Assessment of Equilibrium Scour by a Submerged Circular Turbulent Impinging Jet in Cohesive Soils

Abstract

In this paper, results from a study where detailed measurements of the time development of the scour holes produced by a submerged circular vertical impinging jet in cohesive soils from long-term scour tests are presented. This is the type of jet used in the ASTM standard Jet Erodiblity Test, which relies on measurements of the time development of scour for prediction of soil erodibility parameters. In the experiments, measurements of the entire scour hole were taken after scouring times of 5 min, 10 min, 15 min, 20 min, 30 min, 40 min, 50 min, 1 h, 1.5 h, 2 h, 4 h, 8 h, 16 h, 24 h, and then at an interval of 24 h thereafter until the scour hole was considered to have reached equilibrium. The measurements were taken on a 2 mm grid using a computer-controlled laser displacement meter. For the tests, two types of manufactured pottery clays were used. The growth of the maximum depth of scour, average scour hole radii, centerline depth of scour, and scour hole volume were evaluated. It was seen that the characteristic dimensions of the scour hole that have been typically been used to assess equilibrium state, namely, the maximum and centerline scour holes, come to equilibrium more quickly than other locations in the scour hole. Results also showed the Sumer et al. (1993) model for predicting the time development of scour worked well for the present tests.