Geotechnics, Vol. 6, Pages 48: A Laboratory-Scale Miniature Piezocone Framework for Investigating Rate-Dependent Partial Drainage in Intermediate-Permeability Soils
Geotechnics doi: 10.3390/geotechnics6020048
Authors:
Henrique Milan
André Luis Meier
Gracieli Dienstmann
Helena Paula Nierwinski
Murilo da Silva Espindola
Orlando Martini Oliveira
Rafael Augusto dos Reis Higashi
Penetration rate effects and partial drainage can govern piezocone (CPTu) response in intermediate permeability geomaterials, but field testing at a fixed standard rate limits systematic evaluation. This study presents the development and laboratory validation of a miniature piezocone system and testing framework to investigate rate-dependent penetration response in laboratory-prepared silty sand. Baseline dry and flooded specimens were tested using a triaxial-based configuration at penetration velocities of 9.6, 0.28, 0.10, and 0.03 mm/s, including selected holding periods for dissipation. A dedicated servo-controlled penetration system was then implemented for slurry-prepared specimens, enabling continuous constant-velocity penetration over a wider velocity range (0.004–15 mm/s). Cone resistance was interpreted using normalized net resistance (Q) and normalized velocity (Vh), and pore pressure using normalized excess pore pressure (Δu2/σ′v0). The results show a monotonic rate dependency, with Q increasing as Vh decreases, while Δu2/σ′v0 progressively decreases toward zero at intermediate-to-low Vh; at the lowest rates, pore-pressure readings were affected by instrument signal limitations. A hyperbolic-cosine backbone fitted to the normalized response provided good agreement for resistance (R2 = 0.99, RMSE = 3.41) and more limited agreement for pore pressure (R2 = 0.30, RMSE = 0.23). The drainage transition for the tested material occurs in an interval of approximately Vh ≈ 0.3~30. The study provides a reproducible laboratory approach—combining miniature instrumentation, controlled specimen preparation, and variable-rate penetration—to generate normalized drainage-transition trends for rate-effect investigations in intermediate geomaterials.