Experimental Investigations of the Impact of Tsunami-Like Hydraulic Bores on a Square Vertical Structure. I: Pore Pressure Variations

A comprehensive experimental program was designed and conducted to investigate the effects of propagation of tsunami-like bores over a permeable surface, including the impacts on pore pressure variation around a square structure. A dam-break generation system was selected to model the tsunami-like bores and the effects of different impoundment depths were investigated to estimate pore pressure variations around a structural model. The latter was installed within a sand bed, and the hydraulic bores propagated over both horizontal and inclined surfaces as well as over dry and wet bed conditions. The latter involved the presence of a still-water layer over the sand bed. The transient variations of pore pressure distribution around the structure were measured, and their results were correlated with impoundment depth, still-water depth, and bed slope. A total of nine pore pressure tensiometers were installed on the front and side walls of the structure to record the time-history of pore pressure variation during bore propagation and subsequent impact onto the rigid structure for both sub- and supercritical bores. The magnitude of peak pore pressure and the time to reach peak pore pressure were found to be correlated with the still-to-impoundment depth ratio. It was found that effective peak pore pressure recorded on the side of the structural model was smaller and it occurred later in the supercritical bores compared with the subcritical bores. The contour plots of pore pressure in both front and side walls of the structural model were developed for a better understanding of the pore pressure distribution during the initial peak and the subsequent quasi-steady-state flow conditions. Experimental results indicate that the magnitude of pore pressure increased with increasing impoundment depth. Furthermore, pore pressure magnitude around the structure was considerably higher in the inclined bed tests, and they reached peak values faster than those observed for the horizontal bed tests. For both the horizontal and inclined bed tests, the front wall of the structural model exhibited larger pore pressure values than those observed on the side walls.