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BIOGRAPHICAL MEMOIRS

Edward Hughesdon Davis 1920-1981

Introduction Road pavement behaviour and design Application of plasticity theory to soil and rock stability problems Application of elasticity theory to soil and rock deformation problems Theory of consolidation of clay soils Application of theory to practical problems

By J.W. Roderick

This memoir was originally published in Historical Records of Australian Science, vol.5, no.3, 1982.

Introduction

Professor Davis died suddenly at his home in Sydney, Australia on 26th February 1981, and his untimely death deprived the geotechnical community in this country of one of its most eminent members.

Davis was born at Hendon in England on 16th December 1920. He gained his early education at University College School in London where he was a scholarship holder for the whole of his tenure. In 1938 he entered University College of the University of London and obtained his degree in civil engineering with first class honours in 1940.

On leaving university he was fortunate in gaining experience in the design and supervision of civil engineering works, first with the well known organization of Sir Alexander Gibb and Partners and then with the distinguished consultant Dr Oscar Faber. But after a few valuable years spent in this way, Davis joined the Royal Engineers in 1942 and then served in the Army for almost five years, first as a lieutenant and then as a captain in the United Kingdom and later in Italy. At the end of the war he remained with the occupation forces in Italy and late in 1946 was demobilised with the substantive rank of major in the Army Education Corps.

Thereafter, like so many others, he had to set about building a new career appropriate to peace-time conditions. Attracted more by research and investigation than by the practice of civil engineering, his first move was to the Road Research Laboratory in England as a senior scientific officer; in 1950 he was appointed to a lectureship at his old college and in 1952 he came to Australia to take up a senior lectureship at the University of Sydney where soil mechanics was to be his main responsibility. Even at that stage it was clear that Davis, following upon his initiation at the Road Research Laboratory, was greatly drawn to soil mechanics as a most promising area in which to work. It was to become for him a dedication and a compensation for all the difficulties of Australian universities associated with limited funds in that period; and an encouragement to set about, quietly and effectively, the task of getting research going after the immediate post-war concentration on teaching.

From the outset of this new interest, Davis saw clearly the needs of the subject. He had come upon soil mechanics in the early 1950's in its emerging stages as a body of knowledge largely made up of art and empiricism driven forward by the practical requirements of foundation engineering. He saw the need to co-ordinate this knowledge and to give it a sound scientific basis. His personal efforts were for many years directed towards the development of a unified theory of foundations and to extending the theory of plasticity to soil and rock stability problems. Both these topics were significantly advanced by his work. But it was in the total task of building up a research and teaching activity in geomechanics – that Davis was so outstandingly successful.

In the ten years after his appointment to Sydney, Davis' work environment greatly improved and he was able to make good progress towards his various objectives. By the end of 1963, the whole of the Civil Engineering Department had been housed in new buildings with excellent facilities for soil mechanics as planned by Davis and his group. The staff he was to gather around him was equally dedicated; later two of them, J.R. Booker and H.G. Poulos, had the distinction of becoming readers early in their careers; and it is gratifying to record that the latter has now succeeded to the chair formerly occupied by Davis.

Also in 1963, Davis was appointed Associate Professor of Soil Mechanics; making full use of the new facilities, there followed five years of very productive activity for the group culminating very appropriately in the appointment of Davis to a new chair of Civil Engineering (Soil Mechanics) at Sydney. In the next ten years the work of the group was again vigorously pursued and Davis found time to become involved in the affairs of the profession and to undertake certain consulting commitments. In 1979 after the retirement of Professor Roderick, Davis was appointed Challis Professor and Head of the School of Civil Engineering, the position he held at the time of his death.

Davis was the author and co-author of two books, four chapters in other books and fifty-five technical papers. They can best be classified into the following five broad categories:

• road pavement behaviour and design
• application of plasticity theory to soil and rock stability problems
• application of elasticity theory to soil and rock deformation problems
• theory of consolidation of clay soils
• application of theory to practical problems.

In all cases his broad philosophy was to apply soundly based theoretical methods to the analysis of geotechnical problems, and to observe the primary characteristics of behaviour and thus define the parameters which influenced this behaviour. His use of simplified models of soil behaviour in no way implied a naive belief that real soil and rocks behave in such a simple and well defined fashion. Rather it reflected his desire to avoid the frustrations of trying to quantify all the many non-ideal characteristics of real materials, to develop solutions which could be used for design purposes and in which the geotechnical parameters – albeit simplified – had a physical meaning. The wide use of his solutions in practice has justified his approach and many of the charts which he and his colleagues developed are now reproduced in standard textbooks.

