Normalisation of Rate Effects during Piezocone Penetration Testing: A Numerical Study

  • Hauser, Laurin (UPC)
  • Monforte, Lluís (CIMNE)
  • Arroyo, Marcos (UPC)
  • Schweiger, Helmut (TU Graz)

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Intermediate soils are well known to behave in a partially drained manner during in-situ testing, such as piezocone penetration testing (CPTu). This may lead to unrealistic soil parameters when standard interpretation methods, which typically assume either fully drained or undrained behaviour, are adopted. Different approaches to normalise the rate effect during penetration have been developed considering, e.g., the permeability and compressibility of the soil, as well as the penetration velocity and the cone diameter. The present work aims to investigate a simplified normalisation approach adopting the velocity factor Vh according to Schnaid et al. [1] based on numerical simulations of CPTu using the application G-PFEM, an implementation of the Particle Finite Element Method (PFEM) for geomechanical problems [2]. The analyses consider different stiffnesses, stress levels, and strength properties of normally consolidated soils, while partially drained conditions are obtained by varying the ratio between penetration velocity and soil permeability. The results underline that the velocity factor Vh, depending on the penetration velocity, the cone diameter, the soil rigidity index Ir, and the pore pressure dissipation time t50, is a suitable measure for describing the evolution of normalised tip resistance Qt and pore pressure U2 over the drainage spectrum. However, a modified range for partial drainage is found, resulting in larger Vh values for both the lower drained and upper undrained boundaries, which agrees with field observations reported in the literature. Furthermore, the study shows that the numerical simulation of CPTu can contribute to an improved interpretation of the in-situ test by providing additional data, such as the corresponding drained or undrained limiting cases. [1] F. Schnaid, G. Dienstmann, E. Odebrecht, and S. Maghous, “A simplified approach to normalisation of piezocone penetration rate effects”, Géotechnique, Vol. 70, No. 7, pp. 630–635 (2020). [2] J.M. Carbonell, L. Monforte, M. Ciantia, M. Arroyo, and A. Gens “Geotechnical particle finite element method for modeling of soil-structure interaction under large deformation conditions”, Journal of Rock Mechanics and Geotechnical Engineering, Vol. 14, No. 3, pp. 967-983 (2022).