Assessment of liquefaction and lateral spreading on the shore of Lake Sapanca during the Kocaeli (Turkey) earthquake

The 1999 Kocaeli earthquake of Turkey (M_w = 7.4) caused great destruction to buildings, bridges and other facilities, and a death tall of about 20,000. During this earthquake, severe damages due to soil liquefaction and associated ground deformations also occurred widespread in the eastern Marmara Region of Turkey. Soil liquefaction was commonly observed along the shorelines. One of these typical sites is Sapanca town founded on the shore of Lake Sapanca. This study was undertaken as quantitative measurement of ground deformations induced by liquefaction along the southern shore of Lake Sapanca. The permanent lateral ground deformation was measured through the aerial photogrammetry technique at several locations both along the shoreline and in the town. In situ soil profiles and material properties at Sapanca area were obtained based on the data from 55 borings and standard penetration tests (SPT), and laboratory tests, respectively. The data and the empirical methods recommended by an NCEER workshop were employed to evaluate the liquefaction resistance of the soils. In addition, simple shaking tests on a limited number of samples were also performed. The permanent ground displacements were estimated from the existing empirical models, sliding block method and residual visco-elastic finite element methods. Then these estimations were compared with the observed ground displacements. The assessments suggested that liquefaction at Sapanca have occurred within Quaternary alluvial fan deposits at depths 1 and 14 m, and the major regions of liquefaction and associated ground deformations were located along the shore and creeks. The evaluations also indicated that for sites with no sand boils but with ground displacement greater than 1 m, thickness of the non-liquefiable layer was large. It is also noted that no liquefaction-induced ground surface disruption is expected at the site when the thickness of the liquefiable and non-liquefiable layers vary between 0.5 and 1.5 m, and 3.5 and 5.5 m, respectively. Except one model, all the empirical models employed in the study over-predicted the observed lateral ground displacements, while sliding block method and residual visco-elastic finite element methods yielded reasonably good results if the known properties of liquefied soils are used.