Hole Erosion Test: Techniques for Determining the Post-erosion Diameter and Its Uncertainty

To quantify the erosion parameters and thus assess the erodibility of soils, hole erosion tests (HET) are used with methods of interpretation developed recently by researchers. The application of these methods requires some input data, and the most critical one is the final diameter of the eroded hole that is determined after completion of the test. The precision of the hole diameter after erosion leads to a better and more reliable evaluation of the soil’s resistance against erosion, more precisely the soil erodibility characteristics, τ_c (critical shear stress) and k_er (erosion coefficient). In the present study, three methods for determining the final hole diameter are used: M1, direct weighing of the paraffin skeleton of the eroded hole; M2, differential mass of the sample before and after erosion; and M3, 3-D scanning technique of the paraffin skeleton. These methods were applied on five HET tests performed on soil samples containing the same percentage of Armorican kaolinite mixed with Hostun sand. The soil samples are compacted at different densities and to the optimum water content, as determined from a standard Proctor test. The results indicate that method M3 based on a 3-D scanner acquisition and processing of the skeleton volume after erosion compares very well with the more usual ones, M1 and M2, with the obvious advantage of providing the full 3-D reconstruction of the post-erosion hole, allowing further investigations (morphological analyses). Furthermore, an assessment of the uncertainty in predicting erodibility, particularly associated with the post-erosion diameter calculated through the three methods, was conducted and yielded satisfactory outcomes.