Risk assessment from potential submarine landslides typically involves back-analysis of past failures in the area. Input to the process are two key field observations: soil volume evacuated and mapped extent of the debrite. Both observations entail uncertainties and judgement. The runout distance strongly depends on the soil flow characteristics. The paper outlines a systematic approach to understanding and determining flow characteristics of seabed soils through rheology testing done on actual field samples using the Brookfield vane-in-cup-rheometer (ASTM, D2196-05). Step-bystep test procedures developed specifically for characterization of potential debris flows are outlined herein. The efficacy of the approach is demonstrated through back-analysis of a case history involving plastic clays on a steep escarpment. Initial hypothesis from field observations pointed to evacuation of a large volume and an elongated and curved runout. Simulations relying on measured soil characteristics evidenced that the initially mapped runout is more likely a resultant of multiple events, with a distinctive main debrite whose runout is consistent with the debris flow simulation, and a more distal deposit interpreted to result from turbidity surges and post-event sediment reworking.
Arash Zakeri and Benoit Spinewine
Keywords: rheology testing, debris flows, submarine landslides, depth-averaged simulations
Publisher: DFI