At 06:50 on Monday 14 th August 2017, a hillslope on the Freetown Peninsula, Sierra Leone, collapsed, sending 300,000 m 3 of debris into the flooded valley below. As this debris mixed with floodwater it became a sediment-laden flood which entered a drainage channel and travelled 6 km to the coastline. The event destroyed nearly 400 buildings, claimed the lives of an estimated 1,100 people and affected approximately 5,000 people. The mechanism was a two-stage rainfall-triggered landslide followed by a channelised debris-laden flood. The processes were similar to the nearby 1945 event in Charlotte, which killed at least 13 people.
This chapter provides an introduction to the Engineering Group of the Geological Society of London (EGGS) Working Party book on the engineering geology and geomorphology of glaciated and periglaciated terrains. A summary of changes in the extent of glacial and periglacial conditions throughout the Quaternary to the present day is provided initially. The engineering difficulties associated with working in glaciated and periglaciated terrains are demonstrated through the inclusion of seven important case histories. The chapter then discusses the background to the Working Party, the scope and structure of the book, including abstracts of each chapter, before finally guiding the reader on how the book may be used at a site where glacial or periglacial conditions had formerly prevailed. In particular, the importance of updating the ground model at each stage of the project as an approach to risk management is emphasized.
In 2012 the Engineering Group of the Geological Society of London established a Working Party to undertake a state-of-the-art review on the ground conditions associated with former Quaternary periglacial and glacial environments and their materials, from an engineering geological viewpoint. The final report was not intended to define the geographic extent of former periglacial and glacial environments around the world but to concentrate on ground models that would be applicable to support the engineering geological practitioner. Key aspects of ground condition uncertainty would be addressed and developed within these ground models.
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