Experimental and Theoretical Studies of Near-Bottom Sediments to Determine Geoacoustic and Geotechnical Properties

Abstract : In a program designed to develop methods for predicting and measuring certain geoacoustic and geotechnical properties of the sediments immediately beneath the sea floor, several new tools were developed to measure in situ properties such as undrained shear strength, shear wave velocity and angle of internal friction. These tools include a motorized penetrometer designed to measure quasi static cone penetration resistance up to depths of two meters into the bottom, a Love wave source and linear receiving array to measure shear wave velocity, and a 22-caliber source and array designed to generate Scholte waves with higher dominant frequency than conventional airgun sources. Using data obtained with this equipment as well as from other CBBL investigators, dynamic shear moduli derived from measurements of shear wave velocity were correlated with cone penetration resistance and the results were found to be consistent with results obtained by geotechnical engineers for many different clay soils. This result suggests that their regression equation may also be used for marine sediments of the type tested in the current program. In addition to the above work, the Biot-Stoll model was used to establish a baseline geoacoustic model for the soft, gassy soils of Eckernfoerde Bay which constitutes the starting point for studies of the perturbing effects of free gas bubbles and other scatterers in the sediment.