Cone penetration at variable rates in kaolin–sand mixtures

The degree of drainage that occurs during cone penetration is a crucial factor in the derivation of soil properties from cone penetration tests (CPTs). Fines content, especially clay fraction, has a significant effect on the soil's drainage characteristics as well as on its compressibility and strength. This paper presents the CPT results performed at variable penetration rates in a drum centrifuge and in a pressure chamber. The soils that are investigated are normally consolidated and comprise fine sand with varying proportions of kaolin clay (5, 10 and 25% by dry weight) as well as pure kaolin clay. A significant influence of kaolin content on CPT rate dependency is observed and this dependency is seen to be similar in both the centrifuge and pressure chamber experiments. A series of supplementary soil element tests using the Rowe cell and simple shear test apparatus is used to improve interpretation of the experimental results and investigate the suitability of a normalised velocity term to define the drainage conditions around penetrometers.