Mechanics of the Casagrande liquid limit test

摘要

The liquid limit of soils can be measured using either the cup apparatus developed by Casagrande or by the fallcone method, which is now the standard in much of Europe. This paper will demonstrate, based on a Newmarkian sliding block analysis of the Casagrande percussion test, that these two methods measure different mechanical properties of the soil; the cup test being a measure of specific strength, i.e., strength divided by density, whereas the fall cone is a direct measure of strength. Sources of error in the operation of the percussion test are quantified and a modification to the fall-cone test is proposed to standardize results between the two test methods.