EXPERIMENTAL STUDY OF DEBRIS FLOWS

摘要

The authors provide an interesting series of systematic velocity and concentration distribution measurements for grain-water mixture flows on a steep slope. However, concerning the content of the paper, the writers find it useful to raise the following issues related to current views in the field of debris flows and rheology. The paper's title contains the expression "debris flows," and the introduction and list of references clearly show that this paper is devoted to what are usually called debris flows. However, the authors present experiments on grain-water mixture flows at concentrations ranging from 2.5 to 43.5% in volume. Within such a concentration range, except for extremely rapid flows, sand-water mixtures are heterogeneous and must be regarded as two-phase flows (as proved by the authors' results). Unlike the authors' apparent view, when considering either the usual concepts of debris flows or definitions proposed in literature (Davies 1986; Pierson and Costa 1987) or field observations (Pierson 1986; Takahashi 1981), the expression "debris flows" refers to "one-phase" flows or "pseudo-one-phase flows." This means that the relative velocity between the different components, that is, water, silt, sand, pebbles, and boulders, is generally very small and the main part of the mixture (body + front) can be globally considered as a homogeneous fluid (even if there are lateral deposits and a more or less large longitudinal concentration gradient). The experimental study presented must be essentially related to intense solid transport of fine material only. Unlike debris flows, for these phenomena, the flowing mixtures cannot be considered homogeneous (Pierson and Costa 1987; Meunier 1991).