Influence of penetration rate on CPTU measurements in saturated silty soils

Drainage behaviour of intermediate soils (e.g. silts, sandy silts, clayey silts) during standard cone penetration rate (20 mm/s) typically falls between that of sand and clay, for which fully drained and fully undrained conditions are expected to apply, respectively. Partial drainage phenomena may be evaluated by varying the penetration rate within a range which depends on the consolidation characteristics of the soil to be tested. This paper presents the results of a variable rate piezocone test (CPTU) campaign carried out in a clayey silt deposit of the southern margin of the Po river valley (Forlì, Italy). In order to assess the in situ drainage conditions, normalized piezocone measurements have been interpreted in terms of a non-dimensional penetration rate. In this way, it is potentially possible to detect the transition point from undrained to partially drained and drained responses. Results have been compared to previously reported data on both natural deposits and laboratory reconstituted soils.