Experimental investigation of remediation techniques for enhancing the seismic performance of offshore caisson-type composite breakwaters on liquefiable seabed soils

Abstract

This study examines the failure mechanisms of offshore caisson-type composite breakwaters (OCCBs) under seismic loading through 1g shaking table model tests, comparing cases with and without remediation measures against seabed soil liquefaction. For this purpose, several countermeasures are implemented, comprising wraparound geogrid inclusions within the rubble mound layer, stone columns and compacted improvement zones in the seabed soil, all aimed at enhancing the seismic resilience and stability of OCCBs. Six physical model tests are conducted to evaluate the effectiveness of the applied remediation measures in minimizing liquefaction-induced deformations of OCCBs, including settlement, lateral movement, and tilting. Experimental findings indicate that the caisson settlement is primarily caused by the lateral flow of the foundation soil and the rubble mound layer. The combined use of stone columns and wraparound geogrid reinforcements efficiently mitigates this lateral flow. Notably, remediating just 2.8 % of the liquefiable seabed soil with stone columns decreases OCCB settlement and tilting by 45.4 % and 31 %, respectively, compared to the non-remediated model. Additionally, incorporating wraparound geogrid reinforcements within the rubble mound layer results in even further reductions of settlement and tilting by 90.6 % and 91.3 %, respectively. This research offers valuable insights for developing effective countermeasures to mitigate seismic-induced damage to OCCBs seated on liquefiable seabed soils.