Direct determination of rheological characteristics of debris flow

TO predict debris flow characteristics it is necessary to determine the rheological properties of these mixtures. It is suggested that such a mixture can be obtained by adding successively to clear water, coarser particles derived from a sample of the debris flow material. At each addition different suspensions are obtained that can be considered as progressively coarser interstitial fluids of the complete mixture. These suspensions are easier to test and their rheological properties can thus be determined. The behavior of the complete material can then be inferred from these results. This procedure has been adopted for a debris flow which occurred on Moscardo Torrent (Friuli Region, Northeastern Italy) in 1995. A wide range of rheometrical techniques have been used to determine the rheological characteristics, such as laboratory rheometer, inclined plane test, large-scale rheometer, and field tests. The rheological parameters and behavior type of the complete material have been inferred from the yield stress-solid fraction curve and from the flow curve evolution. The behavior has been found to be mainly viscoplastic and representable by a Herschel-Bulkley model.