American Society of Civil Engineers


Scour at Vertical Piles in Sand-Clay Mixtures under Waves


by Subhasish Dey, (corresponding author), (Professor and Brahmaptura Chair, Dept. of Civil Engineering, Indian Institute of Technology, Kharagpur 721302, West Bengal, India. E-mail: sdey@iitkgp.ac.in), Anders Helkjær, (Civil Engineer, Grontmij-Carl Bro A/S, Port and Marine Engineering, Granskoven 8, DK-2600 Glostrup, Denmark. E-mail: anders.helkjaer@grontmij-carlbro.dk), B. Mutlu Sumer, (Professor, Section of Coastal, Maritime and Structural Engineering, Dept. of Mechanical Engineering (MEK), Technical Univ. of Denmark, DTU Building 403, DK-2800 Kgs Lyngby, Denmark. E-mail: bms@mek.dtu.dk), and Jorgen Fredsoe, (Professor, Section of Coastal, Maritime and Structural Engineering, Dept. of Mechanical Engineering (MEK), Technical Univ. of Denmark, DTU Building 403, DK-2800 Kgs Lyngby, Denmark. E-mail: jf@mek.dtu.dk)

Journal of Waterway, Port, Coastal and Ocean Engineering, Vol. 137, No. 6, November/December 2011, pp. 324-331, (doi:  http://dx.doi.org/10.1061/(ASCE)WW.1943-5460.0000095)

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Document type: Journal Paper
Abstract: Marine sediments often contain sand-clay mixtures in widely varying proportions. This study presents the results of equilibrium scour and time variation of scour depths at circular piles embedded vertically in clay alone and sand-clay mixed beds under waves. Experiments were conducted in a wave flume with different proportions of sand-clay mixtures as bed sediments. Test results for the cases of steady current and sand alone under waves are used as references. The equilibrium scour depth reduces with an increase in clay proportion n (by weight) in a sand-clay mixture. Interestingly, the scour depth reductions for n=0.3 and 1 are almost equal, suggesting that when the clay proportion in a sand-clay mixture becomes 0.3, the sand-clay mixture behaves as if it were a clay-alone mixture, in relation to scour depths. The dependency of equilibrium scour depth on the Keulegan-Carpenter number for different n-values can be expressed by an exponential law, using different coefficients and exponents. For time variation of scour, the nondimensional timescale increases with an increase in Keulegan-Carpenter number and clay proportion. However, unlike the near-equal scour depths, timescales are quite different for n=0.3 and 1.


ASCE Subject Headings:
Erosion
Hydraulics
Scour
Piles
Water waves
Clays
Wave velocity

Author Keywords:
Erosion
Hydraulics
Scour
Piles
Water wave
Wave velocity