DETERMINING RHEOLOGICAL PARAMETERS OF DEBRIS FLOW MATERIAL

A 2.0 m diameter steel 30-degrees inverted cone-and-plate viscometer/rheometer was designed, constructed, and used to test the behaviour of coarse-grained debris flow materials. A 1:5 scale model machine was also constructed and used to test the internal flow dynamics of the viscometer/rheometer and to obtain results for fluids, grain-fluid mixtures, and debris flow fines. For fluids and grain-fluid mixes, our results were similar to those obtained earlier using standard viscometric systems. Derived rheological parameters for debris flow materials and clay slurries agreed well with those determined from calculation, direct measurement, and field observation. Apparent viscosities were shear-rate dependent, extremely sensitive to water content, and as high as 6000 Pa.s. Instantaneous stresses within shearing debris flow material varied over a wide range. Debris flow materials with bimodal grain-size distributions had a dilatant plastic rheology. Those with a low content of coarse material and unimodal grain-size distribution, or exceptionally high fines content, had a plastic or viscoplastic rheology.