Engineering Geological Characterization and Evaluation of Liquefaction Susceptibility of Foundation Soils at a Dam Site, Southwest Turkey

Abstract

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 alluvial deposits consisting of four soil zones. Under the ongoing dam site investigation stage a preliminary program of field and laboratory investigations was completed in 1995 to characterize soil properties and to evaluate the potential for liquefaction of the foundation soils during an earthquake. The results of both field and laboratory investigations 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 fines content, 51 layers were examined. From these, 17 layers through three boreholes along the centerline of the dam were considered for liquefaction assessment. Based on the seismic records available for the site vicinity, a scenario earthquake of M7.5, taking place 40 to 60 km from the site, was used in the analyses. Ground-motion attenuation relationships yield amax values between 0.12 g and 0.18 g . Two SPT-based methods 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 consequence of event two (amax = 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 recommended.