3D finite element simulation of a single-tip horizontal penetrometer-soil interaction. Part II: Soil bin verification of the model in a clay-loam soil

Horizontal penetrometers have been recently examined as instruments for on-the-go mapping of soil strength/compaction. Since the horizontal penetrometer resistance (PR) provides a composite soil strength parameter, it needs to be characterized with respect to variations in soil physical properties as well as standardized with respect to the operational parameters of the device. In a recent study, a 3D finite element (FE) model was developed for a single-tip horizontal penetrometer-soil interaction (cf. Part I of this study; Naderi-Boldaji et al., 2013b) and the effect of some soil/operational parameters (mechanical properties of soil, model boundary effects, penetrometer tip extension, working depth and soil failure mode ahead of the tine) on PR was investigated. In the second part of this study, two soil bin tests were conducted to evaluate the PR predictability of the FE model. This is a crucial step for finite element modelling of soil compaction reflected by PR as affected by soil water content, bulk density and texture. The soil bin tests were carried out in a clay loam soil at two different water contents of 0.171 and 0.183 g g(-1) and dry bulk densities of 1.64 and 1.59 Mg m(-3), respectively, to evaluate the model at two different levels of PR. The soil elastic parameters (i.e. Young's modulus of elasticity and Poisson's ratio) were estimated from oedometer (uniaxial compression) tests on confined and unconfined undisturbed samples taken within the working depth of the penetrometer whilst the plastic parameters (the parameters of the Drucker-Prager constitutive model) were determined by triaxial tests at three levels of confining stress. The results indicated the practical and efficient use of oedometer tests for estimating soil elastic parameters for numerical simulations. The FE model predicted the measured PR with a small error (<12%) when modelling the soil as elastic-perfectly plastic material, whilst the prediction error was found to be significantly higher when soil hardening was included. This may suggest that the confinement of soil around the moving cone is different than in a confined compression test. It is concluded that the FE model presented here and the procedures used for estimation of the model input parameters reflected well the change in soil physical conditions of the two tests. Further evaluations are needed to generalize the model predictions across soil types and characterize PR with respect to soil physical properties. (C) 2014 Elsevier B.V. All rights reserved.