The Effect of the Piles Cap Elevation on Local Scour around Complex Bridge Piers

Bridges are built to facilitate transportation between the two banks of the rivers and waterways. They are usually supported by piers with geometric shapes that differ from one bridge to another, such as a complex pier. Due to the intersection between bridge piers and water flow, many water vortices are generated, causing local scour around the bridge piers. Local scour around the complex piers is affected by many factors, including the geometry of the piers and other hydraulic factors. In this study, a number of laboratory experiments were conducted to investigate the effect of the pile cap elevation and water depth on local scour around complex pier piers using materials with a regular gradient and under the condition of sediment-free water flow. Eight ratios of the pile cap elevation to the cap thickness Z/Tpc were studied, ranging from -32% to 50%, and six different flow depths (y) between 10.5 cm and 18 cm. The results showed that the maximum scour depth was recorded to be 10.8 cm when the pile cap was partially covered with a sand bed (Z/TPC = 50%), the depth of scour increased with the increase in water depth up to 13.5 cm, then the effect of the increase in water depth was slight, although Increasing the intensity of the vortices due to the presence of the piles covering that prevent the impact of these vortices from reaching the soil surface.