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Alec Skempton 1914-2001

OBITUARY

One of the greatest civil engineers of the 20th century, Professor Sir Alec Skempton, died on 9 August aged 87.

He played a key role in the development of the science of soil mechanics and geotechnical engineering through his research and teaching and was an inspiration to generations of geotechnical engineers. Here John Burland, Ralph Peck and Arthur Penman give some personal memories of the man and his work.

Arthur Penman

There was something of a depression in 1936, so when Alec Skempton graduated in civil engineering from Imperial College, he was pleased to get a position in the concrete section of the Building Research Station (BRS), not too far north of central London.

He soon saw where the activity was and the following year transferred to the soil physics section. Its head, Leonard Cooling, had just returned from the first International Conference on Soil Mechanics & Foundation Engineering, in nice time for the section's investigation of the failure of Chingford Dam in the Lea Valley.

He made an important contribution with a calculation based on Terzaghi and Frohlich (1936) of the rate of gain of strength that would develop under the weight of the dam in the soft clay layer through which failure had occurred: a calculation made when he was only 24 and included in the paper by Cooling and Golder (1942).

Controversy between owner and contractor led to Karl Terzaghi being brought from Paris. On site and at BRS he met Skempton and they became lifelong friends.

In 1940 there was trouble during construction with Muirhead Dam on the Rye Water. The senior partner of the consultant described it not as a failure but as 'a wee movement' Skempton and Hugh Golder found the dam within 5. 1m of full height. After placing pegs on the major section, a further 0. 5m of fill was placed and the resulting slip reactivation was measured with the pegs, revealing the position of the circular slip surface.

The first half of the dam had been built in the traditional manner with little or no compaction.

Then, to complete construction for wartime requirements, diesel powered track laying machinery had been introduced, as at Chingford, speeding up construction considerably. Skempton showed that lack of time and drainage had limited the development of strength in the lower fill. In this case the solution was to complete the dam with its crest 5m lower than original design.

The same consultant was responsible for the neighbouring Knockendon Dam which at that time was at about one fifth of its full height. Skempton suggested measuring the pore pressures in the fill with drive-in standpipe piezometers made from 75mm steel pipe, fitted with a pointed shoe and perforated with 6mm holes over the bottom length of 30-45cm. This was probably the first use of piezometers in a British dam.

Soil mechanics was a very new subject and the Chingford analysis aroused considerable interest from the civil engineering profession. Universities began looking into the possibilities of teaching the subject and Skempton gave several courses of lectures: he was an excellent educator.

Professor Fisher Cassie from the University of Newcastle was one of those who had come to BRS to learn something of the subject, and I had the good fortune to be one of his undergraduates. He had some of the laboratory apparatus and taught us the basics, then he managed to persuade Skempton to give four lectures with practical sessions for we students and the engineers of the Newcastle district.

Skempton's enthusiasm made me very interested in soil mechanics and later the university was offered two places at BRS with the result that I joined the soils group on the last day of July 1944.

I became Skempton's assistant, finding the effect of the use of logarithm spirals for the shape of failure surfaces behind retaining walls and making laboratory tests on various samples from, among other places, Rosyth.

After Chingford, BRS had offered to help the Metropolitan Water Board with any problems it might have with any of its new dams. This led to batches of U4 samples from the foundation for Walton Reservoir arriving at BRS for triaxial testing.

Ours was a very small group and we had to ask for help. Alan Bishop, who had recently joined the water board upon graduating from Cambridge, was sent to assist.

The King George V reservoir had been refilled after wartime safety drawdown and was found to leak excessively. Alan Bishop and I made an investigation, and while we were writing this up in Skempton's room one evening we suddenly realised that the last 321 bus to Watford had gone.

Alan had a bike and I was living in the BRS lodge, but Skem was in a bit of a fix: but I knew how to get out one of the BRS vans, so we carried on working. On the drive to his flat in Watford, in darkness lit only by masked headlights, we came across a police checkpoint.

