The Effect of Wave Action on Structures with Large Cracks

Damages of coastal structures are often wave induced. A new study revealed that wave impact generated pressures can travel into water filled cracks or joints, thus damaging or destroying the structure from within. A series of experiments was conducted in QUB's wave channel to assess the characteristics of breaking wave impact induced pressure pulse propagation through partially water filled cracks. It was found that the pressure pulses generally travel at very low velocities of 45–70 m/s within completely submerged cracks, whereas velocities in partially submerged cracks are significantly higher. Pulses attenuate fast inside the fully submerged crack, but slowly in partially submerged ones. 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 probably more dangerous man completely filled cracks. They are probably also the main cause for the seaward removal of blockwork in coastal engineering structures. This effect however is not limited to blockwork structures, but to every structure where cracks or joints occur, including natural rock cliffs.