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Technical Note (National Research Council of Canada. Division of Building Research), 1961-09-01
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The International Soil Mechanics Conference, Paris, July 1961
Legget, R. F.; Crawford, C. B.
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-DIVISION OF BUILDING RESEARCH
NATIONAL RESEARCH COUNCIL OF CANADA
'f
ECIHIN ][CAIL
IV (/)']['IE
No.
346
NOT FOR PUBL.ICATION FOR INTERNAL USE
PREPARED BY R. F. Legget and
C. B. Crawford
CHECKED BY APPROVED BY R.F.!...
PREPARED FOR Soil Mechanics Workers in Canada
DATE Sept. 1961
SUBJECT THE INTERNATIONAL SOIL MECHANICS CONFERENCE,
PARIS, JULY 1961.
The increasing status of soil mechanics in the international field, as a vital part of modern cIvil engineering, was clearly shown by the presence of more than 1100 engineers and scientists from fifty countries at the Fifth International Conf erence on Soil Mechanics and Foundation Engineering. Held in Paris throughout the week of July 17, the meeting was held in the modernistic auditorium of UNESCO, this unique meeting place adding to the international atmosphere. Every major country of the world, from both sides of the iron curtain, was represented; the international amity that pervaded all discussions, public and private, throughout the week was a heartening experience.
Dominant throughout ail the sessions was the increased attention now being given to soil mechanics on construction jobs. This is a matter that has long been stressed by Dr. Karl Terzaghl, Honorary President of the International Society. For the first time since 1936
when these international meetings started, Dr. Terzaghl was unfortunately but unavoidably absent, to very general regret. Dr. A. W. Skempton of Imperial College, London, presided as President. Dr. Arthur Casagrande, of Harvard University, was elected president for the ensuing four
years until the 1965 Conference whIch WIll be held in Montreal, Canada.
In his introductory remarks, President Skempton traced the development of soil mechanics during the past 25 years. He mentioned particularly that in this period the rational method of analysis had been
" 2
-proved in soil mechanics and that the most important development was the widespread acceptance of soil mechanics as a branch of civil
engineering. He cautioned against complacency and the tendency toward handbook engineering in the engineering treatment of soils.
The linking of the results of laboratory studies of soil properties with the actual performance of civil engineering structures was forcefully outlined by W. J. Turnbull, of the U. S. Army's Waterways Experiment Station, Vicksburg, Miss" in his contribution to the concluding panel discussion. He suggested that in modern construction practice, the following steps in the use of geotechnical procedures were essential:
(1) Proper preliminary geological investigations at the building site; (2) Prosecution of well planned subsurface investigations planned on the basis of geQlogical information; (3) Carefully conducted laboratory tests upon good soil samples; (4) Careful application of the results of pre-liminary studies in design; (5) Accurate and thorough control of all con-struction operations involving soil; (6) Development of the necessary instrumentation for observing soil behaviour in the completed structure; and (7) Detailed study of the results of observations upon the completed structure after it has been in service for some time, so that the con-clusions thus obtained' cab. be reported for general information and for application in the design of similar future projects.
It was an indication of the well planned program for the Conference that each of tJ:1ese cardinal points, with the exception of the first, was
prominently featured in one or more of the eight sessions in which the Conference conducted its proceedings. A few speakers mentioned the essential geological background to all field soil mechanics studies and it was suggestecl that this subject should be given more prominence at future conferences, together with rock mechanics, a subject in which some significant aelvances were briefly reported.
Each of the main sessions started with a summary by the general reporter of his written summation of the papers submitted in his assigned field of interest. A panel discussion was then featured, the speakers being selected from a variety of countries and because of their familiarity with the subject under review. Discussion from the floor then followed. The system worked reasonably well, some of the panellists getting intQ quite pointed but constructive argwnents. The size of the meetings, however, militated against a completely free interchange of views. There was much private talk as to how this difficulty can be over-come while yet retaining the benefit of such a world-wide gathering of those expert in the field.
3
-Soviet engineers contributed fruitfully to the discussions. A. Denisov discussed field measurements of pore water pressure; based on his experience, he did not agree with suggestions of A. W. Bishop (U. K.) regarding the inter-relation of laboratory and field measu.rements of this important parameter in soil stability calculations. It was clear that some of the disagreements in discussion were due to differences in the use of standard terms. Decision of the Executive Committee to have an international group work on agreed definitions in soil mechanics was widely welcomed; this follows the successful completion of an inte:::--national glos s ary of terms, to which the actual definitions will be amos t useful supplement. Agreement on over seventy symbols for use 'in
theoretical soil mechanics literature was announced; slowly, an inter-national language in the field is developing.
There was much interest in discussions of slope stability in soils, several tributes being paid to the pioneer work of Alexandre
Collin, whose pioneer volume on this subject was published in Paris in 1846. (A translation into English is available from the University of Toronto Press). A. Trofimenkoff (U.S.S.R.) reported on very deep open cuts in the Soviet Union, to: depths of 200 metres. He described one cut one square kilometer in area, 100 metres deep, excavated to 60 metres below the original water table. Soviet engineers do not agree with the suggestion of observing surface strain on ｾｨ･ face of a soil slope,
as indicative of potential failure, considering that this gives results too late! They regularly observe the ground back of the crests of all big slopes, in this way obtaining usually several weeks warning of failures from the appearance of initial cracking at the tops of the surfaces of failure, always to the rear of the slope crests.
Trofimenkoff also reported on a meeting in the U. S. S. R. in October 1960 at which the subject of loss of cohesion in clay soils was the sole topic, twenty papers on this. one problem being presented. Dr.