I thought we might be in difficulties, but Skem, who was a big man, puffed out his chest and said in his very authoritative voice that we were on important government business, in something of a hurry and would the policeman please mind standing to one side. Fortunately for me, on the way back the checkpoint had gone.

When Skempton went to Imperial College [in 1946] he took Bishop with him, where they formed an outstanding teaching team, introducing the diploma course in soil mechanics, attracting the best students from around the world, and expanding with the best additional lecturers.

The second ICSMFE, held in Rotterdam in 1948, gave an additional fillip to developments: Britain provided 57 of the published papers, of which Skempton wrote seven.

The first of the postwar embankment dams, Usk and Daer, were designed by Binnie, Deacon & Gourley, who were quick to engage Skempton as soil mechanics consultant.

The partner responsible for the Usk Dam in Wales knew about Chingford and when a layer of silt was revealed by excavation for the stilling basin and found to lie under the whole area for the downstream shoulder at a depth of about 3m, he came to BRS for advice about the rate of consolidation of the layer and to question the need for its removal.

Following the methods proposed by Barron (1948), I designed a layout of bored sand drains that would accelerate consolidation sufficiently, and offered to design and install remote reading hydraulic piezometers to check on developed pore pressures during dam construction. These pressures in the silt layer under the dam remained remarkably low throughout construction.

But the second set of piezometers that I installed in the fill recorded dangerously high pore pressures, and to obtain a second opinion, Skempton was brought in. Thus began a close connection with Skempton during the construction of both dams, measuring construction pore pressures in the fill. In the case of Usk, Skempton proposed the use of drainage layers in the fill to reduce the lengths of drainage paths, thereby speeding up the rate of consolidation.

This was the first installation of drainage layers within the fill of British dams: a method used for many further dams. Skempton and Bishop advised on the design and construction of Chew Stoke Dam that was built on a soft foundation. A pattern of bored sand drains was used to provide drainage for the naturally occurring horizontal features in the soil, and I installed piezometers to check on their effectiveness.

During subsequent years I had close connections with Imperial College, working with Bishop and giving lectures. One of the most memorable joys was lunch with Skempton and some other members of his soils group.

He used to come along to Bishop's room, whistling softly and twiddling a piece of his hair, and say, 'Coming to lunch?'We would then go off, continuing to discuss the current problem and others during the walk across to the refectory, during the lunch and for the walk all the way back.

Laurits Bjerrum, director of the Norwegian Geotechnical Institute, was a frequent visitor and enlarged our discussions with problems from Norway. In 1973 he came to London to introduce Bill Lambe's Rankine Lecture, staying at the Hilton.

When Kevin Nash went to see him on the morning of the lecture, he found that Bjerrum had died. Bill Lambe, who had come with colourful suit and sparkling bow tie, wanted to cancel the lecture, but Skempton stepped into the breach and spoke beautifully about what had happened, concluding that the last thing Bjerrum would have wanted would be for the lecture to be abandoned.

Strength tests with controlled rates of strain revealed the reductions to residual strength that could occur past peak, and the presence of slickensides found in London Clay during tunnelling caused Skempton to think about the effect of shear surfaces occurring naturally in some soils, caused by tectonic movements in the past. His approach can be seen in his study and analysis of the foundation conditions for the Mangla Dam in Pakistan, where his understanding of shear zones saved an otherwise dangerous situation and led to a new, safe design.

To celebrate his 70th birthday [in 1984], he presented a delightful and informative lecture at the Institution of Civil Engineers about residual strength affecting landslides. Subsequently, we found that as he was talking Carsington Dam, then under construction, was failing. He was engaged by the owners, and I was engaged by the loss adjusters, to investigate the failure. We worked together on site for some considerable time and his conclusion was that there were pre-formed slip surfaces, exhibiting residual strengths, in the foundation clay. He said to me, in no uncertain terms, 'This is not just another Chingford. '

To celebrate his 80th birthday, he gave us an absolutely outstanding lecture, reassessing Brunel's tunnel under the Thames, giving previously unknown explanations for the difficulties encountered.

