Empirical correlations to improve the use of mechanical CPT in the liquefaction potential evaluation and soil profile reconstruction

CPT-based simplified methods are the common used approaches to determine the liquefaction hazard and they require cone penetration test with electrical tip. However, in some countries, as Italy, penetrometric tests are carried out with mechanical tip (CPTm). The cone-shape effects on sleeve friction (fs) have the greatest influence on soil classification in terms of SBT, underestimating the grain size of loose soils (e.g. sands) with respect to CPTu. An empirical correlation between the fs measured with CPTm and CPTu was tested. Moreover, another correlation was developed to determine a ΔIc value as function of the cone resistance in the case of silty sands and sandy silts non correctly identified by the SBT classification systems. The correlation was applied to tests carried out in the area interested by the 2012 Emilia earthquake (Italy), where liquefaction phenomena have occurred. The procedure makes possible to use huge existing database (CPTm) for liquefaction risk assessment.