20th Oct 2021 17:30 hours
The Great Hall, Sherfield Building, Imperial College London, Exhibition Road, SW7 2AZ
The British Geotechnical Association (BGA) is pleased to announce that the 60th Rankine Lecture will be given by Professor Stephan Jefferis of Environmental Geotechnics Limited on The Unusual and the Unexpected in Geotechnical Engineering: Observation – Analogy – Experiment.
The event will be webcast live. A viewing link will be available on the day of the event via this web page.
The British Geotechnical Association (BGA) would like to take the opportunity to reassure attendees that we are closely monitoring the situation regarding Coronavirus but currently plan for the Lecture and Dinner to go ahead as an in person event, subject to prevailing Government guidelines at the time. We trust that everyone planning to attend the Lecture and Dinner will consider their position in relation to any potential risk they might pose to others and ask them to act responsibly. Dinner hosts are asked to consider their guests' position in relation to government health warnings. We all have a duty of care to others and trust that everyone will act with that in mind.
The Rankine Lecture is widely viewed as the most prestigious of the invited lectures in geotechnics. It commemorates William John Macquorn Rankine, Professor of Civil Engineering at Glasgow University, who was one of the first engineers in the UK to make a significant contribution to soil mechanics. He is best known for his theory for the earth pressure on retaining walls.
The Rankine Dinner is held after the lecture. The Dinner is currently fully subscribed.
The 60th Rankine lecture will explore a wide range of processes which have substantial consequences in geotechnical engineering and yet have received little formal attention.
The lecture will first examine the behaviour of support fluids used in piling, diaphragm walling, tunnelling and horizontal directional drilling – processes which have been strongly influenced by analogies with oil well drilling operations. However, the role of the support fluid in each of these applications is different and it would be a mistake to assume that the key properties are the same for all of them. For example, for decades it was assumed that an excavation support fluid must form a filter cake and should be markedly denser than the surrounding groundwater. The advent of polymer support fluids, which may have little tendency to form a filter cake and have near water densities, has shown these assumptions to be simplistic.
From support fluids, the next step is to consider slurry trench cut-off walls and then the impact of geotechnical activities on soils more generally. On careful analysis, it is apparent that many of the natural processes that occur in soils are mediated by micro-organisms. This adds new dimensions of complexity as there can be multiple outcomes. Construction processes that influence microbiological activity include heating/cooling, tunnelling, dewatering, flooding, sealing with liners, grouting and other introduction of chemicals. These are processes that we regularly undertake without a second thought for their potential microbiological consequences. Fortunately, these usually pass unnoticed and innocuously but occasionally, as will be shown, the effects are at the least unexpected!
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.
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.