| dc.description.abstract | The thesis investigates the rheological behaviour of fine-grained slurries in the laboratory using two types of rheometric measuring systems: the vane rheometer and the ball measuring system (BMS). The main purpose is to study how changes in clay/sand ratio, sand grain size, and salinity influence the rheological behaviour of the slurries, and which rheological models best fit the experimental data. There is a discussion of whether the applied rheometric measuring systems can produce reliable rheological data.
The slurries (clay-sand-water mixtures) used in this study have been applied by the researchers at the International Centre for Geohazards (ICG) to investigate the flow dynamics of both subaerial and subaqueous debris flows. Therefore, this study on the rheological properties of the slurries is of significance for their present and future research work.
The investigations reveal that: (1) All the slurries are non-Newtonian yield stress fluids, which exhibit a shear-thinning behaviour at the shear rates less than 10 s-1, but a Newtonian behaviour in the shear-rate range of 10-50 s-1. (2) All the slurries display a rheopectic behaviour at the shear-rate range under consideration. (3) The slurry behaviour is very sensitive to clay/sand ratio, and the yield stress exponentially increases with the increase in clay content. The slurry behaviour is mainly governed by the clay-water matrix, but sand fraction can play a significant role as the clay/sand ratio is very low. The transition from granular to viscoplastic behaviour occurs at a clay content of about 10-15%. (4) The slurry behaviour is also sensitive to sand grain size, and the shear stress level of the flow curve increases with the decrease in sand size. (5) Salinity influences the rheological behaviour of the slurries. There exists a critical low salt concentration that gives a minimum yield stress and apparent viscosity for a slurry. (6) The Herschel-Bulkley model is a good model for fine-grained slurries. (7) Both the vane rheometer and the BMS can produce reliable rheological data for the fine-grained slurries. The BMS may be used at higher shear rates, but it seems to give more reliable results for shear rates lower than 50 s-1.
Some numerical simulations of the downslope slurry movements were also carried out in this study, using the one-dimensional model BING. The simulation results reveal that: (1) The parameters release volume, slope angle, yield stress and viscosity affect the simulation results of the BING code. Runout distance has positive relationship with release volume and slope angle, but negative relationship with yield stress and viscosity. Final deposit thickness has positive relationship with release volume, yield stress and viscosity, but negative relationship with slope angle. (2) The model BING can be used for numerical simulations of muddy debris flows, but the BING code should be modified for the specific cases such as hydroplaning and shear-wetting. Furthermore, the BING code must be modified and extended to model the behaviour of more granular flows.
In further work, the following experiments should be carried out: (1) experiments to determine the pH-values of the slurries and the pHPZC, edge of kaolin mineral in order to better explain the salinity effects and rheopectic behaviour of the slurries; (2) cylinder strength meter tests and inclined plane tests to directly determine the yield stresses of the slurries so that the obtained results from different methods can be compared and evaluated; (3) slurry runout experiments in the laboratory to calibrate the numerical model. In addition, it is of interest to study how the experimental process causes the minimum point in a flow curve in further work. | nor |