Anisotropic Small Strain Elastic Properties of Sands and Mixture of Sand-clay Measured by Dynamic and Static Methods

Abstract

ABSTRACT A comprehensive series of triaxial compression (TC) tests have been performed on two air-dried poorly graded fine sands (Hostun and Toyoura sands) and on a moist mixture of sand and clay (Hostun sand—Kaolin clay). Tests were conducted by means of two high precision devices: a hollow cylinder apparatus (HCA, “T4C StaDy”) and a triaxial apparatus (TA, “Triaxial StaDy”). The elastic properties of these granular materials were systemically and carefully measured at different stress levels by both static and dynamic methods, i.e., by small cyclic loadings for strain levels below 0.001% and by shear (S) and compression (P) wave propagations using piezoelectric elements. It is found that the elastic properties measured by static and dynamic methods become very consistent if the stress-induced anisotropy is properly taken into account. For this, two different assumptions were considered in the back analysis of the dynamic test interpretation: an isotropic elastic behaviour and a cross-anisotropic (or transverse isotropic) elastic behaviour. The resulting differences in the determination of each of the elastic parameters are quantified and discussed. An hypo-elastic model (DBGS model), taking into account stress-induced anisotropy (including rotation of stress principal axes) is found to be relevant in the prediction of both static and dynamic measurements. This model was otherwise used to consider the cross-anisotropic elastic assumption.