Previous experimental research on the effects of debris on pier scour has focused primarily on circular and rectangular piers with debris present just under flow free surface. Debris-induced scour around sharp-nose piers, which are typical of masonry bridge piers, and the effect of debris elevation on pier scour have seldom been studied before. This paper aims to fill this knowledge gap. It presents results from flume experiments investigating scour around a sharp-nose pier under shallow flow conditions with angle of attack relative to the pier being zero. Uniform sand is used as bed material. Debris is modeled as stationary and extending only upstream of the pier. Three simplified debris geometries (cylinder, half-pyramid, and plate) are studied. Results show that scour depth decreases as debris gets closer to the bed with maximum scour depth occurring when debris is located just under the flow free surface. Interestingly, scour depths produced by debris in shallow flow are observed to be comparable to those produced by deep flow in the absence of debris. This finding highlights the importance of monitoring debris accumulation at bridges in nonflood conditions. Results also show that the volume of the scour hole around a pier increases quadratically with maximum scour depth. This information is useful for postflood scour remedial works. Lastly, the collected laboratory measurements are used to compare four popular equations for scour estimation on their ability to predict debris-induced scour. The Colorado State University (CSU) equation is found to offer the most accurate predictions. ; separate discussions must be submitted for individual papers. This paper is part of the Journal of Hydraulic Engineering, © ASCE, ISSN 0733-9429. © ASCE 04018071-1 J. Hydraul. Eng. J. Hydraul. Eng., 2018, 144(12): 04018071 Downloaded from ascelibrary.org by 44.224.250.200 on 07/05/20. Copyright ASCE. For personal use only; all rights reserved. © ASCE 04018071-2 J. Hydraul. Eng. J. Hydraul. Eng., 2018, 144(12): 04018071 Downloaded from ascelibrary.org by 44.224.250.200 on 07/05/20. Copyright ASCE. For personal use only; all rights reserved. © ASCE 04018071-5 J. Hydraul. Eng. J. Hydraul. Eng., 2018, 144(12): 04018071 Downloaded from ascelibrary.org by 44.224.250.200 on 07/05/20. Copyright ASCE. For personal use only; all rights reserved. © ASCE 04018071-6 J. Hydraul. Eng. J. Hydraul. Eng., 2018, 144(12): 04018071 Downloaded from ascelibrary.org by 44.224.250.200 on 07/05/20. Copyright ASCE. For personal use only; all rights reserved. © ASCE 04018071-8 J. Hydraul. Eng. J. Hydraul. Eng., 2018, 144(12): 04018071 Downloaded from ascelibrary.org by 44.224.250.200 on 07/05/20. Copyright ASCE. For personal use only; all rights reserved. © ASCE 04018071-10 J. Hydraul. Eng. J. Hydraul. Eng., 2018, 144(12): 04018071 Downloaded from ascelibrary.org by 44.224.250.200 on 07/05/20. Copyright ASCE. For personal use only; all rights reserved. © ASCE 04018071-12 J. Hydraul. Eng.
This paper describes the preliminary stage of an ongoing project investigating the hydrodynamic effects of debris blockage at masonry bridges. Debris blockage is cited as one of the primary causes of bridge failures in the UK and around the world. Masonry bridges, many of which are valuable historical assets, are particularly vulnerable to debris blockage due to their short spans and low clearance. This paper presents work done as part of the first phase of the project involving experimental research to understand the scientific relationships between debris characteristics and flow conditions. The study, being carried out at Centre for Water Systems at University of Exeter, utilizes a 0.6m-wide and 10m-long flume to run hydraulic experiments in order to characterize the impact of debris blockage on flow hydrodynamics, scour, and hydrodynamic pressures and forces at masonry bridges. This paper outlines the design of the experimental setup and the reasoning behind the choices for preliminary experimental parameters. The experiments are to include testing of bridge models and various 3D-printed debris shapes under realistic flow conditions. Geometry of the bridge and debris models are kept approximately similar to prototype conditions, with hydraulic conditions of the experiments designed to the degree that experimental constraints allow based on Froude similarity. Velocities, scour and hydrodynamic pressures are measured using an Acoustic Doppler Velocimeter, echo-sounding concept and pressure sensors, respectively. Preliminary results indicate that the designed experiments have the potential to enhance our understanding of the hydrodynamic effects of debris blockage.
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