Road pavement behaviour and design

This topic was the earliest which engaged Davis' attention, and he continued to be interested in it throughout his career. His early papers were concerned largely with practical methods of pavement design but later, he attempted to obtain a closer understanding of the structural behaviour of road pavements through the results of a model pavement constructed at the University of Sydney. Davis' papers were widely consulted by road engineers in the 1950s.

Application of plasticity theory to soil and rock stability problems

Davis will perhaps best be remembered for his contributions in this area. While studying problems involving the stability of soil masses, he became convinced that further progress would only be possible if a more rigorous approach, based on the theory of plasticity, were adopted. He grappled with the problem of applying the theory of plasticity to the assessment of soil stability and to the problem of understanding the relevance and significance of traditional engineering approaches in relation to the more rigorous theory. In doing so, he developed a unique understanding of the subject and his work clarified the concepts of many other people attempting to apply plasticity theory to soil mechanics.

He applied limit state theorems to cohesive soils and investigated their validity for other classes of materials. He recognised the shortcomings of the associated flow rule and developed a tractable model with a non-associated flow rule; this proved to be a major advance in the more realistic modelling of plastic soil behaviour. The results have found wide application in practice. Subsequently, a wide variety of problems were considered and solutions obtained for the bearing capacity and stability of homogeneous and non-homogeneous soil masses and slopes.

In later years Davis and his research students linked together the theories of elasticity, plasticity and consolidation and explored the complete load-deformation behaviour of foundations. One of his major interests at the time of his death, was the accurate prediction of collapse loads for foundations and soil masses using both load path and bounding techniques. But Davis, always watchful of the engineering significance of his research, was reluctant to publish his theoretical ideas before their implications had been fully explored and understood; consequently some of his work relating to plasticity theory, has not yet appeared.

Application of elasticity theory to soil and rock deformation problems

It was by the more extensive use of the theory of elasticity that Davis was able to produce more rational solutions to deformation problems which hitherto had been treated by largely empirical methods. Here again he was at pains to emphasise that progress and understanding would only come if a consistent, theoretically sound and simplified model of soil behaviour, were used as the basic concept. Accordingly, in his early papers he made use of classical elasticity solutions as a basis for the treatment of more complex problems by a technique which was the forerunner of the boundary element method.

His use of elastic theory for settlement prediction, though initially received with scepticism by some, eventually formed the basis for a unified method of settlement analysis, applicable to pads, piles and raft foundations. These methods are now widely used in practice. But it should be pointed out that his acceptance of elastic theory as a basis for settlement analysis did not mean that he was unaware of the potential shortcomings of this simple model as a representation of real soil. He continually emphasised the need to use elastic theory with due caution and with parameters which were determined over an appropriate stress range. His philosophy was therefore similar to that of Professor Lambe of M.I.T. who was, at about the same time, developing the stress path method of deformation analysis.

In his later work Davis extended consideration of deformation problems into the post yield phase making use of the elastic-plastic model of soil behaviour, so enabling a study to be made of load-deformation behaviour right up to failure. Among the problems treated were anchor plates, shallow foundations and pile foundations.

Theory of consolidation of clay soils

Professor Davis was also deeply interested in the problem of predicting rate of settlement. He continually sought to improve the theory of consolidation and moved away from a consideration of the simple one dimensional case to obtain important fundamental solutions to problems in two and three dimensions. He was quick to realise the significance of incorporating non-linear effects and produced several valuable and elegant solutions.

His early work on this subject was concentrated on the non-linear consolidation characteristics of soils under one-dimensional compression. He later extended his work to three dimensional problems and the charts he developed with Poulos are now widely used for rate of settlement predictions for shallow foundations. In subsequent developments, the effect of soil yield and finite strain were investigated.

Application of theory to practical problem

Although his interests were largely academic, Davis was acutely aware of the needs of geo-technical engineers to have convenient and reliable means of analysis for use in practical situations. Several of his papers dealt with the application of theories of various degrees of sophistication to field problems and the assessment of the applicability of the theory by comparing theoretical predictions with measured performance. For example, in a paper with H.G. Poulos published in  Aust. Geomech. J.  in 1975, it is demonstrated how judicious use of relatively simple analyses could provide predictions of behaviour almost as good as those from much more refined methods. In the same paper he was also able to emphasise the importance of proper interpretation of the soil data to select design parameters. On this point mention should be made of the Prediction Exercise conducted at M.I.T. to forecast the performance of a pile in a bridge abutment tested in 1973 and that of a highway embankment loaded in 1974. In both cases Davis and his collaborators assessed the available geotechnical data and used their theoretical techniques to predict performance prior to the results being revealed. For both the pile and the embankment the predictions proved to be very satisfactory, reflecting not only the applicability of the theory, but also the quality of the judgement associated with the selection of the soil parameters.

