Experimental study on the influence of water depth and bed slope variations on horizontal forces during the quasi-steady flow phase of dam break wave

Extreme coastal hazards, such as tsunamis, can cause significant damage to coastal structures. During surge impact on structures, the structure initially experiences surge wave impact pressures, whereas in the quasi-steady flow phase, it is predominantly subjected to quasi-hydrostatic pressure. However, real-world cases suggest that structural failure typically occurs during the quasi-steady flow phase. Therefore, this study conducted dam break wave impact experiments in a large-scale flume, considering the effects of upstream and downstream water depth ratios, bed slope, and channel length on the quasi-steady surge force. Based on the principles of mass and momentum conservation, a polynomial relationship between the water depth in front of the structure and the Froude number was derived and subsequently simplified to a linear form. Using experimental data, the linear relationship was optimally fitted using the least squares method, yielding the coefficients for the linear relationship under different slopes. This process led to the development of a computational model for the unit-width horizontal force F in front of the structure. The study shows that an increase in slope enhances the surge wave force, while an increase in water depth ratio and channel length reduces the intensity of the surge force. The surge wave moment increases nonlinearly with the Froude number, and the increase rate is reduced as the slope increases. Additionally, the surge moment exhibits a monotonic decrease with the increase in the water depth ratio.