A novel approach to estimate soil penetrometer resistance from water content, bulk density, and shear wave velocity: A laboratory study on a loamy sand soil

Continuous estimates of penetrometer resistance (Q) would be useful in root elongation and in soil management studies. However, penetrometers produce estimates of penetration resistance at discrete time points. In this paper, a method with the potential to provide continuous estimates of penetrometer resistance is developed. We use measurements of soil water content, shear wave velocity (Vs) determined from piezo electric devices, and bulk density (ρb) determined with the heat pulse (HP) method, to estimate penetrometer resistance. Soil samples of a loamy sand were packed into cylinders with axial pressures of 50, 100, and 200 kPa, and allowed to equilibrate at matric potentials of −2, −6, −10, −30, −100, −300, and −500 kPa. Thermal conductivity (λ), Vs and Q were measured after equilibration. A λ-based approach was applied to estimate ρb, and small strain shear modulus (G) was calculated from ρb and Vs. Our results confirmed a linear relationship between Q and G (where G = Vs2ρb), which provides a basis to estimate penetrometer data in the field using buried sensors and a physically based model.