Reliability of CPT Ic as an index for mechanical behaviour classification of soils

Abstract

This paper presents results of an analysis of a set of high-quality, side-by-side piezocone penetration test (CPTu) and standard penetration test (SPT) data for examining mechanical behaviour-based classification of soils. The results show that the soil behaviour type index (Ic), either defined by Jefferies and Been (denoted herein as Ic,BJ) or by Robertson and Wride (denoted herein as Ic,RW), is an effective parameter for mechanical behaviour classification. Additionally, an effort is made to find the most suitable Ic cut-off (or boundary) value that can delineate cohesionless (sand-like) soils from cohesive (clay-like) soils. The Robertson and Wride's formulation, Ic,RW = 2·67 is found capable of delineating these two classes of soils. Similarly for the Been and Jefferies' formulation, Ic,BJ = 2·58 is found to be the most suitable Ic cut-off value for such classification purpose. These cut-off Ic values for distinguishing sand-like soils from clay-like soils are found to be reliable in a case study of liquefaction susceptibility.