Preliminary Investigations of Rheological Properties of Busan Clays and Possible Implications for Debris Flow Modelling

Abstract

AbstractTo investigate the post-failure dynamics of subaerial and subaqueous landslides in various environments, we need a detailed analysis of the geotechnical and rheological behaviour of fine-grained sediments. For fine-grained sediments found in the subaerial and subaqueous environments, rheological research should be conducted as a prelude to understanding flow behaviour and hazard assessment. In this paper, the rheological characteristics of Busan clays from the Nakdong deltaic plain are examined in a shear rate-controlled system. A comparison is made between the Busan clays and low-activity clays in terms of rheometer geometry. Flow curves obtained from the controlled shear rate and the shear stress mode are examined. The viscosity and yield stresses obtained from different geometries, which may produce wall-slip among cylinder, ball-measuring and vane-measuring systems, are highlighted. Based on the relationship between the liquidity index and rheological values (viscosity and yield stress), flow motions are compared. Results show that the differences in mobility are significant when assuming that the flowing materials behave as a Bingham fluid. The runout distance is controlled by the yield stress of fine-grained sediments. Differences in yield stress may be caused by wall roughness and the distance between the ball (vane) and the wall in the rheometer. Under the same geomorphological conditions, the runout distance calculated from vane-measuring systems is much lower than that from ball-measuring and cylinderic systems. These difficulties must be minimized to predict debris flow mobility and to correctly perform hazard risk assessment.KeywordsRheological propertiesBusan claysBall-measuring and vane-measuring rheometerDebris flow mobility