Use of fall cones to determine Atterberg limits: A review

Abstract

This paper reviews the percussion-cup liquid limit (LL), thread-rolling plastic limit (PL), and various fall-cone and other approaches employed for consistency limit determinations on fine soil, highlighting their use and misuse for soil classification purposes and in existing correlations. Since the PL does not correspond to a unique value of remoulded undrained strength, there is no scientific reason why plastic limit measurements obtained using the thread-rolling and strength-based fall cone or extrusion methods should coincide. Various correlations are established relating LL values deduced using the percussion-cup and fall-cone approaches. The significance of differences in the strain-rate dependency on the mobilised fall-cone strength is reviewed. The paper concludes with recommendations on the standardisation of international codes and the wider used of the fall-cone approach for soft to medium stiff clays in establishing the strength variability with changing water content and further index parameters.