The framework of anisotropic elasticity has been used to develop relationships between various anisotropic stiffness parameters found in the literature. It is shown that they are functions of the two Young's moduli and two Poisson's ratios that describe a cross-anisotropic soil, but not of the independent shear modulus. Multiple drained triaxial stress path excursions have been performed on 100 mm dia. samples of natural Gault Clay from Madingley in a stress path cell. Anisotropic parameters at small strains along different stress paths are reported and compared. It is shown that there are some advantages in performing tests at constant vertical and constant horizontal effective stress. Horizontally mounted bender elements on the same trixial samples have enabled the two anisotropic elastic shear moduli to be measured. Combining results from both sets of tests has enabled all five independent cross-anisotropic elastic parameters to be estimated. The Gault Clay at Madingley is highly anisotropic, although the degree of anisotropy depends on the way it is defined.

The inclusion of anisotropic stiffness parameters in sophisticated constitutive models necessitates their determination in the field and laboratory. Hitherto, anisotropy of small-strain stiffness of clays has occasionally been examined in the laboratory by measurements on specimens sampled at different orientations. The authors have developed a device to propagate and receive horizontal shear waves with both vertical and horizontal polarization through 100 mm triaxial samples. The device incorporates bender elements embedded in the pads of a horizontal belt. In tests on both reconstituted and natural samples of Gault Clay, each of the transmission velocities Vs(xh), Vs(hx) and Fs(hh) has been measured during stress path tests. The ratio G0(hh)/G0(vh) has been shown to be highly dependent on stress state. Laboratory data on natural samples show results broadly consistent with in situ results. Pour pouvoir inclure des paramètres de rigidité anisotrope dans des modèles constitutifs perfectionnés, il faut les déterminer sur le terrain et en laboratoire. Jusqu'à présent, on a parfois examiné l'anisotropie de la rigidité d'argiles aux petites contraintes en mesurant des échantillons prélevés à diverses orientations. Les auteurs ont mis au point un dispositif qui permet la propagation et la réception d'ondes de cisaillement horizontals avec polarisation verticale et horizontal dans des échantillons de compression triaxiale de 100mm. Le dispositif comprend des elements de flexion noyés dans les plaquettes d'une bande horizontal. Dans des essais de parcours de contrainte sur des échantillons reconstitués et naturels d'argile de Gault, on a mesuré les vitesses de transmission Vs(vh), Vs(hv) et Vs(hh). On a montré que le rapport G0(hh)/G0(vh) depend en grande partie de l'etat de contrainte. Les résultats obtenus en laboratoire sur des échantillons naturels concordent assez bien avec les résultats obtenus sur le terrain.

A conventional direct shear apparatus (DSA) has been modified to improve its articulation by moving the point of shear load application to the sample centre. Jewell's symmetrical arrangement has been adopted for a 100 mm square shearbox, resulting in increased dilation rate and reduced rotation. Testing using coarse Leighton Buzzard sand has enabled the performance of the modified DSA to be optimised by exploring different test configurations. Optimum results were obtained with a substantial initial gap between the shearbox frames of 5D 50 , the use of thin rubber edging strips to contain the sand, and the omission of grid plates at the sample boundaries. Upper-frame rotations persist during testing, but have almost no effect on measured parameters. A framework of relationships between parameters measured in a direct shear test ((ö9 ds ) p , ł p and (ö9 ds ) ld ) and relevant plane strain parameters ((ö9 ps ) p and ö9 crit ) is set out, based on Rowe's flow rule and Davis's (1968) relation. Stroud's simple shear apparatus (SSA) data for coarse Leighton Buzzard sand have been examined and shown to fit Rowe's flow rule. The output from the modified DSA also fits these relationships well, and shows good internal consistency. A simple relationship enables modified DSA peak direct shear friction angles to be converted into plane strain friction angles. Large displacement direct shear friction angles for the modified DSA are related to critical state friction angles by tan(ö9 ds ) ld sin ö9 crit .

Sand-steel interface tests have been performed using a modified direct shear apparatus that enables accurate dilation measurements to be taken. Average roughness and maximum roughness, when divided by D50, are equally good at correlating both friction and dilation data. Below a certain relative roughness threshold, interface behaviour is non-dilatant. Above that threshold, interfaces show classical stress-dilatancy behaviour, with peak values following a simple flow rule. When peak interface friction and dilation angles are normalised by dividing by equivalent direct shear values, dilatant interface test data covering a range of particle sizes, relative densities and surface roughnesses fit a simple linear model when plotted against relative roughness on a logarithmic scale. When relative roughness reaches an upper limit, interface behaviour becomes fully rough, reproducing peak friction and dilation angles in direct shear. Normalised peak interface friction ratios are likely to range between 0.5 and 1.0 for sand on rolled steel surfaces, with the value depending primarily on particle size.

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