The Opportunities Elastic Waves Offer to Soil Science.

In this poster we describe how soil physical properties can be deduced from the velocity of elastic waves in soil. The poster deals with four issues:

1. Testing published equations for predicting shear wave velocity
2. Deduction of matric potential from shear wave or compression wave speeds
3. Deduction of penetrometer resistance from shear wave or compression wave speeds
4. The non-invasive application of acoustic-seismic coupling measurements

We confirm a previous proposal that the penetrometer resistance was an approximately linear function of the small strain shear modulus, but test the relationship by direct measurement. The relationships are found to have some sensitivity to soil type.  Although estimation of matric potential with either shear or compression wave velocity was found not to be very accurate, the possibility for estimating matric potential from an elastic wave velocity given a priori knowledge of void ratio is an interesting opportunity. We demonstrate the potential of a non-invasive measurement technique for the in situ monitoring of soil physical properties in the field. When soils are regarded as porous and elastic media, sub-surface wave propagation can be indicative of the soil status. Such propagation can be initiated by airborne sound through acoustic-to-seismic (A–S) coupling. Measurements of near-surface sound pressure and acoustically induced soil particle motion can be exploited to estimate the pore-related and elastic properties of soils. Measured data were compared with model predictions based on wave propagation in layered homogeneous isotropic poroelastic media described by linear Biot-Stoll theory. Soil properties were estimated through an optimization process minimizing the differences between the measurements and predictions. The fitted soil characteristics are air permeability, porosity, P-/S-wave speeds (related to bulk and rigidity moduli) and a loss factor. Layer depth was also estimated for multi-layered samples.