Abstract: The piezocone penetration test (CPTU) is widely applied in soil layer division and soil classification. However, its various soil classification methods have certain applicability and limitations. Five common classification charts are analyzed based on two groups of practical engineering cases. The results show that the existing classification chart can well distinguish cohesive soil and non-cohesive soil, but there are certain errors in the discrimination between silty clay, silty and silty sand. Besides, most classification charts adopt the transitional zone method, which will underestimate the classification accuracy. In this study, according to the actual test data classification results, the soil behavior type index Ic is modified through the soil behavior type index classification chart by Robertson. As a result, a new method of CPTU based modified soil behavior type index is proposed by modifying the concentric circle model to a parallel line model. The application results show that the proposed classification method can well satisfy the classification of practical engineering soil and the discrimination between silty clay, silty soil and silty sand, respectively.

Key words: piezocone penetration test (CPTU), soil classification, modified soil behavior type index, soil behavior type index classification chart