The Velocity of Shear Waves In Unsaturated Soil.

The velocities of shear waves V_s in two soils, a sandy loam and a silty loam, were measured at various matric potentials and confining pressures. We used a combination of Haines apparatus, pressure plate apparatus and a Bishop and Wesley tri-axial cell to obtain a range of saturation and consolidation states.  We proposed a single effective stress variable based on a modification to Bishop’s equation which could be used in a published empirical model (Santamarina et al., 2001) to relate shear wave velocity to soil physical conditions. Net stress required a nonlinear transformation. Matric potential was converted into suction stress with the function proposed by Khallili and Khabbaz (1998), thus requiring an estimate of the air entry potential. We found it was possible to fit V_s to void ratio, net stress and matric potential with a set of four fitted parameters which were common to all soils at various states of saturation and consolidation.  In addition to the data collected in this study we also used previously published data (Whalley et al., 2011). The utility of shear wave measurements to deduce soil physical properties is discussed.

 Khallili, N., Khabbaz, M.H.  1998. A unique relationship for χ for the dteremination of the shear strength of unsaturated soils. Geotechnique 48, 681-687.

Santamarina, J.C., Klein, K.A.  Fan, M.A. 2001. Soils and Waves. Wilely &Sons, Chichester, England.

Whalley, W.R., Jenkins, M. and Attenborough K. (2011) The velocity of shear waves in saturated soil. Soil Science Society of America Journal. 75:1652–1657