An integrated seismic hazard framework for liquefaction triggering assessment of earthfill dams' foundation soils


Thesis Type: Postgraduate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Engineering, Department of Civil Engineering, Turkey

Approval Date: 2009

Student: SEVİNÇ ÜNSAL ORAL

Supervisor: KEMAL ÖNDER ÇETİN

Abstract:

Within the confines of this study, seismic soil liquefaction triggering potential of a dam foundation is assessed within an integrated probabilistic seismic hazard assessment framework. More specifically, the scheme presented hereby directly integrates effective stress-based seismic soil liquefaction triggering assessment with seismic hazard analysis framework, supported by an illustrative case. The proposed methodology successively, i) processes the discrete stages of probabilistic seismic hazard workflow upon seismic source characterization, ii) numerically develops the target elastic acceleration response spectra for typical rock sites, covering all the earthquake scenarios that are re-grouped with respect to earthquake magnitude and distance, iii) matches the strong ground motion records selected from a database with the target response spectra for every defined scenario, and iv) performs 2-D equivalent linear seismic response analyses of a 56 m high earth fill dam founded on 24 m thick alluvial deposits. Results of seismic response analyses are presented in the form of annual probability of excess pore pressure ratios and seismically-induced lateral deformations exceeding various threshold values. For the purpose of assessing the safety of the dam slopes, phi-c reduction based slope stability analyses were also performed representing post-liquefaction conditions. After having integrated this phi-c reduction analyses results into the probabilistic hazard framework, annual probabilities of factor of safety of slopes exceeding various threshold values were estimated. As the concluding remark, probability of liquefaction triggering, induced deformations and factor of safeties are presented for a service life of 100 years. It is believed that the proposed probabilistic seismic performance assessment methodology which incorporates both phi-c reduction based failure probabilities and seismic soil liquefaction-induced deformation potentials, provides dam engineers a robust methodology to rationally quantify the level of confidence with their decisions regarding if costly mitigation of dam foundation soils against seismic soil liquefaction triggering hazard and induced risks is necessary.