Geotechnical Characterization of Mississippi River Delta Front Sediments-Paper

Paper

Pdf Summary

The Mississippi River Delta Front (MRDF) is vulnerable to submarine landslides that threaten offshore infrastructure and can release hydrocarbons. This study characterizes the geotechnical behavior of recently deposited sediments near Southwest Pass to support improved slope-stability and geohazard assessments.<br /><br />Researchers tested cores collected from three settings: prodelta, mudflow gully, and mudflow lobe. Laboratory work included low-stress torsional ring-shear tests to measure drained strength, unconsolidated-undrained triaxial tests, and photogrammetric settling-column experiments to track sediment settling and self-weight consolidation. Pore pressures were also monitored during settling and changes in water level.<br /><br />Photogrammetry captured the transition from zone settling to compression over roughly two days. Once consolidated, the sediments transmitted changes in applied water pressure almost completely: the pore-pressure response corresponded to a Skempton coefficient of about 0.95. This indicates that added loading is initially borne largely by pore water, consistent with the sediments’ high saturation and limited consolidation.<br /><br />For prodelta sediment, the measured fully softened drained strength was 6.5 kPa at an effective normal stress of 12 kPa. Drained strengths agreed well with empirical relationships developed for subaerial clays and silts. Undrained strengths were slightly lower than drained strengths. Among the three settings, prodelta sediment showed the highest undrained strength, gully sediment was intermediate, and the chaotic debris of the mudflow lobe had the lowest strength.<br /><br />The results provide a comparative assessment of sediment resistance to mass movement under low-stress conditions. The authors emphasize that undrained behavior is especially important for MRDF slope stability and recommend developing an undrained, large-displacement ring-shear method to better represent failure conditions.

Keywords

Mississippi River Delta Front

submarine landslides

geotechnical behavior

slope stability

pore pressure

drained strength

undrained strength

ring-shear tests

self-weight consolidation

mudflow sediments