A simple gauge for local small strain measurements in the laboratory

A simple device named a "local deformation transducer"(LDT) was developed to investigate soil stiffness that can be measured in the laboratory for strain levels ranging from 10 to the minus 6 power to 10 to the minus 2 power. First, a theoretical consideration of the nonlinear, but uniquely determined, relation between strain gauge (output voltage) and axial strain is described. The accuracy of the strain measurement using the LDT is then discussed based on the theory and the results of calibration tests. The stability of the output voltage was examined for a few days using a dummy. In isotropic consolidation tests performed on a fine clean sand in triaxial cells, the internal axial strains measured using the LDT were compared with those associated with no bedding error, extrapolated from the results of tests using specimens with various heights. The capability of the LDT was demonstrated in triaxial tests in which the variations of Young's modulus of a gravel, a cement-treated sandy soil, and a soft rock were measured for the prescribed range of strains as the specimens were subjected to both monotonic and cyclic loadings.