Skempton gave a masterly review of current thinking on this matter, indicating that he is quite certain that cohesion does not decrease with time for all clays. He reminded his audience that as early as 1855 Rankine had pointed out that cohesion could not be relied upon in soil stability
calculations. Field evidence is the vital need for better understanding of this critical factor in stability calculations. He cited some British
examples but appealed for more accurate descriptions of well studied cases of failure in which the cohesion factor could be estimated with accuracy. He suggested that weaknesses in clays such as fissuring and other effects of weathering might be responsible for clays exhibiting in the field shear values less than the maxima shown by laboratory tests, pointing out that only in relation to slope stability can this matter be investigated since in foundations: stresses tend to increase rather than to decrease as in cuts.
4
-The importance of climate, and of climatic changes, was also stressed in connection with slope stability. DIAppolonia (U.S.A.) des cribed some of the difficulties experienced in dealing with the shales of West Pennsylvania, suggesting that three processes were at work in changing their character with time - chemical changes, fracturing and fissuring, and subsequent weathering on exposure. An Australian speaker described dams in Western Australia constructed of disinte-grated granite, the character of which was very variable in view of its origin as the result of weathering.
As in previous conferences, the uncertainties involved in the measurement of soil properties held a prominant position. More than 70 papers dealt with testing and the panel discussion ranged over a broad set of problems. Detailed consideration was given to the scatter of test results and it was ･ｾｰｨ｡ｳｩｺ･､ that the source of test errors should be sought rather than handling a large volume of test results on a statistical basis. The question of cementation and structure of clays drew considerable comment. The implications of -deformation under plane strain conditions were discussed both in connection with test measurements and in connection with bearing capacity computations.
The earth pressure session stimulated much pointed discussion. Special attention was given to the uncertainties of applying theoretical
treatment to earth pressure problems and discussion dwelt at length on the influence of strain in the earth mass on computed and measured earth pressures. The difficulty of determining pressure distribution against a retaining wall by theoretical means was discussed. The only actual measurements presented during the discussion were those made at the Norwegian Geotechnical Institute and these results provided evidence of the limitations to a completely theoretical treatment.
Disagreement was evident in the assessment of the shape of footings on their ultimate bearing capacity. Information on swelling and shrinking clays on shallow foundations was presented from various
countries. Studies of this problem seemed to have matured since the London conference although little new information seemed to be available. At the same time negative pore pressures appear to be computed with more confidence.
Discussion of piled foundations ranged from detailed accounts of meticulous French experimentation upon elaborate test piles to des-criptions of field operations in which actual pile load tests failed
com-pletely to agree with anticipated results based on advance tests. R. B. Peck (U. S.'A. ),gave an excellent review of recent North American studies but he had to point out that recent ･ｸｰｾｲｩ･ｮ｣･ｳ with a piling job in North Dakota
5
-failed to agree with the results of a general review of actual bearing strengths of pilefi in
clay w,hich
he had reported to the Highway Research Board. There was therefore, general agre0rtlent with the suggestion of L. Zeevaert (Mexico) that possibly enginee'rs were attempting tosimplify soil mechanics too
much
by not realizing the many complications that affect every pile foundatiofi and which mAke every piling job unique.Among the variety of Iu'bjects disc::uliIlJed at the concluding session were the problems caused by
lQea.
and liilmilAr ｯｰ･ｮＭｴ･ｾｴｵｲ･､ soils.M. Henry (France) described
problem.
encountered especially in sampling such soils in southern France, in connection with power and navigation developments on the Rhone. R. Ha€lieU (Switzerland) suggested that here was one field in which soil mechanics and snow mechanics had close affinity. He referred to Swiss and. Canadian work in considering these two newscientific disciplines in close association and suggested that at future conferences snow mechanics should be included in the program since it has such close relation to soil mechanics.
Canadian participation in the Conference was in keeping with general activity in soil mechanics work throughout Canada. Eleven
Ganadian papers appear in the Proceedings, these havip.g been selected from twenty-four original submissions to the. N. R. C. Associate Committee on Soil Mechanics and Foundation Engineering (which acts as the Canadian National Committee for the International Society). They will be available, as a set, later in the year, in the form of one of the Associate Committee's Technical Memoranda. About thirty Canadians were present in Paris, . some with their wives. Dr. Meyerhof, of Nova Scotia Technical College, acted as General Reporter for Section One of the Conference (on Soil
ｾｲｯｰ･ｲｴｩ･ｳ and their measurement), presenting the spoken summary of his Report in French as a compliment to the French hosts, and in keeping with Canada's bilingual culture which was repeatedly in evidence at the meeting. Dr. H. Q. Golder took part in the panel discussion in Section Two, on Techniques of Field Measurement and Sampling. Mr. R. F. Legget completed his term as Vice-President for North America, being succeeded by Prof. L. Zeevaert of Mexico. Mr. Legget spoke at the closing session, voicing Canadian pleasure at the acceptance of the invitation to hold the 1965 Conference in Canada, and saying that all Ganadian workers in the field would work together to ensure the best possible conference in Montreal.
In the ftnal plenary session, President Skempton paid tribute to the work of the general reporters for their labours in summarizing the great number of papers presented to the Conference, and all published in advance in two large vo1\ul1es. Almost three hundred papers had thus been published. Over seventy of these were on soil properties (and
6
-associated testing), indicating clearly the phenomenal growth of soil laboratory work. All the discussions presented will be published-later in a third supplementary volume. As with previous International Soil Mechanics Conferen<;:es, the set of three volumes will form an invaluable guide to the present state of knowledge in this virile young scientific part of the practice of civil engineering. Sets of the three volumes will be publicly available. They may be ordered, at 350 New French Francs about for the set, from ,Dunod, 92 Rue Bonaparte, Paris 6e.
