Probability-based Unified Liquefaction Triggering Models

Kemal Önder Çetin
Middle East Technical University, Turkey

The use of in-situ “index” testing continues to be the dominant approach in engineering practice for the assessment of seismic soil liquefaction triggering. The Standard Penetration Test (SPT), Cone Penetration Test (CPT), and shear wave velocity (Vs) – based seismic soil liquefaction case history databases are jointly used for the development of updated liquefaction triggering reliability-based models. Key elements in the development of these new correlations are: (1) accumulation of significantly expanded databases of field performance case histories, (2) use of improved knowledge and understanding of factors affecting interpretation of in-situ test data, (3) incorporation of improved understanding of factors affecting site-specific earthquake ground motions (including directivity effects, site-specific response, etc.), (4) use of improved methods for assessment of in-situ cyclic shear stress ratio (CSR), (5) screening of field data case histories on a quality/uncertainty basis, and (6) use of high-order probabilistic tools (Bayesian updating).  The resulting relationships not only provide greatly reduced uncertainty, they also help to resolve a number of corollary issues that have long been difficult and controversial including (i) magnitude-correlated duration weighting factors, (ii) adjustments for fines content, (iii) corrections for overburden stress and iv) geological setting and aging effects.