Scour and Bridge Hydraulics

Scour in Cohesive Soils

  • Haoyin Shan (TFHRC)
  • Kornel Kerenyi


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

Publisher Notes

  • Panel moderated by Dave Claman, IOWADOT.
  • About the Presenters: Dr. Haoyin Shan is a Hydraulic Research Engineer at Genex Systems. He holds a M.S. degree in Environmental Hydraulics from Sichuan University in China in 2006. He received his Ph.D. degree in Civil Engineering from The University of Nebraska-Lincoln in 2010. He has been active in areas of open channel flows, bridge hydraulics and sediment transport. His current research involves study of scour in cohesive soils using an Ex Situ Scour Testing Device, and development of In Situ Scour Testing Device.

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Published on
21 Aug 2014
Peer Reviewed