Full-scale experimental study on wave impacts at stepped revetments

Stepped revetments are known to be more effective in limiting wave overtopping and wave run-up than sloped revetments. However, literature on wave-induced impact pressures and comprehensive guidelines on the practical design for these structures is scarce. Laboratory experiments support the development of design recommendations. To date, studies for wave impacts at stepped revetments have mainly been carried out at small scales. This study characterizes wave-induced impact pressures at full scale, derives practical design formulae and evaluates findings against established methods for vertical walls and sloping structures. Additionally, an insight into the influence of scale is given by comparing wave impact characteristics for design cases between tests at multiple scales. Flume experiments with a slope of 1:3 and uniform step heights of 0.17 m and 0.50 m were investigated in the Large Wave Flume (GWK) in Hannover, Germany. Horizontal and vertical wave-induced pressure impacts were measured at 15 distinct locations for a large range of wave-breaking types (1.8 < ξ_m-1,0 < 2.8). Wave impact characteristics on stepped revetments align more closely with those observed on vertical walls than on sloped structures. Horizontal impacts are dominant over vertical impacts across the entire tested parameter range and thus critical for design considerations. Results show that previous small-scale tests significantly overestimate the maximum wave-induced impact pressures by a factor of 5.0 and maximum forces by a factor of 2.4. Impact loads occur significantly faster than at small scale. Design quasi-static pressures above the still-water level can be calculated and maximum horizontal impact pressures can be scaled using existing methods for vertical walls. Practical design formulae are derived for horizontal and vertical design pressures for different types of wave-breaking, for the vertical distribution of horizontal wave-induced impact pressures as well as for the temporal characteristics of these pressures at stepped revetments.