Scour around Bridge Piers: Numerical Investigations of the Longitudinal Biconcave Pier Shape

Abdelali Seddini,Abderrahmane Nekkache Ghenim,Bouabdellah Guemou

doi:10.3311/ppme.12263

Abdelali Seddini, Abderrahmane Nekkache Ghenim + Show 1 more

Open Access

https://doi.org/10.3311/ppme.12263

Copy DOI

Abstract

The flow pattern around a bridge pier and the scouring phenomenon are very complicated. The basic mechanism causing local scour is the down-flow at the upstream face of the pier. It is understood that the horseshoe vortex is the key mechanism that leads to the local scour around pier; existing literature revealed that the strength of the down-flow, horseshoe vortex and the wake vortex are greater in the case of square piers compared to circular piers. In this paper we have investigated a new longitudinal biconcave bridge pier shape that reduces better the bed shear stress. For that purpose, a number of numerical simulations have been carried out using a Finite Volume Method (FVM) and for the turbulence model we have chosen the Detached Eddy Simulation (DES) for its capability to capture the rich dynamics of the horseshoe vortex at the upstream junction between the pier and the bed.The present study shows that the new longitudinal biconcave bridge pier shape reduces 10 % to 12 % the bed shear stress at the junction between the pier and the bed in other hand this shape increases the bed shear stress about 20 % but at a distance of D downstream the bridge pier in the flow direction.

Highlights

When a pile is placed in an erodible bed, scour phenomena will take place around it, due to the action of waves and currents
Existent bridges need to be protected against scour, we have discussed a new geometric alternative that may reduce the bed shear stress, and we proposed an alternative for the longitudinal shape of the bridge pier
In this paper we focus on the bed shear stress because the launching of the scour is linked to this factor, for this purpose we have run numerical simulations we have compared the velocity profiles and the bed shear stress for all configurations

Summary

Introduction

When a pile is placed in an erodible bed, scour phenomena will take place around it, due to the action of waves and currents. The pile scour is a complex process, in which the main element is the horseshoe vortex [1]. It causes an increase in local sediment transport capacity and this leads to scour in the vicinity of the structure, this is referred to as local scour in literature (Fig. 1). Local scour has been identified as one of the key factors that cause failures of structures in bridge engineering, coastal and offshore engineering. As reported in the literature, a series of relatively recent bridge failures because of pier scour [3], and over the last 30 years in the United States, one thousand bridges have collapsed because of hydraulic failure [4]

Objectives

Results

Conclusion