Skempton played a vital role in the development of soil mechanics in Britain, from the first discussion group that held meetings at the ICE in 1940-41 until they were stopped because of air raid restrictions, through to the formation of the British National Committee of the International Society for Soil Mechanics & Foundation Engineering, which became the British Geotechnical Society (now the British Geotechnical Association).

He was instrumental in the formation of Geotechnique, publishing in the first issue an important paper about the properties of postglacial clays that were poorly understood at the time, and very many papers since, including his fourth Rankine Lecture.

He was appointed as vice president of the ISSMFE for the second international conference in Rotterdam in 1948, and Terzaghi handed over the presidency to him during the London Conference in 1957.

After this conference he suggested that surplus funds could be used to establish the Rankine Lecture, to be given on alternate years by an overseas speaker, with cheaper, home speakers in between. When my turn came, as one of the cheaper speakers, I was thrilled and honoured to have been able to persuade Skempton, despite his very intensive work on Carsington, to introduce me. He balked at saying that he influenced my interest in soil mechanics, and instead of saying that Cassie asked him to give a short course, changed it to, 'asked one of the station's staff to give a short course' It gave us extreme pleasure when at last his status was recognised with a knighthood. At Richard Jardine's professorial inaugural lecture at college last year I bumped into Skem, stooped as he was then, two days after his 86th birthday, rushing to have tea, and we had a short chat. He had just come from the investiture at Buckingham Palace.

'Did you have to go down on both knees?' I asked. 'No, only one, ' he replied. 'And did she help you up?''No, you have to manage by yourself. ' So, it's a bit hard to be knighted when you're old! But of course the Queen was only 11 years younger herself.

As Peter Rowe used to say, we are all getting near the end of the plank. Those who have slipped off include Roscoe, Cooling, Bishop, Golder, Ward, Glossop, Rowe and now, the most famous of them all, the truly great Skempton.

John Burland

I first saw Skem at the Fifth International Conference in Paris in 1961. I didn't meet him then, I just worshipped from afar.

I remember two things. First his attempt to speak French, which sounded pretty impressive to me as a philistine colonial returning from South Africa, but which I understand may not quite have been Queen's French!

The second was his presidential address, in which he warned of complacency arising out of our rapidly increasing ability to carry out sophisticated analyses. The classic Treadgold definition of civil engineering is 'The art and science of directing the great forces of nature to the benefit of mankind'.

Skem finished that section of his address with the following profound statement: 'Optimism and overconfidence may impress one's clients, but they have no influence on the great forces of nature. 'There is a sermon in that. I certainly used it to great effect with the Pisa Commission.

Something we all experienced was Skem's incredible memory - his amazing ability to recall information, often gleaned years before. For my PhD I studied Rendulic in some detail - he published his major work in 1937. One day we were discussing his work and I remarked on a detail of his apparatus.

Skem was quiet for a minute and then said: 'John, I think you will find that he did such and such'. I checked, and I had got it wrong; he had remembered correctly.

Another attribute was his extraordinary laser-like concentration. When he focused on a subject, or enthused about it, he used to burn it up, such was the intensity of his single-minded pursuit of it.

In some ways his mind was not quick. He was almost childlike in the way he would keep asking questions - questions which to us sophisticates would seem somewhat naive. Then their profundity would gradually dawn.

Skem needed to assemble and study all the facts for himself and then draw his own conclusions.

His approach is reflected by the words of Thomas Huxley: 'Sit down before the facts as a little child; be prepared to give up every preconceived notion, follow humbly and to whatever abyss nature leads, or you shall learn nothing. '

Because Skem was always prepared to work that way, we have learned so much from him and we will continue to do so. At the end of his professorial inaugural lecture in 1955 - how I wish I had been there - he finished with a quotation from Blake:

'To see the world in a grain of sand, And heaven in a wild flower;

Hold infinity in the palm of your hand, And eternity in an hour. '

He finished with characteristic good humour, saying: 'I trust that the last hour has not seemed like an eternity. '

We had to work very hard on Skem to get him to the celebration for his knighthood - he said he would not come if there were going to be speeches. He hated formal gatherings, but he loved informal ones. I remember how much he enjoyed the MSc start of year party - the students loved meeting him and certainly never forgot the occasion.

