The application of Biot's theory to sea-bed sediments
Biot's theory - which explains how sediments respond to stresses - has been applied to different sea-bed sediments. To successfully use Biot's theory as a predictive tool, sensitivity studies showed the following experimental measurements are required: the frame bulk modulus. the shear modulus, the tortuosity, the permeability and the porosity. These properties were determined for turbidite sediments from the North Atlantic Ocean (Site 1). and carbonates from the Western Indian Ocean -. (Site 2). The following experimental observations " were made: the permeability varies over 7 orders of magnitude for turbidites from Site 1 due to technique dependent and intrinsic reasons; in-situ shear moduli are 4 times greater than values determined from samples in the laboratory; shear modulus results from resonant column and bender element transducer techniques agree well: experiments designed for obtaining the frame bulk modulus are problematic, and it is difficult to determine pore size / geometry parameters apart from the tortuosity. Biot's theory was used to predict the response of sea-bed sediments to hydrodynamic and ultrasonic stresses. A new low frequency hydrodynamic boundary-value solution was developed from Biot's theory, allowing predictions of tidally-induced pore-pressures. Comparisons between predictions and in-situ measurements at Site 1 were favourable, verifying Biot's theory at low frequencies. At ultrasonic frequencies, Biot predictions of the velocity and attenuation of fast and slow compressional waves were compared to experimental measurements. The slow wave was argued to be induced at free-flow boundaries. and was found to be very difficult to detect in soft water-saturated sediments. A qualitative agreement was shown between Biot fast wave attenuation predictions and new experimental attenuation measurements on a bar of sandstone. For Sites 1 and 2, Biot predictions for the increases in the fast wave velocity for high porosity - permeability sediments agreed with experimental measurements. Elsewhere in the literature, this behaviour has been linked to an increase of the frame bulk modulus with increases in porosity. Alternatively, it was argued such increases in fast wave velocity can be attributed to Biot's dispersion mechanism. and hence are a verification of his theory at high frequencies.