Small strain stiffness of carbonate Kenya Sand: Fid-Bau Portal

Small strain stiffness of carbonate Kenya Sand

Fioravante, V. / Giretti, D. / Jamiolkowski, M.

Abstract In this paper results of a series of tests performed in a large calibration chamber (CC), consisting in the propagation of seismic shear and compression waves in dry carbonate oolitic sand from Kenya, are presented and analysed. The tests were aimed at assessing how the state parameters affect the small strain shear and constrained moduli. The tested sand was characterised by the determination of the index properties, its mineralogy and grain crushing, the latter investigated by oedometer tests. The calibration chamber houses a cylindrical specimen 1.2m diameter and 1.5m high. Within the specimens, reconstituted by dry pluviation at relative densities of 30% and 85%, were embedded arrays of three miniaturised geophones, used alternatively as source and receiver of seismic body waves. Shear and compression waves were propagated along the vertical, horizontal and inclined planes. By assuming a cross-anisotropic medium with a vertical axis of symmetry, the seismic tests allowed the assessment of the elastic parameters. The effects of the fabric, of the stress induced anisotropy as well as the stress history on the velocity of propagated seismic body waves are quantified and described in details. Semi-empirical correlations are calibrated; they can be used in engineering practice to analyse body wave velocity profiles measured in situ and to evaluate the state parameters and anisotropy properties of carbonate sand deposits.

Highlights • Dry pluviated carbonate Kenya Sand behaves as a cross-anisotropic material. • The effect of stress induced anisotropy depends on the stress ratio. • The velocity of body waves is influenced by overconsolidation or pre-stressing. • Calibration chamber (CC) tests allowed evaluation of 5 independent elastic constant. • CC and Tx test results allowed the calibration of a semi-empiric correlation.