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Title: The velocity and attenuation of broadband acoustic signals in water-saturated sediments
Author: Evans, R. J.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1979
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Laboratory and in situ studies have been made of compressional wave sound velocity and attenuation in water-saturated non-cohesive sediments. A broadband acoustic system (25 kHz to 450 kHz) has been developed for laboratory use. Using this arrangement, information relating to sound velocity, attenuation, and the frequency dependence of attenuation has been obtained from sand sized sedimentary material (with mean sizes ranging from 0.09 mm to 1.33 mm), at various stages of sediment compaction. Particle shape and size distribution statistics have been determined for the sediment samples used in the investigation. Statistical analysis of the data has shown that sample porosity and sediment mean grain size are the sedimentological variables most significantly related to the sound velocity. Attenuation has been shown to be predominantly related to sediment grain size, sample porosity, and overall grain surface area. The frequency (f) dependence of attenuation (a) has been shown to vary in the equation, a = Kfn with n ranging from less than 0.5 to better than 1.0. This variation in the frequency exponent is discussed with respect to the sedimentological characteristics of the samples. The development of an acoustic system for use in the field is described; this has enabled in situ measurements of sound velocity and attenuation to be carried out in medium and fine grained beach sands (over the frequency range 15 kHz to 70 kHz). The results obtained from the field study are compared with empirically derived predictions, based on the analysis of the laboratory data. Finally, the interrelationships between the sedimentological and acoustic characteristics of the sediment samples are incorporated into prediction equations, using the acoustic parameters as independent variables. This approach has demonstrated, for material in the sand size range, the potential of improved delineation of sediment type using compressional wave data obtained in the field.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available