Breakwater is an important port engineering structure, and each country attach great importance to its safety. The preliminary design follows the specification or manual, and uses empirical formula and model test to verify its safety. However, the empirical formula in the current code considers the conventional structures under the positive action of waves, such as vertical structures or slope structures, and the wave direction is perpendicular to the structure strike. It is difficult to reflect the special structure of the joint section between vertical structure and slope structure. This kind of situation is the weak part of breakwater safety. The design code generally does not provide effective empirical formula. Once damage occurs, it will cause particularly serious consequences.

In this paper, a three–dimensional physical model test is used to study the stability of Breakwater at the junction of vertical faced section and rubble mounded sections. The bottom velocity in the convergence section are measured and compared with the open water area. Wave pressure distribution of the junction section is described. The physical model test indicated that bottom velocity at the junction section is similar with open area with downstream wave direction but rapidly larger with larger wave direction. Meanwhile, the wave pressure at junction section at low water level is larger than high water level, which is different finding from former thought of designers.


The breakwater is an important coastal structure to prevent waves. The design of coastal defences require the appropriate assessment of actions exerted by sea waves on the structure, such as wave force, run–up height, and current generated by waves. The wave forces can be characterized and quantified by physical and numerical modelling in addition to the application of semi–empirical formulations. Goda (1974, 1985) proposed the method to estimate the wave force on vertical breakwater by series of experiments. Then, Takahashi et al. (1994) improved Goda’s method by caisson slip tests. Goda’s method is adopted in the U.S. and Japan Standards (EM 1110-2-1100, Japan Standards). However, Goda’s method cannot consider the impact wave force. Allsop et al. (1996) noted that the impulsive pressure caused by wave breaking on to vertical wall may rise to 40 ρwgH (ρw is water density, g is gravity accelerate, H is wave height). Oumeraci et al. (1992) studied the impact pressure distribution, wave force, and overturning moments through large scale model tests. Allsop et al. (1996) proposed a formula to the impacting wave force under low mounds (0.3 < hb/hs < 0.6, where hb is the berm height and hs is the water depth in front of the wall), and noted that Goda’s formula could provide a conservative prediction of the horizontal wave force under high mounds (0.6 < hb/hs < 0.9). This formula was recommended by Oumeraci et al. (2001) and the U.K. Standards (2000). In practical engineering, the breakwater head is a vertical faced caisson, so the junction with the rubble mound requires special consideration as wave action can be concentrated here. Yu et al. (2003) and Li et al. (2008) analyzed the wave forces acting on vertical wall under oblique regular and irregular waves by experiments. They found that the maximum wave forces acting on unit length is often induced by oblique waves rather than normal waves. van Gent and van der Werf (2019) studied the interaction of oblique waves and rubble mounded breakwater by experimental tests. In the practice engineering, the breakwater head is usually designed as vertical faced section to widen the port entrance. Therefore, a junction section is needed to connect the vertical faced section and rubble mounded section. However, to the author knowledge, there is few research on the transitional section.

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