Liquefaction Analysis of Soils in the Western Izmit Basin, Turkey

Abstract

The Izmit Basin was formed as a result of activity on the North Anatolian Fault Zone (NAFZ). A Northern strand of the NAFZ crosses the basin in an east-west direction and is seismically active. Sand and silty sand deposits are widely spread across the alluvial basin. Groundwater levels vary between 1 m and 9.5 m below the land surface. Artificial Neural Network (ANN)– and Standard Penetration Test (SPT)–based liquefaction methods were used for soil liquefaction assessment. The ANN test session resulted in liquefaction prediction values from 0 to 1 for 46 samples. Twenty-nine samples with values greater than 0.8 were categorized as a high liquefaction prediction class. Two samples with values between 0.8 and 0.2 were categorized as a marginal liquefaction prediction class. Fifteen samples with values less than 0.2 were categorized as a low liquefaction prediction class. The SPT-based method evaluated 47 borings with coarse-grained soils for factor of safety (FS) against liquefaction and settlements and defined 37 borings with a FS value of less than 1. Overall total average settlement was calculated to be 5.4 cm. Coarse-grained soils with FS values of less than 1 were evaluated for liquefaction potential (PL) based on FS and depth of the soils. Calculations of PL resulted in very low (21 percent), low (64 percent), and high (15 percent) liquefaction potentials. The SPTbased results and ANN outputs were imported into ArcGIS to map the liquefaction resistance, seismic settlements, liquefaction potential, and liquefaction prediction for the study area.