Scour around the single emergent cylinder due to subcritical and supercritical approach flow conditions

Flume experiments with a uniform cohesionless sand with d50=0.9mm were utilized in the current study to examine the local scour process around a single emergent cylinder under various geometrical circumstances and with a various flow characteristic that simulates an inundating tsunami flow. This single emergent cylinder represents a piloti-type column located over a movable bed material because piloti-type columns are used to elevate the building structures from the ground level. In the experiments, it was noted that the maximum scour depth probably occurs at the cylinder's upstream face, resembling local scour around a scaled-down bridge pier in an open channel. Additionally, the scour hole around the cylinder is shallower the smaller they are, as are the horseshoe vortices that surround them. Furthermore, the effects of the surface bow-wave, hydraulic jump detachment and the wall-jet over the front face of the emerging cylinder were used to identify the relationship concerning the scouring pattern and selected flow characteristics over a piloti-type emergent column under tsunami flow. Empirical formulae have been finally developed to determine the maximum scour depth in front of the cylinder, which is beneficial to characterize the stability of the piloti-type columns, considering the specified Froude number conditions.