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Title: The influence of packing structure on seismic wave velocities in sediments
Author: Schultheiss, P. J.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1982
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Piezo-electric shear wave transducers have been devloped and used in a range of unconsolidated sediments under varying effective stress conditions. A new self-monitoring technique has provided information on transmitter response. Their incorporation in oedometer and triaxial cells, together with compressional wave transducers have enabled the velocity of shear and compressional waves (s and Vp) to be monitored during soil mechanics tests. Installation of these transducers into a variable porosity cell has also enabled the relationship between Vp, Vs and porosity to be defined for sands at low effective stresses. V has been measured in surficial sediments in situ using specially developed probes. In the porosity cell Vs varied between 17 m/s and 120 m/s depending on porosity, grain shape and size distribution. The effective stress-V profile for different sediment types has been defined in the oedometer cell with small decreases in Va occurring after each incremental load for a low permeability clay. Computed static and dynamic moduli exhibit a considerable difference in both magnitude and as a function of stress. This is attributed to differences in drainage conditions. Continuous measurements of s and Vp during cyclic loading tests on sand have clearly defined the behaviour around liquefaction. Vs varied between 0 and 300 m/s in this test and the VpIV ratio enabled the sample liquefaction process to be analysed, concluding that only a small part of the sample had probably failed. In-situ measurements of Vs varied between 27 m/s and 120 m/s without any apparent correlation with electrical formation factor, Vp or sediment type. It has been postulated that the second, slower, bulk compressional wave, predicted by theory but rarely observed might be more appropriate for calculating soil moduli. Observation of received waveforms in the triaxial cell has tentatively identified what may be this slower compressional wave.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available