Phil. Trans. R. Soc. Lond. A. 274 , 421-428 (1973) [ 421 ] Printed in Great Britain The use of ground strain measurements in civil engineering B y W. H. W ard and J. B. B urland Building Research Station, Garston, Watford, WD 2 7 JR Strains of the ground are of increasing importance in civil engineering for as projects get larger the strains they induce often exceed the natural strains. For the engineer to ensure the safety and stability of a structure and its surroundings he must be able to predict and, if need be, control the strains. Our approach is to measure the deformations in specific cases and to use the information to gain a better understanding of ground behaviour, to determine parameters of the ground to use in prediction and to check the safety and design of the project. It demands simple and sensitive instruments that can be used reliably under rigorous field conditions. Examples of recent studies are given. I ntroduction To ensure the safety and stability of civil engineering projects such as dams, excavations and large buildings the engineer needs to be able to predict, and if necessary, control the local ground strains, in particular those caused by the new construction itself, for they may be quite large and arise generally whenever the surface topography is altered, or from mining, from the loading of the project, or from changing the ‘ climate ’ near or in the ground. Our approach is to measure the deformations of the structure and the local ground in specific cases and to use the information: (a) to gain a better understanding of ground behaviour; to determine para- meters for future predictions by the detailed analyses possible with a computer; as a check on the design and safety of the project. The traditional method of ground investigation and design relies heavily on laboratory tests carried out on small cores to determine the ground parameters and the use of rather simple theoretical models of ground behaviour to predict strain. This approach has severe limitations. For example, the core tests are not representative of a large ground mass, and simple theoretical models neglect substantial inhomogeneity and anisotropy of the ground. Our method is illustrated here by means of a few examples of ground deformation measure- ments associated with constructional loading and excavation, the interpretation of the measure- ments and their use for prediction. E quipment , accuracy and duration of measurement We need in our method simple, reliable and sensitive measuring equipment for wide use under rigorous field conditions. Normal optical surveying methods are not always sufficiently accurate, and use has been made of the Mekometer (Froome 1971) and precise water levels. Reference is made to some specific equipment in the examples that follow. The local displacements caused by the civil engineering project should be measured with respect to the most stable reference marks in undisturbed ground and an accuracy of better than 1 mm is often necessary. Natural displacements, especially hydrologic and temperature effects, need to be known or avoided in selecting reference points. Strains must often be measured to 10-6 and even 10~7 over distances varying from tens of millimetres to tens of metres; tilts are measured to 10-7 radians over tens of metres. 27 Vol. 274. A. Downloaded from https://royalsocietypublishing.org/ on 16 January 2022