Volume 35, Issue 4 (July 2012)
A Modified Hole Erosion Test (HET-P) Device
The Hole Erosion Test (HET) is used to determine a critical value of hydraulic shear stress, and hence erodibility, of a compacted soil specimen with a preformed axial hole. A modification to the HET is described, termed the HET-P, in which a Pitot-static tube is introduced at the outlet of the preformed hole. Tests are reported on three specimens of non-erodible PVC with a 6 mm, 12 mm, or 24 mm diameter hole, respectively. Measurements of total energy head and flow velocity of the exiting jet are obtained with the Pitot-static tube, and correlated with mean flow velocity in the hole. HET-P data obtained for non-erodible specimens show the value of hydraulic gradient deduced from measurement of hydraulic head at the sidewall of the standard HET device overestimates, significantly, the hydraulic shear stress on the boundary of the preformed hole. The error varies with size of the hole diameter, and is found to be as much as one order of magnitude.