Effect of Critical State Line curvature on Cone Penetration Test-based state inference in sand

The in-situ state of granular materials is usually inferred from the results of cone penetration test measurements. That inference is frequently based on critical state soil mechanics concepts such as the existence of a critical state line (CSL) for the material. Most often the CSL assumed for CPT interpretation is log-linear in the compression plane. However, it is known that particle crushing induces curvature on CSLs at stress levels similar to those measured by a CPT. It is still unclear to what extent CSL curvature affects state inference from CPT and what risks are introduced when it is ignored in practical applications. To answer those questions, we carry out full geometry simulations of the cone penetration test (CPT) in sand using the Particle Finite Element method. Different material models are employed for Ticino Sand. One employs a curved CSL that matches closely the experimental result across all the stress range. Others use approximations to that curve that are only valid in a specific stress range. Simulations are carried out with all models and then compared with the results of the laboratory calibration chamber database. The simulation results show that including CSL curvature significantly improves model performance and that state inference based on a log-linear CSL fitted at a low stress range may be dangerously misleading.