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Off the ground

Arthur Penman looks back at the developments in soil mechanics that led to the formation in 1949 of the British Geotechnical Society, or more correctly the British Section of the International Society for Soil Mechanics & Foundation Engineering.

The beginning

A major problem for civil engineers has always been the ground. It has often been said that once a structure has been built high enough to be clear of the ground, the remaining construction is straightforward.

Military fortifications needed retaining walls and it was difficult to make them completely stable. Coulomb, son of a distinguished family, entered the military profession as an engineer. After service in Martinique and North America, he became permanently stationed near Paris and was able to devote himself to scientific studies.

Among these was a study of the retaining wall, leading to his famous theory of earth pressure, published in 1776. In examples he gave, the cohesion was taken as zero, 'as is the case for newly deposited earth'. According to Golder (1948), Rankine also recommended that cohesion should be taken as zero.

The publication of Coulomb's work could be regarded as the beginning of our understanding of the behaviour of soil. Terzaghi has said that at the beginning of the 20th century, when the scope and magnitude of construction started to increase at an unprecedented rate, the hazards increased proportionately, and the weakness of the traditional methods of estimating earth pressure and bearing capacity could no longer be ignored. Between 1910 and 1915 attempts were made to establish more reliable procedures independently and almost simultaneously in various parts of Europe and in US.

Terzaghi's Erdbaumechanik auf bodenphysikalischer Grundlage brought together a great deal of the material relating to foundations, pressures on retaining walls and stability of earth slopes under one cover, to be classed as one subject. Interest grew until it was decided that an international society should be set up for the subject.

As we all now know, it was called the International Society for Soil Mechanics, and because those dealing with foundations felt they were being left out,

they insisted on adding the

words Foundation Engineering, producing the unpronounceable ISSMFE.

The first international conference of this society was held in Harvard during 1936, when it was agreed that conferences would be held every four years, and that the next one would be in the Netherlands.

Three quarters of a century ago

In Britain, the subject obtained government support and a laboratory at the Department of Scientific & Industrial Research's Building Research Station, at Garston, near Watford in Hertfordshire.

Southampton Docks was experiencing problems with dock walls and cleverly the British Association for the Advancement of Science was invited to hold its annual meeting there in 1925 when the question was raised about the design of retaining walls.

As a result, the British Association set up an Earth Pressure Committee, chaired by the chief engineer for the docks, FE Wentworth-Shields. An invitation to Oxford professor of engineering science CF Jenkin to look into the problem was accepted with enthusiasm.

Starting from first principles, Jenkin had boxes made with a glass side and a movable end, into which he placed dry sand, poured with coloured marker layers. Release of the end wall in various ways, such as rotating about the bottom or top, or moving out bodily, caused the dry sand to fail in different ways, as shown by the shear planes revealed by displacements of the coloured layers.

Various attempts were made to measure the forces on the end wall, and it was concluded after a great number of experiments had been carried out, that sand does not behave in the manner assumed by Rankine and that its 'angle of friction' depended enormously on the closeness of packing.

Jenkin soon decided that he needed better facilities and to be away from the constant demands of his students. Explaining this to the director of BRS, Dr Stradling, he asked if he could come to the Building Research Station to continue his research. He was given the stout, brick-built stable block of the mansion for his experimental work.

Jenkin resigned his chair at Oxford in June 1929, two years before his statutory date for retirement, and his apparatus was transferred to BRS. That summer he visited the Berlin Hydraulics Research Laboratory, where he was shown methods of measuring the physical properties of soils and so was introduced to some of the developments in this new subject that were occurring on the Continent.

He soon recognised that the real practical problems did not lie with dry sand, but with wet clay. He therefore began a programme of studying the strength and deformation properties of saturated kaolin, consolidating samples that he tested in laboratory equipment he designed and had made in the BRS workshops.

All were advanced for their time and included a triaxial compression apparatus, which he called a conjugate pressure apparatus, spring loaded with a brass cylinder (Fig 1), to retain the cell pressure. Strain in the sample and spring extension were found with electrical contacts.

A point that concerned Jenkin was the strength at zero normal load, and to determine this he devised the ring shear apparatus (Fig 2), with counterbalanced top ring, so that a sample could be sheared without any normal load being applied across the shear plane. This unique apparatus was autographic, using a pointer on a smoked glass plate to record torque and resulting rotational strain.

