Undrained shear strength degradation and consolidation coefficients evaluation considering a piezoball penetrometer: application on a Brazilian soft soil deposit

This study presents the application of a piezoball penetrometer equipped with pore pressure transducers at the tip, mid-face, and equator positions to characterize the undrained shear strength and consolidation behavior of a soft clay deposit in southern Brazil. Two piezoball tests were performed with cyclic and dissipation measurements, alongside piezocone, field vane, and laboratory tests. Undrained strength estimates based on penetration resistance aligned well with piezocone and vane test results, using an average bearing factor aligned with international practice. Remolded strength revealed sensitivity to the time interval between penetration and extraction readings, with longer delays leading to overestimation. Dissipation tests showed contractive pore pressure behavior, and consolidation coefficients derived from normalized curves at the equator sensor position were closest to piezoconebased values. The study provides practical recommendations for piezoball testing and highlights the importance of time control during cyclic measurements, reinforcing the importance of expanding robust geotechnical databases to support future applications.