The issues of scouring around a bridge have become prominent in recent research mainly
due to recurrent extreme weather events. Thus, designing a bridge with the appropriate protection
measures is essential to safeguard it against failure, which may take place due to scouring from high
flows resulting from extreme weather events. Bridges may become partially or entirely submerged
during extreme weather events such as large floods and are subject to pressure-flow scour, a condition
where the flow is directed downward and under the bridge deck, creating an increase in flow velocity
and a corresponding increase in bed scour. This study aims to explore the pressure-flow scour depth
under a bridge deck without piers in the presence of two vertical wall abutments under clear water
experiments. Sixty-six tests were conducted involving the approach flow depth, bed material size,
contraction length, contraction width, and bridge opening for both pressure and free surface flow
conditions. An empirical equation was deduced to determine the maximum scour depth, which could
be applied as a preliminary design for bridges under pressure-flow conditions. The experimental
data were used to determine the performance of the earlier models of pressure-flow scour. The results
revealed that for pressure-flow conditions, the maximum scour depth increased by a factor between
2.15 and 9.81 times the maximum scour depth under free surface flow conditions. With same flow
depth, when the relative bridge length was increased from 5 to 7.5 and 7.5 to 10, the maximum scour
depth decreased by up to about 7.4% and 2.3%, respectively. When the relative bridge width was
decreased from 5.5 to 5.2 and 5.2 to 4.4, the maximum scour depth increased by up to about 45.6%
and 81.2%, respectively. |
