CPTu-Based Soil Behaviour Type Indexes that are Independent of Sleeve Friction Readings: An Application in Tailings

The piezocone penetration test (CPTu) is widely used for in situ geotechnical characterisation. One of the most common uses of the CPTu is the characterisation of the soil stratigraphy. Assessment of the stratigraphy is often aided by two-dimensional charts that are divided into regions that correspond to different soil behaviour types. The implementation of these charts can be facilitated by soil behaviour type (SBT) indexes which are functions of the parameters that plot along the two axes of the SBT charts. These functions are defined in such a way that contours of the function coincide, at least approximately, with the internal boundaries of the SBT charts. It appears that the two best known SBT indexes are a function of the sleeve friction reading of the CPTu. Herein we raise awareness around two additional SBT indexes that are independent of sleeve friction. These additional SBT indexes may be useful supplements to the better-known indexes that depend on sleeve friction measurements. The implementation of the indexes is illustrated using CPTu data from iron ore tailings although the concepts discussed herein are applicable to any type of soil.