Experimental study of the surge- and bore-induced impact pressure on a vertical wall and its foundation

Both surge and bore impacts could lead to the failure of coastal structures. Nevertheless, differences between the surge- and bore-induced hydrodynamic impact processes on a vertical wall are still unclear. Meanwhile, investigation of the bed pressure features during the wall impact is also rare. In this study, a series of dam-break experiments were conducted to specify the hydrodynamic characteristics of the surge and bore impact pressure on a vertical wall and its foundation. In the experiment, same initial water head was applied with five different initial downstream water levels (IDWLs). Temporal variations of the surge/bore impact pressures at four elevations on the wall and four positions along the bed were recorded. The surge induced maximum water height on the wall is larger than the bore induced one, which decreases with the increase of the IDWL. With the increase of the IDWL, the initial peak impact pressure gradually decays owing to the slowing down of flow velocity and the significant air entrainment at the bore front. Regarding the initial peak pressure and its rise time, it is confirmed that the initial surge impact pressure is sensitive to the wall elevation, whereas it is relatively uniform along the wall bottom region for the bore impact pressure. As for the measured bed pressure, the initial impact zone induced by the secondary flow near the wall and the falling impact zone caused by the falling down of water mass from the splash-ups away from the wall are identified, showing different hydrodynamic features.