Impact of Using Measured v. Corrected Tip Resistance Values in PCPT-Based Soil Characterization and Modeling

Cone Penetration Test (CPT) and Piezocone Penetration Test (PCPT or CPTu) based analysis and modeling are acknowledged as accepted tools for in-situ subsurface investigations and soil characterization. The CPT/PCPT provides continuous sounding of subsurface sediments and, in simple terms, conducted by advancing a cylindrical rod with a cone tip down into the soil. During penetration, the cone penetrometer simultaneously measures the cone tip resistance and sleeve friction. When PCPT is used, the pore pressures generated during penetration can also be measured. Due to the geometric design of the piezocone, pore water pressures generated behind the cone base can influence the total stress measured by the cone tip. Therefore, the measured cone tip resistance may have to be corrected for certain cone configurations to account for the effect of this pore water pressure developing behind the cone tip. Theoretically, the corrected cone tip resistance is calculated by adjusting the measure value using an effective area ratio. This paper presents a comparison of using measured and corrected tip resistance values for soil characterization purposes using two of the commonly accepted classification models; Zhang/Tumay Probabilistic (1999) and Robertson et al. (1986) methods. Analysis of two sites are included to illustrate the differences.