Effects of Bed Compaction on Scour at Piers in Sand-Clay Mixtures
Publication: Journal of Hydraulic Engineering
Volume 139, Issue 9
Abstract
Scour at piers embedded in a bed of cohesive sediment mixture is investigated to quantify the effects of bed compaction. Experiments were conducted in a large rectangular laboratory flume with natural clay sediment collected from a stream located at the Chilean coastal range. Nonintrusive and high-resolution topographic measurements of scoured bed in the vicinity of piers were performed during the experimental runs with an installation of a laser distance sensor (LDS) that was traversed by the precision step motors. Measurements were taken by the LDS in different azimuthal half-planes to study the spatiotemporal variation of the topography of evolving scour holes. Experiments were conducted over 40 h, until an advanced stage of scour was reached, with the approaching flow having a bed shear stress equaling 95% of the Shields critical condition for the initiation of motion of sand in a sand-clay mixture. Results show that the bed is successively scoured in three different forms, chunks of aggregates, aggregate by aggregate, and particle by particle, when increasing the ratio of actual to Proctor’s optimum molding water content, . Maximum scour depth was mainly observed at the wake region (downstream of the pier) and ranged from 10 to 58% of that in the sand alone case for mixtures with the same size of the sand fraction. For a given compaction energy, scour depths first decrease with , up to a value of , as fine clay particles are flocculated and increasingly dispersed with water content. For values of , the sediment matrix behaves as a fluid mud. In the latter case, scour depths increase with water content as the sediment bed becomes increasingly liquid.
Get full access to this article
View all available purchase options and get full access to this article.
Acknowledgments
This study is the part of the research project Fondecyt 11080126 funded by the Chilean Research Council, Conicyt. The authors thank C. Meier for his suggestions to improve the content of the paper.
References
Ansari, S., Kothyari, U., and Ranga Raju, K. (2002). “Influence of cohesion on scour around bridge piers.” J. Hydraul. Res., 40(6), 719–729.
Berlamont, J., Ockenden, M., Toorman, E., and Winterwerp, J. (1993). “The characterisation of cohesive sediment properties.” Coastal Eng., 21(1–3), 105–128.
Briaud, J.-L., Ting, F., Chen, H., Cao, Y., Han, S., and Kwak, K. (2001). “Erosion function apparatus for scour rate predictions.” J. Geotech. Geoenviron. Eng., 127(2), 105–113.
Cornell University. (1951) “Final report on soil solidification research,” Ithaca, New York.
Debnath, K., and Chaudhuri, S. (2010). “Bridge pier scour in clay-sand mixed sediments at near-threshold velocity for sand.” J. Hydraul. Eng., 136(9), 597–609.
Dey, S., Helkjær, A., Sumer, B. M., and Fredsoe, J. (2011). “Scour at vertical circular piles in sand-clay mixtures under waves.” J. Waterw., Port Coastal Ocean Eng., 137(6), 324–331.
Diab, R., Link, O., and Zanke, U. (2010). “Geometry of developing and equilibrium scour holes at bridge piers in gravel.” Can. J. Civ. Eng., 37(4), 544–552.
Lambe, T., and Whitman, R. (1951) “Soil mechanics,” John Wiley, New York, 553.
Link, O., Pfleger, F., and Zanke, U. (2008). “Characteristics of developing scour-holes at a sand-embedded cylinder.” Int. J. Sediment Res., 23(3), 268–276.
Mehta, A., and McAnally, W. (2008). “Fine-grained sediment transport.” Sedimentation engineering: Processes, measurements, modeling, and practice, ASCE Press, Reston, VA.
Molinas, A., Jones, S., and Hosny, M. (1999). “Effects of cohesive material properties on local scour around piers.” Transportation Research Record 1690, Transportation Research Board, Washington, DC.
Partheniades, E. (2009). Cohesive sediments in open channels: Properties, transport, and applications, Butterworth-Heinemann, Burlington, VT.
Richardson, E., and Davis, S. (2001). “Evaluating scour at bridges.”, 4th Ed., U.S. Dept. of Transportation, Washington, DC.
Ting, F., Briaud, J., Chen, H., Gudavalli, R., Perugu, S., and Wei, G. (2001). “Flume tests for scour in clay at circular piers.” J. Hydraul. Eng., 127(11), 969–978.
Information & Authors
Information
Published In
Copyright
© 2013 American Society of Civil Engineers.
History
Received: Sep 15, 2012
Accepted: Mar 21, 2013
Published online: Apr 1, 2013
Published in print: Sep 1, 2013
Discussion open until: Sep 1, 2013
Authors
Metrics & Citations
Metrics
Citations
Download citation
If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download.