Assessment of On-Sample Instrumentation for Repeated Load Triaxial Tests

Five laboratories have been involved in a series of comparative studies of the repeated load triaxial testing of soils and unbound granular materials as found in the lower layers of pavement construction. These comparisons with soil, granular materials, and an artificial specimen are outlined. The performance of the varied types of instruments that measure both axial and radial deformations is assessed, with particular attention to the fixing arrangements, instrument limitations, and weight. On the basis of the information presented, recommendations are given about the most appropriate types of instrument. No universal type is recommended, and it is clear that some variation in performance is an inevitable consequence of the measurement process.