Prediction of earthquake-induced liquefaction for level and gently sloped ground

This paper presents a simplified procedure for predicting earthquake-induced level and sloped ground failure, namely liquefaction and shear failure. It consists of a framework where cyclic stress ratio (CSR), static stress ratio (SSR) and undrained shear strength (USS) are formulated considering simple shear conditions, which simulate field stress during earthquakes more realistically. The occurrence or not of ground failure is assessed by means of a plot ηmax (= [SSR+CSR]/USS) vs. ηmin (= [SSR-CSR]/USS), where a liquefaction zone, a shear failure zone and a safe zone (i.e. no-liquefaction and no-failure) are defined. Using this procedure, a soil column was examined and failure assessment was obtained for various soil elements, located at different depths beneath ground level. A total of 6 cases were generated by considering 2 slope inclination levels (i.e. i=0% and 5%) and 3 relative density states (i.e. Dr=25%, 50% and 75%). The 2012 Emilia Earthquake (Mw=5.9 and amax=0.26g), that produced an extensive liquefaction scenario in Northern Italy, was used as seismic input. For the case study examined, the prediction confirmed that soil was likely to experience severe liquefaction, except for the case of dense sand in level ground conditions. In addition, it clearly appears that gentle sloped conditions significantly decrease the resistance of soil against liquefaction. Based on past case histories, such a prediction is rational and, thus, the proposed procedure may represent a useful tool to assess earthquake-induced failure mechanisms for both level and sloped ground.