Differences between mechanical and electrical cone penetration test in the liquefaction hazard assessment and soil profile reconstruction

Abstract

Liquefaction - hazard assessment is often accomplished by means of simplified procedures, which are based on CPT. The CPT liquefaction procedures, generally, require cone penetration test with electrical tip or the measure of u (CPTu); however, in most countries, as Italy, penetrometric tests are carried out with mechanical tip (CPTm). Generally, CPTm leads to an estimate of the Liquefaction Potential lower than that inferred from CPTu. Moreover, CPTm has a reduced resolution in soil profiling. While the cone – shape effects on qc are not very relevant, those on fs can strongly influence the FSL calculation, especially in the case of silty sands. Within this framework, the main aim of this work is to identify the differences in liquefaction - hazard evaluation and soil profile interpretation in pairs of CPTm/CPTu. After that, two methodologies were used to correct CPTm results. At first, it was developed an empirical correlation between the sleeve friction measured with CPTm and that measured with electrical CPT/CPTu. After that, a method developed in literature was applied to the same CPTm/CPTu pairs. The two corrections were compared in order to see which one led to the best results in terms of enhancement of the liquefaction hazard assessment and soil profile reconstruction. Tests have been carried out in the area interested by the 2012 Emilia earthquake (Italy)