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Lee, H.J., 1988

Geotechnical properties of northeast Pacific Ocean sediment and their relation to geologic processes

Bibliographic Reference

Lee, H.J., 1988, Geotechnical properties of northeast Pacific Ocean sediment and their relation to geologic processes: University of California, San Diego, Ph.D. dissertation, 328 p., illust.


Geotechnical engineering approaches can be applied productively to solving problems in marine geology, as shown by three example investigations. In the first, core samples of normally consolidated and overconsolidated sediment from the northeast Pacific basin were tested to determine shear strength and maximum past stress. The results showed hiatuses in the sediment column, representing sediment removal events whose extent could be specified, By comparison with a sedimentation model and by using methods of geotechnical stratigraphy, the timing of the events was estimated to be within the Quaternary, when sea level was lowered past the shelf break during glacial cycles. Resulting enhanced tidal currents, superimposed on steady thermohaline flow, likely exceeded the threshold erosion speed of the sediment and caused sediment resuspension and transport. The second investigation resulted in a method for estimating causes and locations of certain undersea landslides along the northeast Pacific margin. Results of engineering property tests on core samples were synthesized using normalized-parameter techniques and expressed as critical earthquake acceleration factors or wave heights needed to initiate failure. Locations with relatively low values of these process-related parameters were most susceptible to landslides according to four case histories off the coasts of California and Alaska. Seismic loading was the common cause of observed failures. Landslides can mobilize into flows after failure if the steady state shear strength is less than the downslope shear stress. On the continental shelf of southeast Alaska, such a condition occurs when wave loading causes expansion of the sediment fabric but typically does not occur during earthquakes. The third investigation showed that variations of density with calcium carbonate content in calcareous oozes are predictable and dependent upon the physical properties of the non-carbonate material. A model predicts dominance by the carbonate framework or by the non-carbonate matrix depending on which element supports the sediment fabric. Shear strength behavior is explained using the same model although coring disturbance and overburden stress effects must be considered. This model of the variation of density with calcium carbonate content can potentially be applied to remote sensing of submarine stratigraphy.

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