Using Electrical Conductivity to Estimate Properties of Mineral Slurries Used in Drilled Shaft Construction

Abstract An investigation was performed to study the relationships between properties of slurries used in drilled shaft construction. Slurries with different bentonite and attapulgite concentrations, densities, and sand contents were prepared. The Marsh Funnel viscosity, Brookfield viscosity, and electrical conductivity of each prepared sample of slurry were measured. Tests on slurries containing no sand showed that the Marsh Funnel viscosity, the Brookfield viscosity, and the density correlated very well to electrical conductivity because properties of slurries are acquired due to the presence of suspended clay particles, which can be directly correlated to electrical conductivity. The effects of sand content on viscosity and electrical conductivity were investigated. Marsh Funnel viscosity increased slightly with increased sand content. The Brookfield viscosity also showed some variation with sand content. The electrical conductivity increased with increasing clay content. As sand is added to the slurry, the electrical conductivity decreased slowly since the sand particles are inert as compared to the clay particles. The response of electrical conductivity to clay content and sand content was used to develop calibration curves to estimate Marsh Funnel viscosity and sand content as a function of density and electrical conductivity. Few techniques are now available to measure the density of slurry as it varies in the trench. If electrical conductivity is also measured, the viscosity and the sand content at any location of the trench can be estimated. This will improve the QA/QC of slurry construction.