Investigation into the effect of uncertainty of CPT-based soil type estimation on the accuracy of CPT-based pile bearing capacity analysis

Cone Penetration Test (CPT or CPTu) is commonly used for estimating soil types and also for the geotechnical design of pile foundation. However, the level of agreement between the CPT-based soil types and the traditional identification of soil types based on samples may vary significantly; and it is not clearly understood if this variation has any sort of relationship with the CPT-based pile design. To investigate into this area, a ground investigation trial was carried out at six different locations as part of a highway scheme in East of England. At each location the trial comprised one CPTu adjacent to one borehole (BH) with conventional sampling and laboratory testing. The soil types were estimated from the CPTs and compared with the boreholes findings, and the levels of correlation between them were established. Similarly, the ultimate bearing capacity of a typical bored pile based on the CPTs and on the BHs were calculated and compared. Despite the variable level of disagreement of the CPT-based soil type estimation with the BHs findings, the pile capacity based on CPT data was found to be generally consistent with the values obtained from the traditional BHs-based pile design.