Scour and Bridge Hydraulics

Scour in Cohesive Soils

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Abstract

Erosion of clay is in a form of clumps compared to individual particle for sands. The 2012 HEC-18 provides an approach for estimating scour in clays without quantifying the critical shear stress and erosion rate for clays required to perform the design computations. An array of laboratory tests on carefully prepared cohesive soils was conducted to quantify these important parameters. Laboratory erosion tests were conducted in well-controlled flow conditions with carefully prepared artificial Illite clay/sand mixtures. An ex-situ scour testing device (ESTD) provided the needed conditions with 1) directly measured average bed shear stress over 63.5 mm diameter clay samples, 2) consistent boundary roughness throughout the test section, 3) precisely measured flow velocity profiles, 4) automatic soil sample feed maintaining a flush condition between the soil surface and the channel bottom, and 5) clear water conditions around the tested clay for observation. Commercial Illite clay powder, silt powder and non-uniform sands with varied percentages were mixed with water in a vacuum chamber to avoid slaking. Geotechnical properties of clay samples were also measured. An erosion test generally lasted around one hour. During the erosion test, constant bed shear stress controlled the feed rate of the clay samples. Erosion rates for a clay sample at different bed shear stresses and its correlation to corresponding shear stress were obtained through curve fitting. The result was extrapolated to obtain critical shear stress. Relationship of critical shear stress and erosion rate with soil properties were formulated.

How to Cite:

Shan, H. & Kerenyi, K., (2014) “Scour in Cohesive Soils”, National Hydraulic Engineering Conference 2014 1(2014).

Rights: Copyright © 2014, Haoyin Shan and Kornel Kerenyi