A system for measuring local radial strains in triaxial apparatus

The importance of local measurement of small strains is well recognised. Without such measurements, accurate stiffness determination is not possible and can result in overestimations of strains resulting from stress changes in the ground. Axial strain is often considered to be the primary strain to be measured under triaxial conditions and there has been a focus on its measurement. Radial strain is also important, for example for determining Poisson's ratio and bulk modulus, or maintaining K₀ conditions during consolidation. There are a number of devices available that enable its determination, using both direct and indirect measurement approaches. This note describes a system for measuring radial strains directly using linear variable differential transformers. It is shown to be simple, reliable, accurate and robust.