Application of micro-computed X-ray tomography for improving the hole erosion test analysis on high plastic clay

The hole erosion test (HET) was developed to simulate piping erosion and to study the erosion parameters of cohesive soils. The erosion rate in the HET is evaluated by the enlargement of a pre-performed hole in the axis of the specimen with time. The hole diameter during the test is estimated using the pipe flow theory with an assumption that the friction factor varies linearly with time. To investigate this assumption, measurements of the hole diameter during the test are needed. So far, there have been no measurements of the hole diameter during the HET and the hole diameter is measured only at the end of the test after cutting the specimen. In this study, a novel approach to measure the hole diameter at different time steps during the HET using micro-computed X-ray tomography (µCT) is presented. Combining the HET and µCT data, the assumption regarding the friction factor was investigated. Moreover, a linear relation between the flow rate and the hole diameter was found in the range of the tested diameters. This relation was confirmed with HETs using non-erodible PVC specimens with different hole diameters. Accordingly, a new method to interpret the HET for high plastic clay was proposed, in which the hole diameter is calculated based on the flow rate, given that the initial and the final hole diameters are known. A comparison between the analysis of the HET using the proposed and the previous analysis methods is presented.