Field Measurements in Soil Mechanics
When I was invited by the British National Committee to give this second Rankine Lecture, I must confess that my reactions were of a mixed nature. While I was naturally very gratified at the honour this invitation conferred on me, I was also conscious of the fact that the task of maintaining the standard expected in these lectures was not an easy one and would be a considerable strain on my capacities. However, I was fortified into accepting the honour by the remembrance of the many occasions in the past when this Society had shown great indulgence to honest if somewhat pedestrian endeavour.
On this occasion, I thought it would be of value to review the position in one broad aspect of the subject, to see how far we have travelled, what remains to be done, and in which direction we should go in future development. Such an exercise could usefully be carried out on many aspects of soil mechanics (all of them important), but the one I have chosen for this talk is that of field measurements on full-scale structures and its role in the application of soil mechanics to civil engineering problems. I have made this choice for various reasons; first, because I think it is appropriate to a Rankine Lecture, for, although in soil mechanics we tend to regard Rankine as a theorist there is no doubt that he had a full appreciation of practical considerations and the difficulties of applying theory to soil problems. In his Manual of Civil Engineering, Rankine wrote: “The properties of earth with respect to adhesion and friction are so variable, that the engineer should never trust to tables or to information obtained from books to guide him in designing earthworks, when he has it in his power to obtain the necessary data either by observation of existing earthworks in the same stratum or by experiment.” Later in the same section he wrote: “There is a mathematical theory of the combined action of friction and adhesion in earth; but for want of precise experimental data, its practical utility is doubtful.” If we interpret the term “precise experimental data” to include reliable field measurements on actual structures, then my theme is obviously in line with Rankine's thinking. My second reason is that the subject is of considerable importance in its own right for the future development of soil mechanics, and anyone who has made a study of Terzaghi's writings will have been struck by his insistence on the urgent need for taking reliable field observations. My third reason is that my colleagues and I at the Building Research Station have been particularly interested in this aspect of soil mechanics and have, from time to time over the past 25 years, carried out a number of investigations involving field measurements of various types on full-scale structures.