Collapse at the back sides of seawalls and quaywalls has occurred all over the world. This often stems from defects in caisson joints due to continued wave impacts causing internal erosion in the backfill sands. This study presents a new wave reduction method, called the Net Buffer Method, to reduce caisson joint waves for suppressing internal erosion and collapse of seawalls and quaywalls. Caisson joints may fail or widen due to the repeated action of waves that transmit though the joints. The new method, in which a net fiber material is installed within the joints, is capable of reducing such caisson joint waves by more than 80% in terms of the maximum and average wave pressures. Unlike previous countermeasures, it is applicable to joints of variable width and can autonomically adjust to changes in the configuration and surrounding environment due to continued wave impacts and other dynamic forcing such as earthquakes. Based on a three-year follow-up survey of its application, the proposed method has proven itself effective in suppressing the occurrence of re-collapse behind seawalls that repeatedly collapsed under severer wave loading. The proposed method is applicable to new, existing and aging caisson structures with joints of variable widths, and has indeed been adopted at seawalls/quaywalls designated as Major Ports and Strategic International Ports in Japan. It is therefore hoped that this new method will be utilized for disaster prevention/mitigation, a long service life and sustainable management of caisson-type seawalls, quaywalls and other such facilities.

Key Words: net buffer, caisson joint, collapse, internal erosion, wave