Comparison of rheometric devices for measuring the rheological parameters of debris flow slurry

Soil samples with clay content ranging from 15% to 31%, were taken from three debris flow gullies in Southwest China. Three debris flow slurry samples were prepared and tested with four measuring systems of an Anton Paar Physica MCR301 rheometer, including the concentric cylinder system, the parallel-plate system, the vane geometry, and the ball measuring system. All systems were smoothwalled. Flow curves were plotted and yield stress was determined using the Herschel-Bulkley model, showing differences among the different systems. Flow curves from the concentric cylinder and parallelplate systems involved two distinct regions, the low shear and the high shear regions. Yield stresses determined by data fitting in the low shear region were significantly lower than the values from the inclined channel test which is a practical method for determining yield stress. Flow curves in the high shear region are close to those from the vane geometry and the ball measuring system. The fitted values of yield stress are comparable to the values from the inclined channel test. The differences are caused by wall-slip effects in the low shear region. Vane geometry can capture the stress overshoot phenomenon caused by the destruction of slurry structure, whereas end effects should be considered in the determination of yield stress. The ball measuring system can give reasonable results, and it is applicable for rheological testing of debris flow slurries.