Measurement uncertainty of the fall cone (FC) test

Abstract

The most common method to determine liquid limit, sensitivity and undrained shear strength of clay in Nordic countries is to use fall cone test (FC). However, all these properties include some uncertainty arising from different sources e.g. the geological conditions, test procedure and sample disturbance. In this study, the measurement uncertainty of the fall cone test was analysed. The parameters of interest were the penetration depth of the cone and the interpreted intact undrained shear strength. The test set consisted of high-quality block samples (d=132mm) collected from six different depths at soft clay site in Finland. The diameter of the samples made it possible to perform four parallel fall cone tests per depth, so total of 24 fall cone tests were done. The calculated COV-values for each parameter at each depth were between 0.02 and 0.08, thus indicating very low measurement uncertainty. These values also included the inherent variability of the soil. Overall, the results showed that the fall cone test is reliable method for determining the intact undrained shear strength, if the test is done with care.