At his knighthood celebration there was music of the sort that Skem loved.

There was that splendid song about Brunel's tunnel that Judith [his daughter] sang. I am sure that the occasion brought back fond memories of earlier musical occasions when he played the flute.

Professor Jean Kerisel referred most warmly to the occasion when wrote: 'Fonder of music than of compliments, Sir Alec led me quickly to an auditorium where we were to hear The Thames Tunnel Song with its chorus: 'Hail great Brunel, the tunnel is the wonder of the world just now'. '

He went on: 'Since the middle of the last century, many great achievements of civil geotechnical engineering have sunk into oblivion and it was very stimulating to hear a hundred voices enthusiastically singing a chorus, not deprived from British humour, in honour of a great pioneer' - and I know he was referring to Skem as well as Brunel.

Of course everyone wished that Skem could have gone on and on. He will do so in our hearts.

Ralph Peck

The loss of Alec Skempton closes a chapter in the development of soil mechanics in Britain and indeed the world. The impact of his work is legendary, as illustrated by the merit of the research and the quality of the students who came from all corners of the world.

Geotechnical engineers today may not realise the fundamental nature and scope of Skem's work, may not be aware of his contribution to geological engineering, or may not know of his passion for and expertise in the history of civil engineering and building construction.

In these respects he was a true Renaissance man, not in the sense of a dry scholar, but of boundless enthusiasm.

I first met Skem at the Third International Conference on Soil Mechanics & Foundation Engineering in Zurich in 1953. He promptly invited me to stop in England on my way home. I was happy to do so.

I saw much to admire at Imperial College, but I also learned of Skem's knowledge of and love for medieval cathedrals, especially during a visit to Salisbury Cathedral, which he knew intimately.

We discovered a common interest in old buildings, and later in Chicago, where the skyscraper had its origin, we delved into the basements of many historic structures. His interest was far from superficial. His more recent interest in exactly what the soils were that collapsed into Brunel's Thames tunnel is well known, including his pleasure in holding in his hands the very field notes dealing with the collapse.

His contributions bridged significant gaps between geology and soil mechanics, as witnessed by his paper 'Notes on the compressibility of clays', published in 1944, not in a journal of engineering but in the Quarterly Journal of the Geological Societyof London.

Perhaps most notable for their insight is the series of papers on undrained strength of saturated clays, included in the Proceedings of the Second International Conference in 1948. Today's engineers need no longer be confused about evaluating the undrained shear strength of saturated clays, but the issue was a serious and crucial one at that time. Why did the failure planes in a cylindrical compression test sample not make an angle of 45degrees with the axis of the sample if the angle of internal friction was zero?

Skem presented a whole series of papers on the subject in the proceedings, attacking it from several points of view, not quite arriving at a definite conclusion but illuminating the subject (one that Terzaghi and I skirted in the first edition of Soil Mechanics in Engineering Practice, which appeared in the same year).

Skem's discussions of the controversial issue of why the effective area of contact between particles in a saturated soil seems to be zero contained much insight.

He was not afraid to tackle difficult problems, and solved many.

At the same time, he produced some of the first field data comparing measured behaviour and predictions on footings and on slopes. Out of his slope studies came the illuminating concept of the residual shear strength of clays and shales.

There can be no question that he greatly advanced knowledge through his extensive and careful field studies, always with an eye to the geology. That many of his findings are now taken for granted does not mean they came easily.

Finally, professionally, there are his students. I will not attempt to name them, but they are to be found worldwide, many with disciples of their own. They and all of us are his beneficiaries.

Skem added a flair to our profession. He was a great researcher, teacher and engineer; but above all he was a great human being.

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