Abstract: Ball penetrometers are particularly advantageous for predicting the undrained shear strength of clays in marine geotechnical investigations, due to their larger projection area compared to traditional cone penetrometers. However, if the ball penetrates silty clay or clayey silt, the surrounding soil may experience partially drained conditions, which can affect penetration resistance. Previous studies have focused on normally consolidated soils and have not been able to consider the coupling of partial drainage conditions with the overconsolidation ratio. A large deformation finite element method utilizing effective stress is utilized to model the deep penetration of the ball into overconsolidated soils. The reliability of the large deformation simulation was validated by comparing it with centrifuge tests and field measurements. A backbone curve of penetration resistance at the spherical probe is developed, establishing a relationship between penetration resistance and partial drainage conditions in overconsolidated soils. Based on extensive parametric analyses, a novel approach is proposed to predict the effective internal friction angle of overconsolidated soils using penetration resistance data from ball penetration tests. The normalized penetration rate can quantify the degree of partial drainage, eliminating the need to measure pore pressure during penetration.

Key words: ball penetrometer, silty clay, overconsolidation, effective internal friction angle, large deformation finite element