These very substantial contributions to geomechanics by Davis have been widely recognised in a number of ways. His colleagues and friends were particularly pleased when in 1980 his work in theoretical soil mechanics was honoured in two ways. He was elected a Fellow of the Australian Academy of Science and was awarded the inaugural John Jaeger Memorial Medal by the Australian Geomechanics Society. At the Third Australia-New Zealand Geomechanics Conference in Wellington, New Zealand, at which the medal was awarded, he delivered what was to be his final major lecture on the subject of plasticity solutions relevant to the bearing capacity of rock and fissured clay. This lecture described some of his recent work which he felt bridged the gap between soil and rock mechanics, and was enthusiastically received. With characteristic modesty, Davis publically attributed his award to the co-operative efforts of his research group.

One of Davis' great attributes was his ability to stimulate and encourage his research students and colleagues. He urged students to undertake broad areas of research and not to confine their attention to a small aspect of a problem, and in so doing, helped them gain an overall appreciation of the subject. He was never too busy to view the latest findings of an enthusiastic research student or colleague and would willingly put aside his administrative tasks to discuss and critically appraise the proferred results. His ability to detect flaws in philosophical or theoretical arguments saved others from embarrassment on more than one occasion.

It is evident from his papers covering this category that Davis had the gift of clear engineering insight; whatever his particular theoretical pursuit, he never lost sight of possible practical applications. He was always able to hold the attention of a profession which increasingly sought his advice in the understanding of complex geomechanics problems encountered in the design and construction of major projects carried out in many parts of Australia. These included the foundations of major buildings in Canberra, the Botany Bay container terminal, the Kingsford Smith Airport terminal building, the Liddell power station, the foundations for the Ranger uranium treatment plant and the foundations for an oil-drilling platform off the northwest coast of Australia. Other professional links included a period of study leave in 1968 spent with Soil Mechanics Limited in England; and a formal association of more recent years with a firm of foundation engineers in this country who especially valued his technical advice and his ability to see a problem in the total broad spectrum.

From the beginning of his association with the profession Davis saw the need for academics, practising engineers, geologists and others to have their own forum for developing their common interest in geomechanics. Undoubtedly the eventual formation of the Australian Geomechanics Society owed much to Davis' patient efforts. Ten years earlier, he had been the major force in establishing the Sydney Soil Mechanics Group, which met on a quite informal basis to discuss matters of practical and theoretical interest. His activities in this direction also extended into the international field through his involvement in the affairs of the International Society of Soil Mechanics and Foundation Engineering. He played a significant part in this society and was the Australian vice-president for the period 1969-73.

Davis also took an active part in University affairs; colleagues who worked with him and were fellow members of committees invariably found his counsel wise and moderate. When the Mining Engineering Department at Sydney was without a permanent head, he willingly undertook the chairmanship of the Faculty Board for this course; he was soon on good terms with the students and able from his own background to update the teaching and give new direction to the course. In 1979 when he was appointed Head of the School of Civil Engineering at Sydney, he set out in a most enthusiastic manner to co-ordinate new programmes for a large staff with diverse teaching and research commitments. His quiet diplomacy and effective planning enabled him to achieve much in the short time before his death.

Davis' influence extended well beyond the boundaries of this country and when on sabbatical leave he was always a good ambassador for Australian geomechanics. He spent three periods of study leave in the United Kingdom and the United States including in particular working commitments at Massachusetts Institute of Technology, Cambridge University and the Universities of Manchester and Swansea. As time was to prove, the early visits were the beginning of a valuable interchange between the group at Sydney and that at M.I.T.; a similar relationship was also developed with the soil mechanics group at Cambridge where Davis was in 1978 an Overseas Fellow of Churchill College.

Davis and his charming wife were excellent hosts and took great pleasure in entertaining their friends and especially visiting academics. For many years their major relaxation was to set off with their three children on camping holidays to explore the lesser known but very attractive parts of Australia. They were most knowledgeable about the countryside and always enjoyed showing overseas visitors something of the beauties of their adopted city and country.

Of the man himself, the views of his colleagues have been well expressed in the following words: Ted Davis will be remembered as a kind and civilised man concerned for his family and his students, as a distinguished practitioner and contributor to the art and science of geomechanics, but above all, one who insisted on the highest standards of intellectual rigour in the academic study of engineering subjects. His many colleagues and students who have learned from him, will provide a continuing memorial to his work.

He is survived by his wife, two sons and a daughter.

The author wishes to acknowledge helpful discussions with Mrs Davis to whom the sympathy of the Academy is extended; and information provided by former colleagues Dr Booker and Professor Poulos. The author is also indebted to the latter for kindly reading and commenting on the manuscript.