Wave impact induced erosion of rock cliffs

Rock cliffs and blockwork coastal structures often suffer wave induced damages. A peculiar aspect of these damages is that the damages involve the seaward removal of individual blocks from blockwork structures, or the breaking off of large blocks of rock along fissure or crack lines inside the rock, leading to undercutting. The assumption that wave impact prcssures travel into water filled fissures, thus generating the damages, was only recently, confirmed at Queen’s University Belfast (QUB). An experimental study showed that wave impact pressures travel as compression waves into water filled cracks, whereby the pressure pulses rapidly decreased in magnitude. Real cracks in rock cliffs are however often only partially filled with water. A new experimental study, also conducted at QUB, revealed that wave impact generated pressures can travel into fully or partially waterfi 11 ed Cracksorjomts, thus damaging ordestroying the structure from within. In partially submerged cracks the pressure pulse was found to travel in the air, propagating fast and with little attenuation deep into the structure. This finding implies that partially filled cracks are probably more dangerous than completely filled cracks. The propagating pressure pulses may therefore be the main cause for the removal of blockwork in coastal engineering structures or of rock cliff material.