GNGTS 2018 - 37° Convegno Nazionale

668 GNGTS 2018 S essione 3.2 sections showed a good consistency between wells data and the common ERT sections of the two different campaigns (e.g. figure 2). - The virtual boreholes created from the geophysical sections, on which a 3 layers manual picking has been done, allowed to artificially correct clay thick. - Lastly, the geo-statistical analysis allowed to define the best interpolation scheme between data non-uniformly located on the studied area. Two interpolations were tested: kriging (Deutsch et al, 1998) and polynomial interpolation with Voxler®. We kept the 3d model produced via kriging which show more agreement according to the analysis of the variograms as input for the hydrological modelling. References Binley, A.: R3t version 1.8, Lancaster Univ., Lancaster, UK, available at: http://www.es.lancs.ac.uk/people/amb/ Freeware/ Freeware.htm., 2013. Deutsch, C. V., & Journel, A. G. (1998). Geostatistical software library and user’s guide. Oxford University Press, New York. Rücker, C., Günther, T., Wagner, F.M., 2017. pyGIMLi: An open-source library for modelling and inversion in geophysics, Computers and Geosciences, 109, 106-123, doi: 10.1016/j.cageo.2017.07.011 MICRO-ERT LABORATORY MEASUREMENTS FOR SEISMIC LIQUEFACTION R. Mollica 1,2 , R. de Franco 1 , G. Caielli 1 , G. Boniolo 1 , G.B. Crosta 2 , R. Castellanza 2 , A. Villa 2 , A. Motti 2 1 National Research Council – Institute for the Dynamics of Environmental Processes, Milan, Italy 2 University of Milan-Bicocca, Department of Earth and Environmental Sciences, Milan, Italy Liquefaction of soils is one of the most dangerous secondary effects of an earthquake. It deals with a drastic reduction of effective stresses and loss of bearing capacity in sandy, poorly consolidated, saturated soils. The rapid set-up of excess pore pressure (order of seconds) does not permit their dissipation and they increase until the critical point of liquefaction is reached. At this point, the saturated sandy system acts as a pressurized non-Newtonian fluid, which loses its shear strength and causes the fracturing of confining layers resulting in the typical liquefaction phenomena at the ground surface: sand boils, linear fractures, punctual uplift of sand, deformations and significant settlements. The liquefaction susceptibility is nowadays assessed by the so-called Simplified Approaches (Seed and Idriss, 1971; Robertson and Wride, 1998; Youd and Idriss, 2001; Boulanger and Idriss, 2014). These are based on in-situ geotechnical tests and in particular the Cone Penetration Test (CPT) and Standard Penetration Test (SPT), allow to evaluate by semi-empirical correlations a factor of safety (FS) given by the ratio between the Cyclic Resistance Ratio (CRR) and Cyclic Stress Ratio (CSR). The CSR is the load induced by a hypothetical earthquake, mainly depending on the local seismic hazard at the site, and the CRR is the soil resistance, which depends on the soil materials and their physico-mechanical properties. On the other hand, liquefaction susceptibility has not been well discussed from the point of view of geophysical parameters. The most important works on the subject are those of Hunter, (2003) and Ishihara and Tsukamoto, (2004) which stress the importance of measuring P and S waves in order to characterize soils prone to liquefaction. By following these studies, de Franco et al. (2018), suggests a first approach to attain the geophysical susceptibility to liquefaction. They demonstrate that it is possible to identify soils prone to liquefaction by measuring their seismic velocities ( v p and v s ): the first one acts as a proxy of the degree of water saturation and the second one as a proxy of the geotechnical soil class.