CRITICAL DEBRIS FLOW ANALYSIS PARAMETERS - YIELD STRENGTH AND VISCOSITY

Two properties that are commonly used in the analysis of debris flows for mitigation structures are viscosity and yield strength. The viscosity of flowing debris can be used to calculate velocity and flow depth. Yield strength is used to estimate a critical thickness at which a debris flow will stop moving, which in turn determines deposition and runout. Numerous equations and techniques have been developed to either directly or indirectly measure these properties both in the field and in the laboratory, yet many of these methods are tedious and highly theoretical. Furthermore, debris flows contain significant amounts of coarse-grained materials, which are difficult to sample and test as part of viscosity and yield strength estimation. There is debate as to how much this coarse-grained fraction influences the behavior of a debris flow, especially with respect to critical thickness and runout distances. In order to analyze the effects of gradation on debris behavior, this study compared viscosity and yield strength values obtained in the field, by laboratory measurements, and through analytical derivations. The purpose of the study is to develop a practical and accurate method of determining viscosity and yield strength that can be easily applied to the design of debris flow mitigation structures.