Dynamic Behaviour of Marine Sands Under Tsunami Induced Cyclic Loading: Laboratory Triaxial Testing

Abstract Among the effects induced by a major undersea earthquake are tsunamis, which impact not only coastal infrastructure, but also the seabed near port areas. The present study aims to experimentally characterize the impact of tsunamis on the dynamic response of the soil composing the seabed in port environments. A series of laboratory tests was carried out on samples of marine sand taken near the new quay (berth 24) of the Port of Béjaïa, located on the northeastern coast of Algeria. The specimens, prepared at two levels of relative density (Id = 0.25 and Id = 0.50) under undrained conditions, were subjected to dynamic characterization tests. The tests were conducted using a dynamic triaxial apparatus designed to simulate, under laboratory conditions, the cyclic loading effects of tsunami waves observed in the field, by varying both frequency and amplitude. The results show that the damping ratio (D) of the tested sand varies significantly depending on soil density and loading frequency. The secant shear modulus (Gs) is strongly influenced by the loading frequency for the low-density sand (Id = 0.25), while the higher-density sand (Id = 0.50) exhibits less sensitivity to these variations. Furthermore, the effect of soil density on the dynamic behaviour of the tested sand is more pronounced at low frequency but tends to become negligible at high frequency. These results highlight the critical influence of soil density and loading conditions on the dynamic response of marine soils subjected to cyclic stresses, such as those generated by a tsunami.