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that conference may still remember the spirit of enthusiasm which prevailed, because each of the participants felt that he was witnessing an historical event. This event replaced the groping of a fcw individuals by an international, organised action and induced some of the most gifted members of the profession of civil engineering to join the smali group of pioneers in their effort to establish a rational basis for earth-work engineering. It is fascinating to review the subseąuent developments.

« As our knowledge of the complex physical properties of soils increased we also became morę and morę aware of the limitations which naturę has imposed on our capacity to predict the performance of our slructures on a purely theor-etical basis. This insight turned into a powerful incentive for reliable observations in the field, during and after construction. As a consequence the increase of our knowledge was accom-panied by a rapid growth of our accumulation of reliable observational data. Thus we are approaching an ideał State in which we can use our theoretical knowledge to fuli ad-vantage without the risk of being occasionally misled by it.

« Every few years we have met again to record our progress, and each of these meetings was for me a memorable occasion, because it gave me an opportunity to share the joy of dis-covery of those who had new and singificant findings to report. This is the first Conference I cannot attend. I have no reason to complain because I never expected to last for ever, and I have reached the mellow age at which one submits without resentment to the Stern dictates of the physicians. However my thoughts are with you. I do hope that this conference will be as constructive as its predecessors, and I do not doubt that our French colleagues, assisted by the inexhaustible resources of gay Paris, will do their best to keep you happy between the meetings.

Very best greetings to all of you from your absentee Honorary President. ”

In reply, I shall send a telegram, saying :

“ The Paris Conference has just started with every sign of success, but we shall miss you terribly. Everyone joins me in sending greetings and best wishes. ”

Terzaghi guided the affairs of this Society for 21 years. We owe an incalculable debt of gratitude to him, for the scientific contributions he has madę, without which soil mechanics as we known it today could hardly exist. A pro-found and highly original research man, and an outstanding consulting engineer, he possesses the analytical ability, the creative power and human understanding which are the prerequisites of true greatness.

It is with some satisfaction therefore that I can mention the recent publication of a book devoted to Terzaghi and his work, which will reveal to posterity at least some of these qualities which we who have known him so greatly admire.

France

Our meetings are being held in this very fine building; itself the result of a most successful collaboration between architects, engineers and artists of several nations. No morę fitting location could be imagined, and I would like to ex-press our deepest thanks to the Director General of UNESCO, M. Veronese and to M. Montagnć, for placing such excellent facilities at our disposal. On all previous occasions we have been fortunate in the ambience of these Conferences, but this time a standard is being set which can hardly be surpassed.

If I had been allowed to select the country for this Conference I would have chosen France without the slightest hesitation. For it is to France that we owe the foundations of modern civil engineering, and it was to the celebrated Academy of Sciences in Paris that Coulomb gave his epoch-making paper of 1773 which marks with precision and with great distinction the origin of soil mechanics. And it was another French engineer, Alexandre Collin, who was perhaps the first to realise the supreme importance of field studies.

In morę recent times, we have had many important contributions, especially by Resal and Caquot. Also, M. Caquot held the preeminent position of President of the Academy of Sciences in 1952, and in this way he has conferred a notable honour on our subject. We are delighted that he is with us today as President of the French Organizing Committee and I wish to thank him for the very kind remarks he has madę.

I need hardly remind you that the French have always displayed a bold and imaginative grasp of the possibilities of new methods and materials. The outstanding example in the 20th century is, of course, their superb design work in reinforced and pre-stressed concrete. But the same attributes have been displayed in the development of alluvial grouting, and it is largely due to engineers such as M. Mayer and M. Ischy that this new and important technique has been brought to the stage where it can be successfully employed in conditions which hitherto would have presented almost unsurmountable difficulties. For instance, it is doubtful if the great Serre Ponęon dam, which is underlain by 100 metres of river sands and gravels, would have been constructed at all, had it not been possible to grout the alluvial deposits throught this immense depth.

For all these reasons I am particularly happy that we should be meeting in France and paying tribute to the engineers of this country.

The past 25 years

As Prof. Terzaghi has mentioned it is exactly a quarter of a century sińce the first International Conference was held, in 1936, at Harvard University. That Conference was organised by Prof. Casagrande as an act of faith; for it was far from certain that many people would attend. In fact, the most optimistic expectations were exceeded and 200 engineers took part. At the time of the 4th Conference, however, in 1957, the membership of our Society had increased morę than tenfold. Since then it has nearly doubled again and now totals 4,700.

Apart from this remarkable increase in the number of engineers actively engaged in soil mechanics, what are the outstanding achievements during the past 25 years? Taking a broad view, two things stand out with clarity. Firstly, it is now proved beyond all doubt that the engineering behaviour of soils in practice can be analysed in a rational manner. In 1936 we believed that this might be the case, but it was not an established fact; to illustrate the point I would mention the shear strength of clays and the stability of clay slopes.

When the Harvard Conference was held the pioneer work on shear strength had just been completed, but a great deal of work was still necessary, especially in the field, before anything like a complete and reliable picture could be ob-tained; or even before we could be surę that this was not an almost hopeless ideał. We have not reached finality yet, by any means, but it is now possible to approach many of the problems with reasonable confidence. And this success has been largely achieved by the insistent and Iogical appli-cation of the principle of effective stress : Terzaghi’s greatest discovery and the very corner stone of modern soil mechanics. This requires the measurement of porę pressures during shear. Such measurements are now madę almost as a matter of course, but years of patient work were required to develop satisfac-tory methods, especially for clays; and in this connection we

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