure to identify them during the initial site investigation can prove costly. This presentation considers the common characteristics of the drift-filled hollows and describes the methodology used to develop a drift-filled hollow hazard susceptibility map. The map will provide planners with a broader awareness of the potential location of difficult ground conditions associated with them, thereby reducing the potential for unforeseen ground conditions through effective site investigation design. The presentation also includes a discussion of some of the likely processes associated with the formation of the drift-filled hollows.