Unfortunately, no means was devised to measure pore pressures or suction, so he measured apparent cohesion. The argument about the value to assign to c has continued to rage. The latest ideas have been discussed by Schofield (1998) in a learned paper given at the scientific jubilee of Pierre Habib in Paris on 19 May, and a short article in the August issue of Ground Engineering.

Among the staff who had joined BRS was, in 1927, LF Cooling, a physics graduate from Birmingham University. He worked in the brick and stone section, studying the problem of Whitehall coping stones.

Cooling measured the pore sizes of the various stones by using a suction plate apparatus. The porous suction plate was of uniform pore size, with pores small enough so that when once saturated, the curvature and surface tension of the water/air meniscus at the surface of the plate could withstand a pressure differential of almost an atmosphere. A variable suction could be applied to the under surface of the plate by a mercury column, and saturated spec-

imens of coping stone were placed on the suction plate at various suctions.

Increasing suctions drew water from ever smaller pores in the stone, and by weighing before and after, the amount of water sucked from the sample could be measured for each applied suction, thereby revealing the distribution of pore sizes of the specimen.

Jenkin suffered from the cold and tried to keep warm by putting his legs in a hay box under his desk. During 1933 he suffered heart problems and decided that he must retire. His assistants, Bevan and Smith were joined by Cooling: his knowledge of pore sizes and pore suctions had considerable relevance to soil behaviour, although no attempts appear to have been made to measure pore pressures at that stage.

According to Cooling, Jenkin left the laboratory saying he was going home to die. He certainly retired, but in fact did not die until 1940, aged 74, having led a gentle life of retirement in St Albans.

Cooling became head of the research work and in September 1933 the unit was given the distinction of being made into a Section, with the name, taken from the agricultural science, of Soil Physics (it will also be recalled that Cooling was a physicist). The new Section began a programme of research on behalf of the Road Research Board which had been formed in April 1933.

1st international conference of the ISSMFE

Cooling was the only person from England to attend the 1st International Conference on Soil Mechanics & Foundation Engineering at Harvard in 1936. He had submitted two papers, with Smith as co-author. To quote from the BR annual report: 'The conference served to emphasise that soil research is being actively pursued in many countries and that although there is still considerable leeway to be made up on the fundamental side, already the appreciation of the knowledge derived from soil research has proved of value in engineering practice.

'The published volumes containing the papers of the conference provide an invaluable resume of the work being done and also give an encouraging indication of the possibilities and promise of soil science in relation to engineering construction.'

During discussion at the conference, Cooling asked the telling question: 'Is the shear strength at zero normal load of practical value, and if so, how is it used?' Quoting Terzaghi, he said that different results can be obtained by altering the conditions which control the escape of water. We have tried to measure cohesion, he said, using the ring shear apparatus under zero normal load, and have found variation with sample water content.

AW Skempton, a civil engineering graduate from Imperial College, had joined the concrete section of BRS in 1936, and in January 1937 transferred to soils. That year DB Smith was replaced by HQ Golder, recruited from another DSIR Station, Forest Products.

In the laboratory, the soil testing apparatus of Jenkin had been supplemented by shear boxes and oedometers made by workshops, following European designs. A 6cm square shear box had both the normal load and the shear force applied with weights. With this method the rate of strain varied during the test, and post failure conditions could not be measured. A constant rate of strain modification was made by Golder (1942).

A new portable unconfined compression apparatus (UCA) was developed from the earlier Jenkin's apparatus. It took the spring loading and coned end pieces concept from the conjugate pressure apparatus, and modified the smoked glass plate autographic arrangement to the form of a pencil, drawing on a paper chart. The apparatus was described by Cooling and Golder (1940) (Fig 3). Extension of the spring caused upward movement of the chart. Compression of the sample, by lever magnification, moved the pencil across the chart. A celluloid mask of equal stress lines was used to find the maximum compressive stress from the load/deflection curve that had been drawn by the pencil.

The soils group at BRS came even more powerfully to the notice of the civil engineering profession through the failure of Chingford dam.

The Metropolitan Water Board design team had built several reservoirs on the relatively flat land adjoining the Thames and Lea rivers, by the construction of encircling dams.

