Effects of Stress History on Failure Behavior of Shallow, Marine Muds from the Northern Gulf of Mexico

摘要

We explore the relation of stress history and failure mechanics of sediments from the Ursa Basin, Gulf of Mexico using directsimple shear experiments. We consolidated specimens to different preconsolidation stresses via load-increment consolidation;then sheared each specimen under undrained conditions to determine shear strength, shear-induced pore pressure, and theirresponses to stress history.The stress history influences sediments properties before failure, and may impact failure dynamics. By shearing sedimentswith different initial porosity or different initial stress, we study how pre-failure conditions influence failure behavior (e.g.,contractional or dilational). This can help us define if failing sediments are prone to contract and accelerate, to creep, or todilate and stop failing.Preliminary results on mud samples from the Ursa Basin indicate that as burial depth increases from 430 to 1340 cm below seafloor (bsf) the cohesion decreases from 18 to 6.5 kPa and internal friction angle increases from 10° to 21°. Thepreconsolidation stress for these specimens ranges from 16 to 42 kPa and experimentally derived peak shear strengths are 30-63 kPa. To investigate stress history, we studied three specimens from 1315-1340 cm bsf that were consolidated to differentmaximum effective vertical stresses or 52, 104, and 208 kPa. The specimens show an increase in shear-induced pore pressuresfrom 38 to 73 to 180 kPa. The normalized undrained shear strengths are 0.29, 0.27, and 0.23 at maximum shear. This indicatesthat the normalized undrained shear strength decreases with vertical consolidation stress, whereas the maximum shear-inducedpore pressure increases with vertical consolidation stress. Together these parameters may influence the depth at which failureoccurs and the post-failure dynamics of these mud-rich sediments, but additional work is needed.All these data are part of the geotechnical characterization of shallow, marine sediments from the northern Gulf of Mexico.These types of data will be used to test and calibrate sediment failure models which are vital for subseafloor geohazardanalyses and offshore infrastructure development. Our study may lead to new assessment techniques of submarine landsliderisks and provide new approaches to mitigate risk.