Wave Damping Due to Liquefied Sandbed and Wave-Induced Compaction: Study on the Development of a Liquefied Sandbed Wave Barrier

A new wave absorbing system, called the liquefied sandbed wave barrier (LSWB) system, is currently under development at the Port and Harbour Research Institute (PHRI) of Japan. The wave damping effect by the LSWB system is substantial as confirmed by small-scale experiments and FEM numerical calculations, i.e., the wave transmission coefficient of the system is less than 0.2. Here, the results of large-scale experiments are discussed in view of practical application. Although the LSWB system provides high wave damping nearly equal to theoretical values, difficulty exists in obtaining a homogeneously liquefied sandbed due to the occurrence of liquefied sandbed compaction by cyclic wave loading, which in turn reduces excess pore pressure and the wave damping effect. These two phenomena primarily occur when the sandbed is made of fine sand having small permeability. Based on experimental results, we propose a design method including countermeasures against such problems and a prototype LSWB system is constructed in a very large wave flume at PHRI. Wave damping by the prototype LSWB system is confirmed to be quite stable and high as predicted by theoretical calculations.