A contract had been let to Mowlem for a dam adjacent to the existing 8m high King George V reservoir when failure occurred during construction in 1937. MWB chief engineer Davidson (later Sir), who served on the BRS Board, sought advice, resulting in an investigation by the Soil Mechanics Section. Controversy arose between MWB and Mowlem about who was to blame, and Wynne-Edwards (later Sir Robert), agent on the site, asked Cooling for help in finding an independent expert.

Cooling suggested Terzaghi, who was then living in Paris, and Wynne- Edwards took one of the early Imperial Airways scheduled flights from Croydon to Le Bourget. Mike Kilkenny (1986) has recorded remarks made by Casagrande:

'After Austria's Anschluss in the spring of 1938, Terzaghi and his family settled temporarily in France because he was still connected with various projects in French North Africa. There he received a telegram asking whether he would be willing to act as adviser in connection with difficulties in the construction of an earth dam in England. Terzaghi telephoned London and requested an interview in Paris. A few hours later the engineer in charge of the project entered Terzaghi's temporary office with a serious face. Silently he spread plans, sections and boring records on the table. After Terzaghi had examined these data, the following conversation ensued:

Terzaghi: 'Where is the dam located?'

Wynne-Edwards: 'North of London.'

Terzaghi: 'That dam must have been designed by an enemy of the British nation because it will fail, whereupon your Parliament and Westminster Abbey may be washed into the Thames.'

Wynne-Edwards (now smiling): 'It has failed already. '

Terzaghi: 'What instructions did you get from your boss?'

Wynne-Edwards: 'Show him the plans and watch his face. If he remains calm, take your hat and go. If he looks disturbed, bring him over on the next plane.'

Terzaghi agreed with the BRS analysis of the failure and re-designed the dam, pointing out the need to check the strength of the clay at various points, and Mowlem continued with construction. Glossop was sub-agent to Wynne-Edwards, and found it expedient to set up a small soil mechanics laboratory on the site to take and test samples. This was the very early beginnings of a commercial laboratory, which later became Soil Mechanics.

This success led to an increase in visitors to the laboratories, keen to learn more about this new subject. First were civil engineering department heads of several universities, thinking of including soil mechanics in their degree courses, followed by their lecturers, together with many practising engineers who were given short courses at the laboratories.

In 1939 the 49th James Forrest Lecture at the Institution of Civil Engineers was delivered by Terzaghi with the title, 'Soil mechanics - a new chapter in engineering science'. This excellent lecture increased still further the general interest in the subject.

After the declaration of war on 3 September 1939, and in order to maintain contact with practising engineers, BRS organised a soil mechanics discussion group that held its first meeting at ICE on 12 April 1940. This meeting was chaired by Wentworth-Shields, attracting an audience of 40 to hear a paper by Cooling on soil mechanics and its application to engineering problems. Further meetings were held in May, June, July, and January 1941, but after that, meetings were forbidden in London because of risk from enemy bombing.

In 1942 Golder wished to join Mowlem to help form Soil Mechanics, but during wartime, he was not free to leave his post at BRS without a suitable replacement. He placed an advertisement in The Times, which was read by WH Ward, then working on the construction of a munitions factory in Wales, with the result that Ward came to join the soils group at BRS.

During the war, the soils group became involved in over 70 practical investigations including quay walls, flood protection works, large factory buildings, etc. One of these problems was the failure of Muirhead dam during construction in 1941. By the time the war ended, the position of soil mechanics had become firmly established.

During June 1945, a series of four lectures entitled 'The principles and application of soil mechanics' was given at the Institution of Civil Engineers by Cooling, Skempton, Glossop and Markwick of RRL. Non-members of the Institution were admitted on payment of 2s.6d (12p) for a single lecture, or 10/- (50p) for the series.

To support his lecture, Cooling wanted a display of some of the soil testing apparatus from the laboratory. In those days BRS had three vans, the best of which was three litre, six cylinder Dodge, and in this the equipment was transport to the Institution in Great George Street. Once unloaded and taken to the lecture theatre (now named the Telford Theatre), it was found the weight hanger from the shear box has been left behind. I decided that we must have it, so at nearly 4.30pm went off with Sammy Samuels as passenger, got to BRS at Watford, picked up the hanger, and was back to the Institution comfortably before the start of the lecture at 5.30pm. I left the van parked round the corner in Storeys Gate. Such a journey and such parking are now quite unthinkable!

