The geotechnical engineer may be forgiven for seeking to ignore chemical and microbiological processes in the ground. After all their physical behaviour of soils is complex enough to tax the best minds. However, soils are not inert and just occasionally chemical, and importantly natural microbiological, processes are sufficient to impact on construction work. Impacts typically occur as a result of changes in the local in-ground environment and have been associated with tunnels, grouting, soil stabilisation, water wells. Reactions in the ground can be slow and so impacts may not be seen for years but in turn may continue for years. This lecture will present a broad selection of short case histories where the impacts were sufficient to damage structures or stop work. The lecture will focus on the investigations and impacts rather than chemistry and microbiology though there will be mention of energy sources for microbiological processes and hence the movement of electrons and so redox and speciation (as a trivial example, the oxidation of Fe²⁺ soluble to Fe³⁺ insoluble).Species considered will include arsenic, carbon, hydrogen, iron, nitrogen, sulphur and also unanticipated behaviours of recycled, secondary and soluble materials.

The lecture will not consider the problems of manmade contamination in land nor processes such as microbially induced carbonate precipitation for which there is already a substantial literature.

Stephan Jefferis is a director of Environmental Geotechnics Ltd, a company he established in 1982 anticipating developments in this area. He is a Visiting Professor in the Department of Engineering Science at the University of Oxford. He is a former Chairman of the BGA and was a founder director of WJ Groundwater.

In 2022, Professor Jefferis was the 61st Rankine Lecturer.

Stephan has worked on major projects across the World including dams, tunnels, shafts and deep foundations. He has over 45 years experience in the investigation and resolution of unusual and unexpected geotechnical problems, often associated with natural chemical and microbiological processes. He has worked on geotechnical processes including fluid supported excavation for decades and is co-author of the book Polymer Support Fluids in Civil Engineering.