Revised plastic soil classification system with soil behaviour type index based on CPTu

The properties of soils are highly complex, and therefore, the classification system should be based on multiple perspectives of soil properties to ensure effective classification in geotechnical engineering. The current study of research demonstrates a lack of correlation between classification systems based on soil plasticity and those based on in-situ mechanical properties of soils. A CPTu-based plasticity classification system is proposed using the soil behaviour type index (I_c), with its reliability and limitations discussed. The results indicate that (1) I_c has the capacity to predict the stratigraphic distribution from the in-situ mechanical properties of soils. It showed a significant linear correlation with w_L, which soil classification zone was similar to that of clay factor (C_F); (2) A CPTu-plasticity classification system is proposed to characterize both plasticity and in-situ mechanical properties of soils. This system allows for the initial classification of soils solely based on CPTu data. Furthermore, it has been established that I_c = 2.95 can delineate the boundary between high- and low-compressibility soils. (3) The error is only 25.2% relative to the Moreno-Maroto classification chart, and the system tends to classify soils of intermediate nature as clay or silt. The distance between the data points and both the C-line and the new C-line (ΔI_p, ΔI_pIc) showed a significant positive correlation. Only one data point was misclassified, considering human error in measuring I_p. (4) The new classification chart has been found to be more applicable to offshore and marine soils.