Events & Courses

CPD Geohazards Lecture Series presents Problematic Soils - Swell/Shrink Soils by Peter Hobbs BGS

Start time: 17.00 hrs

Shrink-swell soils and rocks constitute some of the most costly and widespread geological hazards globally, with costs estimated to run into several billion pounds annually. These engineering materials present significant geotechnical and structural challenges to anyone wishing to build on, or within, them. Shrink-swell occurs as a result of changes in the water content of soils (and rocks) containing clay minerals. This is reflected in a change in volume of the ground through shrinking or swelling. Swelling pressures can cause heave, or lifting, of structures on the surface and excavations below ground whilst volume changes due to shrinkage can cause differential settlement at or near the surface.

Many major towns and cities worldwide are founded on clay-rich soils and rocks, upon and within which their infrastructure, buildings and underground services are constructed. In the UK the effects of shrinkage and swelling of clay soils and rocks, with respect to foundation and building damage, were first recognised by geotechnical specialists following the dry summer of 1947. After the drought of 1975–76 insurance claims in the UK came to over £50 million, and since then the cost of this has risen dramatically. In 1991, after a preceding drought, claims peaked at over £500 million. Over the past 10 years the adverse effects of shrink-swell behaviour has cost the economy an estimated £3 billion, making it the most damaging geohazard in Britain today, with as many as one in five homes in England and Wales at risk from ground that swells when it gets wet and shrinks as it dries out, despite the UK’s temperate climate resulting in reduced risk compared with many other countries.

This lecture aims to present the viewer with a basic understanding of shrink-swell soils. To do this, I will review their nature and distribution and describe the basic processes of swelling and shrinkage. Finally, I will discuss how these soils are sampled and tested in the laboratory, relationships with Atterberg Limits and what strategies are available for their management in an engineering environment.

Speaker - Peter Hobbs BGS

Peter Hobbs is an Engineering Geologist with 46 years’ experience at the British Geological Survey (BGS).  He manages the ‘Slope Dynamics’ project which monitors long-term landslide behaviour at the BGS’s Coastal Landslide Observatory (CLO) at Aldbrough using state-of-the-art surveying and slope stability techniques. He has acted as geotechnical specialist on marine drilling cruises (including ODP), technical co-ordinator for NIREX core characterisation projects and on ‘formation expert’ panels to HS2. Peter has developed laboratory geotechnical equipment for soils and rocks, including research on clay swelling and shrinkage and the tensile strength of ‘extremely weak’ rocks. He has worked extensively on landslide mapping, monitoring and research both in the UK and overseas, at regional and site-specific scales. Peter has led and co-authored works on the engineering geology of major UK clay and mudstone formations including the Gault, Lias and Mercia Mudstone, and contributed to BGS’s ‘National Geotechnical’ and ‘Landslide’ Databases and the ‘Geosure’ system for geohazard classification. Peter has also worked on major overseas research projects on the geotechnical properties of tropical clay soils in Indonesia & Kenya and the establishment of geotechnical testing laboratories in Cyprus and Jamaica. Peter has developed innovative laboratory equipment for testing clay-bearing soils and rocks and has provided consultancy on numerous slope stability and route planning assessments for various commercial engineering and infrastructure companies and NGO’s in the UK. Peter has contributed to three GSL Special Publications, including that on ‘Clay Materials used in Construction’ and authored 90 papers and over 100 commissioned reports with more than 60,000 web downloads of BGS publications to which he has contributed.

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