Effect of rheological properties on debris-flow intensity and deposition in large scale flume experiment

Abstract

Debris flows are one of the most serious hazards in the mountainous areas. To assess and mitigate the debris-flow hazard, debris-flow intensities and deposition on fans must be estimated. Rheological properties including yield stress and viscosity are major parameters to describe and predict behaviors of debris flow. In the present study, the effect of rheological properties on debris-flow intensities and deposition on fans of natural clay was investigated using large scale flume experiments. The experimental device employed in the tests consists of a tilting flume with an inclination 17°, on which a steel tank with a removable gate was installed. A final horizontal plane works as the deposition area. Natural soil samples of different water contents were tested. Rheological properties of soil mixtures were obtained from vane-rheometer tests. Non-linear regression analysis was used to assess the effect of yield stress and viscosity on debris-flow velocity, runout distance, deposited area and deposited volume. We found that the relationship between surface velocity profile and horizontal distance was complicated and could be expressed by sixth order polynomial function. Mean velocity, runout distance, deposited area decreased following a power law with an increase in yield stress and viscosity. Empirical equations were proposed to estimate these properties. The results of laboratory tests compared reasonably well with the results from numerical analysis. The results indicated that yield stress and viscosity play a significant role in the behavior of debris flow.