Geophysical investigation and in-situ treatment of collapsible soils

Meta-stable soils (i.e. those prone to collapse) occur worldwide, resulting in soil collapsibility being a global problem. Such soils can be naturally occurring or man made, and loess, one of the most common natural collapsible soils (often found underlying areas of infrastructure) covers over 10% of the Earths surface. In-situ properties are often variable and difficult to predict, so effective site investigation is essential for the optimum characterisation and prediction of soil behaviour, and for the planning of ground improvement strategies prior to development of such sites. Recent work has shown the potential of geophysical methodologies to provide useful information on collapsible soils, overcoming some of the limitations of purely geotechnical ground investigations. New developments have also been made concerning techniques used for the subsequent ground improvement of such sites. This paper outlines the problems associated with collapsible soils and, using case studies from the UK and Africa, highlights the potential of geophysical seismic and resistivity methods to successfully investigate soil properties, including assessment of ground improvement work. The paper also presents an example of recent fieldwork from Eastern Europe where a new dynamic compaction methodology has been successfully used for ground improvement on collapsible soil.