Determination of liquidity index of glacial tills based on the fall cone single point methods

Liquidity index (IL) is one of the basic geotechnical parameters of cohesive soils. It defines the consistency and physical state of soil. Since the state of the cohesive soil determines the bearing capacity of the subsoil, the value of IL is often used for various correlations used in the design of foundations. The cone penetrometer is a device used to determine the liquid limit (wL) based on which the value of the liquidity index is calculated according to both Polish (PN-88/B-04481) and European (PKN-CEN ISO/TS 17892-12) standards. In this method the liquid limit is read out from the relationship between the moisture content of soil paste and the depth of cone penetration. This relationship must be determined by interpolation between at least four test points. However, several, so-called single point methods, can be found in the literature. They are to be used for a quick and efficient measurement of the liquid limit using existing empirical correlations. This article discusses the possibility of applying some of those methods to calculate the value of the liquidity index for selected cohesive soils. The analysis was carried out on ablation and subglacial tills which occur in northern and north-western Poland. Based on the test results it is concluded that the empirical formulae used in the single point methods have a limited application and should be used with caution taking into account the type, genesis and mineral composition of examined deposit.