Estimation of Effective Internal Friction Angle by Ball Penetration Test: Large-Deformation Analyses

The ball penetrometer is a full-flow penetrometer used as an alternative to the traditional cone penetrometer for characterizing the strength of soft sediments, particularly for offshore engineering, due to its large projection area. However, if the ball is penetrated under partially drained conditions, the resistance of the ball changes with the penetration velocity. The performance of ball penetration is examined employing a coupled large-deformation finite-element method. The reliability of numerical simulations under undrained and partially drained penetrations is verified by comparing with previous tests in the chamber and centrifuge. The backbone curve determining the penetration resistance on the spherical probe is proposed to quantify the influence of partially drained conditions, which captures the effect of the ratio of the diameters of the shaft and ball. Base on the backbone curve derived, an interpretation approach is proposed to predict the effective internal friction angle using the net resistance measured in the ball penetration tests with different penetration velocities.