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UBC Theses and Dissertations

A modified hole erosion test (HET-P) to study erosion characteristics of soil Lüthi, Marcel


Today’s increasing demand for energy and natural resources requires safe and reliable infrastructure. This includes hydraulic earth structures like dikes, levees, or dams. Such structures are susceptible to piping, a fundamental type of internal soil erosion. Piping is one of the principal causes of failures and accidents affecting embankment dams. The Hole Erosion Test (HET) is based on soil piping, and is used to determine the erodibility and critical shear stress of a soil. A soil specimen with a preformed axial hole is subjected to a constant-head pressure flow, and the rate of enlargement of the soil pipe is determined indirectly from flow rate and hydraulic gradient. This study presents a Modified Hole Erosion Test (HET-P) that introduces a conventional Pitot-static tube to measure total energy head and flow velocity of the exiting jet, which is correlated to a mean velocity within the axial hole. A series of Modified Hole Erosion Tests (HET-P) was performed on non-erodible PVC specimens with axial holes of constant, but different diameter, followed by HET-P tests on two types of soil, namely glacial till material of a dam core and natural clay deposits from Ontario river banks. Results confirmed that sidewall hydraulic head measurements to determine hydraulic gradients in the standard HET overestimate the resulting axial wall shear stress by as much as an order of magnitude. Furthermore, velocity measurements increase the confidence in test results as they allow for a more direct estimate of the axial hole diameter at any time during a test. A Pitot-static tube used in the HET-P for velocity and pressure measurement can easily be incorporated, and yields more transparent and reliable results by eliminating or amending some of the limiting assumptions of the standard test. It is an easy, fast, and economical approach that can be applied to soils in both constructed earth structures including dams and embankments, and to natural river banks to determine their susceptibility to internal and surface erosion.

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