Effects of fall-cone test on classification of soils: some considerations from study of two engineering earthworks in Central Italy

Abstract

This work, based on the data of two earthworks recently completed on two sites near Lake Trasimeno (Central Italy), examines the consequences of the enforcement in Europe of the fall-cone test for the Liquid Limit (LLcone) instead of the Casagrande cup (LLcup). This new standard has been incorporated in the latest Italian soil classification (UNI 11531-1:2014), substituting the previous one (UNI 10006:2002). A set of 28 soil samples was analysed: the research shows that LLcone is always greater than LLcup. According to the old standard, all samples were suitable for the works planned but, according to the new one, 18 % of samples became unsuitable. This is in spite of the fact that there is nothing to show that the old classification was “unsafe.” The new standard (based on LLcone) restricts the choice of materials, so that not only will costs for earthworks increase in the future but, paradoxically, because of the new standard, thousands of kilometers of properly working old levees became suddenly “unsafe.” The results suggest that soil classification criteria for earthworks should be reconsidered in order to transform the conventional “index properties” to sound physical characteristics.