In 1946, Ward went with Golder, Glossop and McLean of RRL on a mission to liberated Europe to find out what soil mechanics developments had taken place in the various countries during the war years. Visits were made to Paris, Lausanne, Zurich, Delft, Ghent and Liege. This extensive tour sowed the seeds for Geotechnique. The possibility of producing a soil mechanics journal was discussed with Daxelhofer at his home near Lausanne, and it was he who suggested the title.

On their return, Golder and Glossop, with backing from Mowlem, set about producing this proposed new journal. To enable the publication to be the journal of a learned society, the Geotechnical Society was formed by Glossop, Golder, Cooling, Skempton and Ward. The subscription was 1 per annum, payable to the Geotechnical Society, a society of convenience, not to be confused with the Soil Mechanics Discussion Group that had held meetings in the Institution of Civil Engineers, during 1940-41.

In 1947, Cooling and Meyerhof, who had joined the Section in 1946, went to North America on a similar mission to renew contacts and to find out what soil mechanics developments had taken place in Canada and US. DSIR's counterpart in Canada, the National Research Council of Canada, had also set up a Building Research Station in Ottawa in 1947.

When the director Legget heard of Cooling and Meyerhof's visit, he arranged a conference on soil mechanics, and this has since been referred to as the 1st annual Canadian conference on SM&FE. Hughie Sutherland, who was studying at Harvard at the time, attended the conference.

A special Golden Jubilee conference was arranged for 1997; Professor Meyerhof, now living in Nova Scotia, and Professor Sutherland from Glasgow University, were among the six who had attended the 1st Conference, and were given special recognition as the 'survivors'. Each of them spoke briefly at the conference banquet to sounds of applause.

Cooling and Skempton put a proposal to the council of the ICE that a British National Committee should be established in preparation for the forthcoming 2nd international conference to be held in the Netherlands in 1948, which had been postponed because of the war. At a meeting in March 1947, council agreed to this proposal and the new committee held its first meeting in April, when it considered arrangements needed to get in papers for the conference.

2nd international conference

The British National Committee submitted 72 papers, almost 20% of all the papers to the conference in Rotterdam from 21-26 June 1948. Some 74 British delegates attended the conference: very different from Cooling as our only representative at the Harvard Conference. The Soils Section at BRS contributed 10 papers: and 15 papers by Golder and Skempton who had recently left the Section, were to be included.

During the conference, a special meeting was arranged, inviting representatives from 23 nations, and one of the items of business was to propose setting up national societies or sections of the International Society.

Back at home, the British National Committee recommended to the Institution council that a British Section of the International Society of Soil Mechanics and Foundation Engineering should be formed under the control of a British National Committee.

On 31 January 1949, the British National Committee held a meeting to establish the British Section of the International Society. Draft statutes were agreed and membership applications were invited. The entrance fee was to be 2 (now the equivalent of about 60), with a annual subscription of 10/-, and an AGM to be held in October. Secretarial work was to be carried out by the staff of the Institution. It is the 50th anniversary of this event on 31 January that we are now celebrating.

Postscript

In 1962, Dr L Muller formed the International Society for Rock Mechanics, and requested national bodies in member countries. To avoid having another national body on this allied subject (when is soil a rock and vice versa), the British Section of ISSMFE under the chairmanship of Professor Bishop, changed its name to the British Geotechnical Society so as to become the national body for both societies.

In 1974, under my chairmanship, we celebrated the 25th anniversary of our national body with papers by Cooling, Skempton, Glossop and Golder. These appear in Geotechnique, vol 25, no 4.

In 1997, during the 14th Congress of ISSMFE in Hamburg, it was proposed to change the name of the International Society. I had great hopes that we were to see the end of the unpronounceable ISSMFE, but no: the change is to ISSMGE, ie geotechnical engineering instead of foundation engineering!

References

Cooling LF and Golder HQ (1940). A portable apparatus for compression tests on clay soils. Engineering, vol 149, no 3862, pp 57-58.

Golder HQ (1942). An apparatus for measuring the shear strength of soils. Engineering, vol 153, pp 501-3.

Golder HQ (1948). Coulomb and earth pressure. Geotechnique, vol 1, no 1, pp 66-71.

Kilkenny WM (1986). The failure and reinstatement of Chingford reservoir embankment. A study of K Terzaghi's first professional assignment in the United Kingdom. Note prepared in the Terzaghi Library, NGI, Oslo.

Schofield AN (1998). The Mohr-Coulomb error. Mechanique et Geotechnique, to be published by Balkema (in press).

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