Repeated triaxial loading of soil: apparatus and preliminary results

A repeated load, triaxial test apparatus has been developed to provide information on the dynamic and long term behaviour of soil subgrades. A servo-controlled, electro-hydraulic system is used to generate continuous and transient stresses. The transient deviator and all-round confining stresses can be synchronised to test soil types whose mechanical properties are critically dependent on the presence of a confining stress. 'On-sample' techniques based on electro-optical and capacitance transducers have been developed to make accurate measurements of small soil deformations. Weak soils can be tested as the attachments are light and do not apply contact pressures to the soil. The performance of the apparatus is demonstrated by an investigation of the dynamic behaviour of an undrained, highly compressible clay specimen. Dynamic Young's modulus was found to decrease markedly with deviator stress but not to vary significantly with mean normal stress. Dynamic Poisson's ratio was approximately 0.5, increasing slightly with deviator stress but not varying significantly with mean normal stress. (A)