Correlation between cone resistance with standard penetration value for predicting consistency of cohesive soil in Eastern India

In the geotechnical engineering field, the rapid speed of urbanization triggers the need for direct measurements of sub-soil parameters through in situ testing, accompanied by instant results. At this juncture, the cone penetration test (CPT) is selected for this study. Here, an attempt is made to develop a correlation between cone penetration resistance (q_c) and standard penetration blow count (SPT N) in order to predict a reference range of q_c for cohesive (silty clay/clayey silt) sub-soil of different SPT-based consistencies. In this context, 25 CPT were conducted adjacent to conventional boreholes accompanied by SPT tests at eight important locations in West Bengal (WB) and Odisha (OR), India, focusing on infrastructure development. Primarily, sub-soil is characterized by bulk unit weight (γ) along with soil behavior type index (I_C) estimated from the CPT and compared with the sub-soil profile identified from conventional boreholes. Further, a comparison of q_c with SPT N is made to establish a correlation. Also, an attempt is made to tally the established correlation with the earlier correlations established for different regions. This study quantitatively establishes a quadratic correlation (R² = 0.84) between q_c and SPT N, which is found to be in good agreement with the previous correlations. Overall, the key findings of this study, i.e., the predicted range of q_c, reveal a reliable method for assessing the consistency of cohesive sub-soil by virtue of the q_c. However, this correlation is limited to soft to very stiff silty clay/clayey silt sub-soil formation.