Scour and hydrodynamic effects of debris blockage at masonry bridges: insights from experimental and numerical modelling

Abstract

This paper describes preliminary results of a project investigating the scour and hydrodynamic effects of debris blockage at masonry bridges. Debris blockage, which is often cited as one of the primary causes of bridge failures in the UK and around the world, results in a larger obstruction to the flow leading to increased flow velocities, scour and hydrodynamic forces, compared to the conditions without debris. This, in turn, can affect the structural stability of bridges, for example, by undermining their foundations. Masonry bridges, many of which are valuable historical assets, are particularly vulnerable to debris blockage due to their short spans and low clearance. The reported study, being undertaken at the Centre for Water Systems at the University of Exeter, has two main phases: (i) laboratory experiments and (ii) CFD simulations. In the first phase, a 0.6m-wide and 10m-long flume is utilized to study the flow hydrodynamics and scour associated with pier/bridge models in several reference scenarios. The geometry of the pier/bridge and debris models are kept approximately similar to prototype conditions, with hydraulic conditions of the experiments designed to the degree that laboratory constraints allow to maintain Froude similarity. Velocities and scour are measured via an acoustic Doppler velocimeter and echo-sounding concept. Experimental results are used to calibrate and validate CFD models which can later enable simulation of more complicated scenarios. This paper will report these preliminary results from both experimental and CFD phases. Preliminary experimental results highlight the significance of debris existence in enhancing scour due to increasing flow downward velocities. Preliminary results from CFD modelling also show good agreement with experimental results.