SIGNIFICANCE OF EARTHQUAKE-INDUCED DYNAMIC FORCES IN COASTAL STRUCTURES DESIGN

The dynamic forces of sea water and backfill soil acting on coastal em bankments and the hydrodynamic forces on offshore breakwaters have bee n analyzed using a finite-difference scheme. A non-horizontal sea bott om is considered in the analysis. Both rigid and flexible embankments are included in the study. For a coastal embankment, the hydrodynamic pressure of sea water acting on the embankment face significantly incr eases as the slope of the sea bottom increases. On the other side of t he embankment, the pore pressure and the interaction force between the soil and fluid will augment significantly when the backfill soil is c ompressed during earthquakes. When the sea-embankment-backfill soil in teraction is included, the dynamic forces acting on a flexible embankm ent are much larger than those on a rigid one. The comparison of evalu ating the sliding of a cassion in a case study of SPM by a conventiona l analysis and the present seismic analysis was made. The earthquake-i nduced dynamic pressures on both sides of the embankment (or breakwate r) could be much larger than the force generated by the storm surge. T he hydrodynamic (or seismic) analysis incorporating the effect of an e arthquake should be included in the coastal embankment or offshore bre akwater design, especially for the area with active earthquakes.