Cyclic Failure of Fine-Grained Soils during the 1999 Kocaeli Earthquake

The 1999 Kocaeli earthquake caused severe damages, most notably in areas closer to the epicenter. Most of the major property damage resulted from liquefaction and cyclic failure. Many buildings settled and tilted due to the liquefaction and bearing capacity failures. Damages of loss of coastal lands and subsidence of the ground occurred at several sites along Izmit Bay due to liquefaction and cyclic failure. Several site surveys, soil investigations and static and dynamic laboratory soil tests were conducted covering most of the affected area. The results presented in this paper are part of an investigation including series of tests on the behavior of saturated natural fine-grained soil samples, taken from the area. The samples were tested using stress-controlled cyclic triaxial and cyclic torsional apparatuses. The results were analyzed for the assessment of dynamic instability of fine-grained soils by using the energy criteria, which is frequently used for liquefaction analysis. Analysis of cyclic test data suggests that portions of fine-grained soil deposits, i.e. silts and silty clays, likely developed relatively high excess pore pressures and significant shear strains during the earthquake that led to particle structure breakdown and strain softening, and thus, likely contributed to the observed overall stability problems.