V.S Ozgur Kirca - Faculty of Civil Engineering, Istanbul Technical University, Istanbul, Turkey
Giray Civak - Graduate School of Science, Engineering and Technology, Istanbul Technical University, Istanbul,Turkey
B Mutlu Sumer - BM Sumer Consultancy & Research, Istanbul, Turkey

Under cyclic loading conditions, shear deformations gradually rearrange soil grains and the pore water pressure increases in saturated, undrained soils at the expense of pore volume. In case of the presence of sufficient time and room, the pore water pressure reaches such a level that exceeds initial effective stresses and because of disappearing stresses between individual grains, the soil acts like a fluid, loses the ability to bear any load thus it fails. The term liquefaction is used to define this phenomenon in engineering terminology. Ithas been recognized that soils that can be liquefied under cyclic conditions are basically limited to fine soils or composite soils such as silty or clayey sands. As it was mentioned in the definition, liquefaction susceptibility is closely related with sort of soil parameters and cyclic loading conditions as expected. Through the years many soil failures caused byearthquake induced liquefaction has been reported by engineers and scientists. For example; in 1999 Kocaeli earthquake, an extensive liquefaction caused sinking ofbreakwaters, large displacements of quay walls and huge settlements of backfills which were resulted in serious damages to coastal structures (Figure 1). There are limited comprehensive analysis methods for earthquake induced seabed liquefaction and ordinarily, specially prepared charts where the dimensionless parameter Cyclic Stress Ratio (CSR) is plotted versus corrected SPT blow counts gathered from Standard Penetration Tests to define relative density of the soil have been used by practitioners to assess liquefactionsusceptibility, albeit as a first approximation [1].