A novel vibro-penetration test (VPT) for the investigation of cohesionless soils in the field

A novel dynamic penetration testing method for the investigation of cohesionless soils based on the principles of vibratory driving has been developed. During the so-called vibro-penetration test (VPT), a vertical harmonic excitation force drives a rod with a conical tip into the ground. The penetration resistance is defined as the number of excitation cycles N_z10 required for 0.10 m penetration with a reference driving energy. In order to evaluate N_z10, the tip and shaft resistance, the tip acceleration and the depth of the penetrometer tip are recorded during driving and the data are evaluated according to a proposed vibro-penetration model. Experimental and numerical investigations are carried out to investigate the soil response, validate the mechanical model and evaluate the influence of the density, the effective stresses and the machine parameters on the vibro-penetration resistance. The results show that the N_z10 – values are reproducible, correlate unambiguously with the state variables but depend on the machine parameters to some extent. In comparison with the CPT, the VPT shows similar sounding records. However, the required equipment is much lighter, the execution faster and in-situ investigations of medium dense to dense cohesionless soils at large depths are feasible.