Influence of Finite-Length Seawalls for Tsunami Loading on Coastal Structures

This paper presents new experimental data and predictive equations for the reduction of the tsunami inundation force provided by finite-length seawalls. The hydraulic model experiments were conducted in a rectangular basin equipped with a large-stroke piston-type wavemaker to produce a transient pulse on the basis of an error function to best simulate the initial phases of tsunami inundation. The bathymetry had a mild slope constant in the cross-shore direction and was followed by a flat section raised above the mean water line. The tsunami force, pressure, and run-up were measured on an instrumented specimen located on the flat section, and a seawall was placed between the specimen and the shoreline. The incident wave conditions, seawall positions, and seawall heights were varied systematically to quantify the reduction of the maximum and average force relative to the baseline conditions without a seawall. Reduction factors ranged from 1.0 (no reduction) to 0.10 (90% reduction). Two empirical formulas were derived to predict the reduction factors for the maximum and average force using as input the incident (unbroken) tsunami height, the bore height at the seawall (in the absence of the wall), the seawall height, and the position of the seawall relative to the shoreline and design structure. The equations predicted the data for which they were calibrated with $R^2$ values of 0.86 and 0.83 for the maximum and average forces, respectively. The equations were used to predict two other laboratory data sets: one conducted in the same facility under the same conditions with the specimen replaced by a column-supported structure, and a second, previous study in a two-dimensional wave flume at larger scale.