Hydraulic stability of rock armors in breaking wave conditions

Abstract

Armor layers of mound breakwaters are usually designed with empirical formulas based on small-scale tests in non-breaking wave conditions. However, most rubble mound breakwaters are constructed in the depth-induced breaking zone, where they must withstand design storms having some percentage of large waves breaking before reaching the structure; in these cases, the design formulas for non-breaking wave conditions are not fully valid. To characterize double-layer rock armor damage in breaking wave conditions, 2D physical model tests were carried out with a bottom slope m=1/50. In order to develop a simple method to determine the wave parameters in the depth-induced breaking zone, experimental wave measurements were compared to the numerical estimations given by the SwanOne model. An analysis was conducted to select the best characteristic wave height to estimate rock armor damage when dealing with depth-induced breaking waves; the spectral significant wave height, H m0 , estimated at a distance of 3h s seaward from the structure toe, was found to be the most adequate. 2 A new hydraulic stability formula is proposed for double-layer rock armors in breaking wave conditions, considering the observed potential 6-power relationship between the equivalent dimensionless armor damage and the H m0 at 3h s seaward distance from the structure toe.

Influence of Mild Bottom Slopes on the Overtopping Flow over Mound Breakwaters under Depth-Limited Breaking Wave Conditions

“…Therefore, when reflection is small (K r < 0.4), the incident significant wave height obtained from the K r measured in the wave generation zone is a good estimator of the actual incident significant wave height. This result agrees with those reported in [10] and [17]. However, as those authors [17] pointed out, measurements without a structure are more reliable when estimating incident waves, and they were the ones used for the following analysis.…”

“…However, the bottom slope (m) has a significant influence on the type of wave breaking at the toe of the structure. Herrera et al [10] pointed out that the bottom slope plays an important role in mound breakwater design; in depth-limited breaking-wave conditions, the optimum point where wave characteristics are estimated is relevant for design and needs to be determined. This research focuses on the bottom slope influence on OLT and OFV during extreme overtopping events on mound breakwaters under depth-limited breaking-wave conditions.…”

“…Waves were analyzed following the methodology for depth-limited breaking waves proposed by Herrera and Medina [17] and Herrera et al [10], and similar validations to those proposed by the authors were conducted. Note that this methodology is applicable when reflection is relevant but not dominant (reflection coefficient K r = H s,r /H s,i < 0.4, where H s,r and H s,i are the reflected and incident spectral significant wave height, respectively).…”

“…Thus, a distance of 3h s from the model toe was selected as the optimum zone to estimate H s for the calculation of h c,2% (B/2) and u c,2% (B/2). This point was also selected by Herrera et al [10] to better describe the hydraulic stability of rock-armored rubble mound breakwaters in depth-limited wave conditions. This distance approximately corresponds to the distance of 5H s proposed by Goda [29] and recommended by Melby [30] to determine wave parameters, when considering H s in breaking wave conditions for vertical breakwaters.…”

Analysis of the Power Plant Breakwater Failure Subjected to Typhoon Mangkhut Based on Model Experiment

“…Therefore, the armor design in wave breaking conditions involves estimating the incident characteristic wave height at the breakwater toe, but the standard stability formulas found in the literature have rarely taken into account the wave height distribution changes due to wave breaking. Some empirical modifications have been proposed by Herrera et al [5] to estimate rock armor damage in breaking wave conditions. However, the hydraulic stability formula developed by Herrera et al [5] is only valid for frontal slope armor with zero or low overtopping rates.…”