Robert Gibson

Robert Edward Gibson, Emeritus Professor of Engineering Science at King's College London, died in Worthing, Sussex, England, on 23 December 2008.

Bob, as he was widely known, was born on 12 May 1926 in Felpham, Sussex. He attended Emanuel School, then spent one year at Battersea Polytechnic before transferring to Imperial College to study civil engineering. He was 19 years old when he completed his BSc in engineering. After brief spells at RAE Farnborough and in the Chief Scientific Advisor's Division at the Ministry of Works, he returned to Imperial College to work for a PhD. He was supervised by Profesor Alec Skempton and, after completing his doctorate, remained for a further three years at Imperial College before moving to the Building Research Station in 1953. By 1956 he was back at Imperial, first as a lecturer, then as a Reader, and he moved in 1965 to Kings College London, where he took up a Chair in Engineering Science in 1967, a year after he had received a DSc. He took on various consulting projects parallel with his academic research, and became a Principal at Golder Associates, involved in a variety of projects in North America and the UK. His combination of academic and practical strengths was recognised in the award of an Industrial Fellowship at Wolfson College, Oxford from 1983–1985.

His lasting contributions to geotechnics have been largely due to his passion for mathematics and his ability to develop analytical formulations that could be applied to real engineering problems. He was one of the few researchers whose name is linked to a particular soil model, so that geotechnical engineers across the world recognise a Gibson soil as one in which the stiffness increases linearly with depth. Before this pioneering work was published in the 1960s, the analytical solutions used for foundation design assumed that the stiffness was constant with depth, an assumption that, generally, was far from realistic. In his other major contribution to civil engineering design, he presented an analytical solution to the consolidation behaviour of very soft soils, allowing the inclusion of self-weight as a consolidating force, without the previous constraint that overall strains were small. As construction took place on more difficult ground, and as land reclamation increased, this work became increasingly important, and it continues to be the basis of many current design projects.

In the early days at the Building Research Station, he worked with John McNamee, a mathematician, and this association helped to develop Bob's mathematical insight. They tackled a number of problems of seepage, consolidation and deformation that had previously seemed intractable. A collaboration with W. G. Bickley led to a book on the use of vectors and tensors. He had a long-established friendship and collaboration with Robert (Bob) Schiffman, at the University of Colorado, where Schiffman was Professor of Civil Engineering and Gibson held the position of Adjunct Professor. Schiffman was a pioneer in computer applications, and, together with his students, brought numerical capabilities to their joint research, thus extending the application, especially, of Gibson's work on finite strain consolidation.Fig. 1 

Bob's contributions have been in the application of elastic, visco-elastic and plastic models to the description of the time-dependent behaviour of soils encompassing primary and secondary consolidation. His ability to solve the complicated equations involved was crucial, but his success was due to his engineering sense and a strong feeling for the way in which soil would behave, as well as in his mathematics. He defined real soil behaviour so that it could be tackled mathematically, thus allowing improved predictions to be made, both for the design of projects such as earth dams, and in the interpretation of new instruments such as the pressuremeter. He was particularly interested in pore pressure. On the practical side, he studied the influence of the boundary drainage on triaxial test results, and the time-lags, due to system flexibility, in measured pore pressures in standpipes and in triaxial tests. He used theoretical analyses to show that a coupled consolidation model, rather than Terzaghi's approach, was necessary to predict the rise in pore pressure in the so-called Cryer problem.

His philosophy was spelled out in a letter written in 1997. He wrote ‘My friend, Professor Balasubramaniam, has correctly pointed out the tension that has developed, and continues to develop, between ‘Theoretical Soil Mechanics' and ‘Practical Soil Mechanics'. This I have predicted over the last 25 years. For those who aspire to the highest levels of Consulting Engineering and who wish to be trained to discharge their duties in the highest echelons: they would be well advised to dig deep in to the pool of theory, and read carefully those accounts of failures, so that their perceptions may be sharpened. The rest is up to them!'Fig. 2 

His combined mathematical and practical approach made him a very effective consultant. He was part of a collaboration between NGI and Kings College on hydraulic fracturing in permeability measurements, a situation that had arisen in the Dead Sea. He was involved from the early days when Golder Hoek set up an office in Maidenhead, England, where he later became Chairman of Golder UK. His projects for Golder included a soil–structure interaction analysis to define remedial measures for settlement of a section of the Elan Valley Aqueduct, founded on soft clay and supplying water to Birmingham and also an involvement in the investigation for the UK's proposed nuclear waste repository. He contributed to the development of offshore artificial sand islands: huge, impermeable bags filled with sand and water, with the pore water pressure reduced by pumping to increase the effective stress and give strength to the sand. During prototype tests in Christchurch Bay, he carried out on-site calculations that allowed him to provide reassurance that the measured pore pressures were consistent with a successful deployment.

Throughout his career, Bob worked with a large number of researchers and consultants, and many of his collaborators have recorded his generosity, his unstinting willingness to help and their debts to him. One colleague has remembered that everything always looked so simple and straightforward when Bob summarised it, and another recognised his ability effortlessly to educate those he worked with through his infectious enthusiasm, which led to long technical discussions. Another, temporarily trapped in a partly collapsed clay inspection pit, remembers Bob's concern, and also his enquiry, after some time had elapsed, about whether he was experiencing creep forces in addition to those that he felt initially! He was inspirational to his students, remaining in touch with many of them until well after his retirement. Recollections span both theoretical and practical situations: a shared enjoyment of tackling the behaviour of a visco-elastic body in terms of effective stress; or Bob remaining philosophically calm and smiling when confronted with a flooded laboratory.

Bob was highly esteemed in the geotechnical community, and was twice editor of Geotechnique, a unique distinction. One of the panel members under his chairmanship remembers being particularly impressed by his leadership of such a varied group of minds. He was the Rankine lecturer in 1974, and presented a paper entitled ‘The analytical method in soil mechanics'. He won various prizes for his papers and his work, including awards by the British Geotechnical Society and the John Booker Medal, and he was elected a Fellow of the Fellowship (now Royal Academy) of Engineering in 1984.

He had a strong sense of enthusiasm for his work and the geotechnical community, a great love for life, music and the company of friends, often accompanied by good wine and good food. Tributes include repeated descriptions of him as ‘an intellectual giant', ‘a true gentleman', ‘an inspiration', ‘a most helpful and friendly colleague', ‘one of the greats in soil mechanics', and, most frequently of all, that he was a very kind man. He died on 23 December 2008, and leaves a daughter, son and grandchildren.