Degree

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

Document Type

Dissertation

Abstract

The occurrence of shallow submarine mass failures in the absence of hurricane activity could be attributed to winter storm passage, creep-like motion of sediment, rapid sediment deposition from Mississippi River flooding events, and excess pore-pressures from biogenic gas production, among other processes. This dissertation aims to fill critical knowledge gaps hypothesized to be related to underlying physical processes accompanying the evolution of sub-decadal landslides on the Mississippi River Delta Front. An expansive database of engineering properties is assimilated and presented for use in determining if laboratory-measured values are reasonable. This database also provides a baseline of delta front geotechnical and geological relationships to compare with future conditions as the delta enters the stage of deltaic regression excacerbated by anthropogenic engineering of the Mississippi River system. A modified settling column using timelapse photography is coupled with a constant strain rate consolidation cell to monitor the engineering behavior of sediments across a range of stresses from initial deposition to long-term consolidation. The resultant relationships are applied with inverse parametric analysis in the numerical program UNSATCON to better constrain sedimentation rates accounting for consolidation, refine the sediment budget on the Mississippi River Delta Front (MRDF), and are discussed in relation to sub-decadal mass failures. Large-displacement undrained shear strength is quantified across a range of strain rates, those which may be imparted by environmental forcings from sub-decadal up to major hurricane scale, to investigate the long-term evolution of slope stability in MRDF sediments before, during, and after failure. The quantified geotechnical relationships are compared with geophysical data to better identify and explain the timing of sub-decadal mass failures detected in sediment cores obtained from the MRDF in 2017.

Date

11-3-2021

Committee Chair

Jafari, Navid H.

Available for download on Monday, October 30, 2028

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