Local scouring around perforated bridge abutments for non-cohesive soils

The effect of perforations on reduction of scouring at bridge abutments is studied experimentally. Different number of holes were placed through two different lengths of vertical wall abutments. Long term experiments were conducted to achieve the equilibrium scour hole condition. At the first stage, different arrangement of holes in horizontal and vertical rows were examined for maximum efficiency, that is maximum reduction of scour hole depth. Results showed that horizontal arrangements outperform the vertical ones with similar flow condition and opening ratio. At the next stage of experiments, the effect of relative abutment length that is the ratio of flow depth to abutment length on perforation efficiency was investigated. Results showed that in opening ratios smaller than 50%, the efficiency increased with increase in relative abutment length. Openings more than 50% did not affect the scour hole depth. Finally, by nonlinear regression analysis, an empirical equation was developed for estimating scour depth at abutments with the best arrangement of perforation.