A study on the effects of debris accumulation at sacrificial piles on bridge pier scour: II. Empirical formula

The major damage of bridges at river crossing occurs during floods. Damage is caused for various reasons, the main reason being riverbed scour at bridge foundations, namely pier and abutments. Debris accumulation at bridge pier provides larger obstruction to flow than an isolated bridge pier. The presence of debris causes larger scours and sediment removal compared to the absence of debris accumulation. Debris accumulation at bridge pier effects to bridge pier scour has been studied by several researchers. But the effects of debris accumulation at sacrificial piles on bridge pier scour have not been studied, yet. The aim of this study is to estimates the effects of debris accumulated at sacrificial piles to bridge pier scour and proposes a new formula for predicting bridge pier scour depth with debris accumulated at the sacrificial piles. Experiments were performed to understand the changes and interaction of scour depth over a range of flow depths, y and flow intensities, V/Vc. Experiments were conducted in single pier scour, sacrificial piles scour, single pier with debris scour and sacrificial piles with debris scour. By comparing each of the experimental results it has been found that debris effects to bridge pier scour related to its size and thickness. Several scour depth prediction methods were compared with the results of this experimental study results. Among those formulae Melville’s formula was chosen to modify. The proposed modified Melville’s formula depth-size factor, Kyb′= 1.56D was defined in this study. A new relation has been proposed to predict the effects of debris accumulation at sacrificial piles on bridge pier scour in term of relative maximum scour depth. De′ is proposed as effective pier with debris accumulated at sacrificial piles. The new proposed formula is well fitted with the experimental results. The results of experiments from the previous paper are used to analyze and the new formula is proposed.