Liquefaction potential evaluation of the quaternary alluvium, Western Ankara (Turkey)

Abstract

Liquefaction of the soils is a major problem during and after earthquakes, and can lead to severe damage. A wide range of experience in dealing with natural hazards was gained in the capital city of Ankara after several earthquakes occured in Kaman (1938), Gerede (1944), and Duzce (1999), and in later events. The recent findings after the Orta (2000) and Bala (2005, 2007) earthquakes proved that Ankara should not be designated as a nonseismic hazard zone, as it has been previously. The Quaternary age alluvium is located in the nearby suburbs of Etimesgut, Macunkoy, Cuglu, Avdan, and Kazan. A high density of population and structures is spread over this alluvium, which contains a high percentage of cohesive soils associated with sand and gravel lenses. The depths of the groundwater level ranges between 6.0 and 8.0 m in west Etimesgut, 3.0 m in Macunkoy, 5.0 to 7.0–8.0 m in Cuglu/Avdan, and 4.5–7.0 m in southern Kazan. The average S wave velocities of the alluvium derived from the ReMi were 140 m/s in Etimesgut, 200 m/s in Macunkoy, 134 m/s in Cuglu/Avdan, and 200 m/s in Kazan, respectively. Liquefaction evaluation is conducted by standard penetration blow count, shear wave velocity, and threshold acceleration. Varying horizontal accelerations of the input motions in the soil stratigraphy were generated via the Quad4m program. Geotechnical investigation and proper soil improvement should be carried out in order to prevent structural damage.