Abstract Submarine landslides occur globally and have the potential to damage seafloor infrastructure and trigger tsunamis. Recently, diatomaceous weak layers have been hypothesized to play a role in triggering submarine landslides on passive continental margins by generating overpressure. Here, we mixed two types of clay, an illite‐rich glaciomarine Boston Blue Clay (BBC) and a smectite‐rich marine clay from Eugene Island (EI) Block 330 offshore Louisiana, each with marine or lacustrine diatoms at mass ratios of 100:00, 90:10, and 80:20 to investigate the consolidated‐undrained shear strength of diatomaceous mudstones. These samples underwent uniaxial consolidation to 950 kPa before undrained shearing. Failure modes vary from bulging failure (BBC mixtures) to distinct failure planes (EI mixtures). Under peak conditions, BBC shows higher shear strength (202 vs. 176 kPa), effective friction angle (32° vs. 24°), and excess pore pressure (500 vs. 360 kPa) than EI, respectively. Adding 20 wt.% marine diatoms increased the peak undrained shear strength (BBC: +47 kPa, EI: +44 kPa) and effective friction angle (BBC: +9°, EI: +10°) similarly in both lithologies. However, excess pore pressure increased more rapidly in EI mixtures (+250 kPa) than in BBC mixtures (+5 kPa). Therefore, EI mixtures are more susceptible to shear failure with increased diatom content than BBC mixtures because of lower shear strengths and friction angles and faster pore‐pressure buildup. When combined with prior hydromechanical data, the findings indicate that diatom contents exceeding 20 wt.% and/or higher sedimentation rates are needed to produce overpressure sufficient to destabilize a passive continental slope.
Scott et al. (Fri,) studied this question.