Assessment of anisotropic elastic parameters of saturated clay measured in triaxial apparatus: Appraisal of techniques and derivation procedures

Recent developments in laboratory techniques adopting highly precise local instrumentation have made possible the determination of all five independent elastic parameters necessary for describing the small-strain stiffness in cross-anisotropic soils. However, the techniques and the derivation procedures are not necessarily straightforward, and different processes sometimes lead to apparently inconsistent sets of parameters, revealing their complex and sensitive nature. This paper firstly reports a new fully-instrumented triaxial system that was optimised to test Japanese standard-sized (∅70–75 mm) clay samples. The testing techniques and procedures to obtain the five cross-anisotropic elastic parameters, defined in this paper for recoverable strain smaller than 0.001%, are reviewed. Some updates, including notes on how to deal with creep in soft clays and the optimisation of drained probe rates, are described. A simplified procedure is proposed for completing the parameter determination, without actually measuring the radial displacement, by inverting the relationship between the undrained Young׳s modulus and the drained elastic parameters in saturated soils. The validity of this approach is demonstrated by comparing the parameters of sedimentary clays obtained with and without radial measurements. By eliminating the need for complex radial instrumentation, this approach will make the quantification of stiffness anisotropy more accessible in less-equipped laboratories.