Effects of gradation on the long-shore transport processes and reshaping of rubble mound breakwaters under construction exposed to head-on and oblique waves

•The reshaping mechanisms of both trunks and roundheads of rubble mound breakwaters under construction are analysed.•The effects of the material grading, the wave load and obliquity are investigated.•Trunk reshaping can be described through the same key parameters defined in the literature for berm breakwaters.•The effect of grading appears to be the most significant, with a wider grading leading to longer crest and step lengths.•The results can be used for optimising the selection of the fractions and volumes of the construction materials.

Breakwaters under construction are prone to undesired reshaping because their core is not designed to withstand severe or moderate wave loads. While the reshaping of a finished breakwater was subject of comprehensive research, few studies dealt specifically with the reshaping mechanisms of a breakwater under construction, i.e. of the breakwater core. This paper presents a set of experimental tests focused on the reshaping of rubble mound breakwater trunks and roundheads undergone during the construction phase. The study accounts for oblique wave attacks and grading of the construction material. Better insights on how and how far such reshaping takes place are derived in the perspective of providing coastal designers and constructors with valuable information for optimising the selection of the fractions and volumes of the construction materials and for taking into account potential damages within the construction schedule and therefore additional costs.