Rubble mound breakwaters play a crucial role in safeguarding coastlines and harbors, pro‎mp‎ting persistent research into their resilience against wave forces. Simultaneously, the poor quality of quarried stone in southern Iran, coupled with the advantages of multi-layered breakwaters in optimizing quarry resource utilization, underscores the substantial importance of investigating these structures. This study conducts a laboratory investigation with the objective of analyzing the influence of diverse environmental and geometric parameters on the stability of rubble mound structures, with a specific focus on a double-berm multi-layered berm breakwater configured as both a mono-berm and a double-berm arrangement. Experimental tests were conducted within a wave flume at Civil Engineering Department, Isfahan University of Technology, characterized by dimensions of 16 m in length, 1 m in height, and 0.8 min width under irregular waves. The study scrutinizes the impact of various environmental parameters, encompassing wave height, wave period, number of waves, water depth at the structure's toe, and diverse structural parameters including the nominal diameter of Class Ι stones, width of the first berm, height of Class Ι stones, and elevation of the first berm relative to the still water level. The primary focus is on the eroded area of the first berm in the presence of a second berm. Laboratory observations reveal that the introduction of a second berm triggers a transformation in wave breaking behavior from surging to plunging, subsequently altering the wave breaking location to a position farther from the first berm. This alteration contributes to a more stable configuration compared to the mono-berm structure. Additionally, the motion of stone particles on the slope of the structure contributes to its degradation. The strategic placement of a second berm at the toe of the structure serves to mitigate this effect by partially constraining wave run-up and run-down, consequently enhancing structural stability. Results from the experiments indicate that heightened wave height, extended wave periods, greater wave numbers, and increased water depth at the structure's toe increase the eroded area of the first berm, thereby diminishing structural stability. Moreover, enhancing the structural dimensions such as the width of the first berm, nominal diameter of Class Ι stones, and height of Class Ι stones enhances the stability of the double-berm multi-layered berm breakwater. Changing the elevation of the first berm relative to the still water level elicits distinct patterns in eroded area variations. In the context of higher wave combinations, the eroded area contracts, while in lower wave combinations, it expands. This phenomenon highlights a range for categorizing the structural behavior as partly or hardly reshaping performances. Furthermore, the study introduces the concept of an equivalent slope and subsequently the stability number to establish a unified relationship applicable to both mono-berm and double-berm multi-layered breakwaters. Ultimately, a comprehensive stability assessment equation is presented, addressing both surging and plunging wave breaking conditions.

محمدنويد مقيم

محمدرضا چمني , شهريار منصورزاده