A new approach to the correlation of SPT-CPT depending on the soil behavior type index

Abstract

In this study, a model based on soil behavior type index (Ic) has been proposed for the conversion of field cone penetration test (CPT) data to the standard penetration test (SPT) blow counts (N). The field data used in the study were obtained from the fluvial soils formed by the Sakarya river in Adapazarı (Turkey). According to the proposed model, it is understood that there are exponential relationships between SPT-N and CPT data with varying coefficients (constant multipliers and exponents) for different Ic intervals. While the coefficients of the equations were kept constant in the previous formulations developed based on Ic, the current study revealed that the mentioned coefficients should be changed for different Ic intervals. The normalized cone resistance (qt/ Pa) or corrected SPT-N values (N60), found with the model created with the final coefficients, were evaluated. The results obtained by using the new model proposed in this paper were compared with other models generally accepted in the literature. It has been revealed that the results achieved by this new model are the closest ones to the measured values compared to the other methods. To verify the proposed model, CPT-SPT data pairs that were not used in the model generation were analyzed. Verification analyses confirmed that the developed method has given more realistic results than the other methods suggested in the literature. It was understood that the error rate in the model, in which conversion between CPT and SPT data can be made by considering the variability in the soil behavior type index, is lower than the others. As a result, the paper gives a new perspective by introducing a simple and newly updated form of estimating N60 values.