Laboratory instrumentation has been developed for sensitive measurement of local lateral-strain of soil specimens. It incorporates a non-contact type of transducer (proximity transducer) whereby lateral deformation of rectangular and circular specimens can be measured in a direct manner at some positions over the central portions, which are relatively free from end restraints. The working principle is described, together with the accuracy and sources of error involved in the measurement. It has been demonstrated in some pilot tests (i.e., drained monotonic loading tests in plane strain compression and a drained cyclic triaxial test) performed on silver Leighton Buzzard and Toyoura sands, that full instrumentation for the local strain measurements, coupled with a previously developed device for the local axial-strain measurement, permitted a continuous examination into the shear-strain-level dependent Young's modulus and Poisson's ratio over a wide range of the pre-failure strain in the orders between 0.0001% and 10%. The scope of the pre-failure strain included the examinations of both the elastic response at extremely small strains less than about 0.002% and the peak strength of a single specimen. It was found that the Poisson's ratio with the shear strain being less than about 0.05% remained more or less constant at around 0.22 and 0.15 for sliver Leighton Buzzard and Toyoura sands, which comprize round and angular to sub-angular grains, respectively. Furthermore, in a broad sense, Rowe's stress-dilatancy relation was found to be valid over the whole range of the pre-failure strain examined, and it was scarcely influenced by the history of over-consolidation at small strains.
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