The influence of pore pressure gradients in soil classification during piezocone penetration test

The standard cone penetration test (CPT) measures the resistance at the tip (qc) during constant rate of penetration as well as the friction/adhesion along the sleeve (fs). The excess porewater pressures generated as a result of the penetration can also be measured by a piezometer/transducer (u2) located immediately behind the cone (CPTU). The collected data help to identify several physical, hydraulic and mechanical properties of the soil layers. However, the main function of the test is soil classification. Classification has been done by using the qc and fs values at the early stages to be followed by incorporating the concept of soil behaviour type index Ic. Soil behaviour type (SBT) index calculates Ic and is generally calculated by normalised values of tip resistance and sleeve friction: Q and F, respectively. The porewater pressure component in the relationship is accounted for by the coefficient Bq. A clear distinction between the soil classes cannot be made due to limited coverage of the parameters employed. A new parameter “i” which contributes significantly to the classification process by the use of varying porewater pressure values Δuw by depth is introduced in this paper to improve the value of Ic in the classification procedure.

► A new parameter “i” proposed to classify soils with cone penetration test data.
► A new soil type behavior index “Ic” proposed.
► A new soil classification chart with seven zones has been developed.