ENGINEERING GEOLOGICAL CHARACTERIZATION AND EVALUATION OF LIQUEFACTION SUSCEPTIBILITY OF FOUNDATION SOILS AT A DAM SITE, SOUTHWEST TURKEY

Osmankalfalar Dam was planned to be built in the Mediterranean region of Turkey. The 29.5 m high-zoned embankment dam will be founded on all uvial deposits consisting of four soil zones. Under the ongoing dam si te investigation stage a preliminary program of field and laboratory i nvestigations was completed in 1995 to characterize soil properties an d to evaluate the potential for liquefaction of the foundation soils d uring an earthquake. The results of both field and laboratory investig ations that were used to assess the ground conditions, with particular reference to the liquefaction susceptibility-at the proposed dam site , is presented. Considering the limitations in SPT blow-count and fine s content, 51 layers were examined. From these, 17 layers through thre e boreholes along the centerline of the dam were considered for liquef action assessment. Based on the seismic records available for the site vicinity, a scenario earthquake of M7.5, taking place 40 to 60 km fro m the site, was used in the analyses. Ground-motion attenuation relati onships yield a(max) values between 0.12 g and 0.18 g, Two SPT-based m ethods were evaluated and the results derived from these were compared to those obtained from laboratory cyclic triaxial tests performed on tube samples from trial pits. The methods revealed that silty fine-to- medium sand layers between the depths of 8 and 15 m in zone B would be susceptible and marginally susceptible to liquefaction as a consequen ce of event two (a(max) = 0.18 g) during the operational stage of the dam. Necessary future investigations and possible remedial measures to increase liquefaction resistance of the foundation soils were recomme nded.