Interlocking, rearrangement and progressive failure in rubble‑mound breakwaters

Rubble-mound breakwater stability is commonly assessed through Hudson- and Van der Meer-type empirical formulae, which relate wave loading, armour properties and geometry to global stability and damage parameters. These formulae remain the design basis, but they do not explicitly describe how inter-block contacts reorganise under repeated wave loading. A testable contact-network interpretation of progressive rubble-mound failure is developed here. The armour layer is treated as a granular assembly whose load-carrying capacity depends on the redundancy and persistence of load-bearing contacts. A normalised contact-network connectivity descriptor C N and an armour-motion descriptor A m are introduced as operational quantities for future laboratory, field or DEM/FEMDEM assessment. Four response regimes are distinguished: stable interlocking, cyclic reorganisation, local C N loss and cascading failure. A minimal two-variable description is used only to organise the hypotheses, not as a calibrated design model. The framework is compared with Iribarren-type damage descriptions and with existing 3D FEMDEM studies, and a concrete test protocol is proposed. The result is a complementary Perspective that links progressive breakwater damage to measurable changes in load-bearing contact state.