Field Measurements in Soil Mechanics

Abstract

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.

Contributions to Géotechnique 1948–2008: Tunnelling

“…This clearly reflects the importance of field observations both to control the works and understand mechanisms of behaviour for future projects. It seems appropriate to start by referring to the Second Rankine Lecture, given by Cooling (1962), concerning 'Field measurements in soil mechanics'. He drew attention to the fact that, in lined tunnel construction and operation, small movements can have large importance.…”

“…'Ground support for tunnels in weak rocks' was the title of Ward's Rankine Lecture in 1978. His name is associated with many extensive tunnel monitoring projects undertaken by the BRS (as mentioned by Cooling, 1962), and this paper covered one aspect of his work. It did not seek to define how to design supports for tunnels in weak rocks, but drew attention to the many factors that influence support loading and convergence, and how they operate.…”

“…The first of the papers involving tunnels in London Clay concerns the Bakerloo line tunnels mentioned 26 years earlier by Cooling (1962). Burford (1988) gave an update of their response, showing excellent long-term monitoring data that clearly indicate that the tunnels were continuing to heave (by up to about 50 mm) with little decrease in the rate of movement 27 years after the excavation above them was made.…”

The engineering behaviour of fill materials: the use, misuse and disuse of case histories

“…The importance of making field measurements was also recognised by Leonard Cooling (1945) of the Building Research Station, which later became the Building Research Establishment (BRE), when speaking at the Institution of Civil Engineers in June of that year:…”

“…In his Rankine Lecture, Cooling (1962) again stressed the importance of field measurements. As a diagnosis of what was needed and a recommendation of the direction that geotechnical engineering should take, the comments of Terzaghi and Cooling showed great insight, but when Terzaghi added a word of prophecy to the effect that 'the centre of gravity of research has shifted from the study and the laboratory into the construction camp where it will remain', he proved to be overly optimistic.…”