The propagation of wave impact induced pressures into cracks and fissures

Rock cliffs and blockwork coastal structures often suffer a peculiar type of damage, whereby individual blocks are removed out of their location towards the sea. The location of damage suggests that breaking wave action is the main cause. It has been suggested that wave impact pressures travel into the water or air filled cracks and fissures of the structures, leading to large pressures acting inside of the structure or cliff and to the removal of blocks. This assumption was only recently confirmed for water filled cracks with a series of model tests at Queen's University Belfast. Real cracks in rock cliffs are, however, often only partially filled with water. A new experimental study, also conducted at Queen's University Belfast, revealed that wave impact generated pressures can ravel into both fully or partially water filled cracks or joints. In partially submerged cracks the pressure pulse was found to travel in the air, propagating fast and with little attenuation deep into the structure, signifying that partially filled cracks are potentially more dangerous for the integrity of the structure than completely water filled cracks. These pressure pulses may be the main cause for the seaward removal of blockwork in coastal engineering structures or of rock cliff material