Experimental investigation of tsunami bore impact force and pressure on a square prism

• The vertical distribution of the bore induced pressure on the front wall of the structure was measured, at different orientations to the flow direction. In addition, the bore induced forces were measured at the base of the structure.
• For bores with fronts sloping at less than 15°, the maximum bore force on the structure is the sum of hydrostatic and hydrodynamic forces.
• Values of the total hydrodynamic forces after bore impact suggest drag coefficients ranging from 1.15 to 1.65 for the stream-wise force, for different orientations of the structure to the flow.
• For bores with fronts sloping at less than 15°, the upward force is due to buoyancy, and the hydrodynamic uplift force is negligible.

The 2004 Indian Ocean tsunami and the recent 2011 Japan tsunami have highlighted the need to investigate the interaction between tsunamis and coastal structures. Although some efforts have been made to determine tsunami loads on structures, there are discrepancies between the limited number of published design guidelines. This study comprises an experimental investigation of a tsunami bore interaction with an inland structure. Physical modelling of the tsunami bore in the laboratory allowed study of the impact of tsunami bores on a square prism model having different orientations to the flow direction. The use of common geometrical shapes simplifies experiments and increases the reliability of results. The experiments were conducted in a 14 m long, 1.2 m wide and 0.8 m deep wave flume equipped with an automatic gate designed to generate a tsunami bore. Measurements were made of the forces and pressures exerted on the model structure and of the bore heights and velocities. The vertical pressure distribution was measured on what was initially the structure's front wall, with the front wall at 0°, 30°, 45°, 60°, 90° and 135° to its original alignment. A relation between bore velocity and bore height is presented. The measured maximum forces in the stream-wise and upward directions were numerically modelled successfully, and relevant drag coefficients were determined for the structure at different orientations.