Rheological Parameters of Norwegian Sensitive Clays, Focusing on the Herschel-Bulkley Model

Abstract

Estimating the run-out distance of a slide is an important part of risk assessment in the planning of infrastruc-ture development in Norway. Numerical models to estimate the run-out distance of sensitive clay slides are currently unavailable. Description of the physics of the slide debris is an important part of a numerical model. Knowledge of the flow behaviour of sensitive clays is at present limited to research on Canadian clays, which have been approximated with the Bingham model.

The flow behaviour of Norwegian quick clay is investigated in this thesis. This is done by conducting visco-metric experiments on clay from Esp and Tiller. The Herschel-Bulkley model is used to find rheological pa-rameters for both Norwegian and Canadian clays.

A total of 19 viscometric tests are performed on Norwegian clays with a coaxial cylinder viscometer. The salinity and liquidity index are changed for different samples to study how these parameters influences the rheological properties.

The Norwegian clays tested show a shear thinning behaviour when subjected to shear. The rheological param-eters show a dependency on liquidity index and salinity. An increase in liquidity index gives decrease in the yield stress and consistency parameter, and an increase in the Herschel-Bulkley exponent. Increase in salinity gives the opposite effect. Relationships between the Herschel-Bulkley parameters and liquidity index are found for Esp clay. These are valid for salinity in the range 1-2 g/L and liquidity index 2.4-4.6.

The set of Herschel-Bulkley parameters found for a flow curve is not unique. If the yield stress is changed, the consistency parameter and Herschel-Bulkley exponent show large change.

Comparing the Herschel-Bulkley parameters for the Canadian and Norwegian clays show that some Canadian clays have similar trend the Norwegian clays. The parameter values are similar at the same liquidity indices, despite of a higher salinity for the Canadian clays. This indicates that yield stress and viscosity also varies with particle size.