This paper presents a comprehensive geological and geotechnical study of the whole area affected by liquefaction following the 2012 Emilia earthquakes, including all the available information from the field reconnaissance surveys, in situ tests, and laboratory analyses. The compilation was performed at 120 liquefied sites to verify and validate the reliability of liquefaction charts in alluvial sediments, and to assess liquefaction induced by the 2012 seismic sequence in the Emilia plain. The results reveal a wide range of grain sizes (from clean sands to sandy silts) and compositional characteristics (quartz-rich to litharenitic) in the 2012 ejecta, and show a strong relationship between the liquefaction and stratigraphic architecture of the subsurface. The availability of in situ tests at the liquefied sites makes it possible to verify and validate the reliability of the liquefaction charts in alluvial sediments with respect to the real observations. For the analyzed Emilia case studies, the use of non-liquefiable crust provides better estimations of the liquefaction manifestations when coupled with the thickness of the liquefiable layer rather than with the liquefaction potential index. Altogether, this work makes available to the international scientific community a consistent liquefaction database for in-depth earthquake studies.

The composition and texture of liquefied sands represent an important tool for the recognition of buried source layers and for a better understanding of earthquake-induced liquefaction mechanisms. The earthquake-simulating field experiment (blast test) carried out in 2016 in fluvial sediments of the Emilia plain induced subsurface liquefaction and the surface expulsion of sand as sand blows. The area was widely affected by liquefaction phenomena during the Mw 6.1 Emilia earthquake (2012). The grain size and composition of sand blows ejected during the blast test have been compared with various horizons of buried fluvial sediments as deep as 20 m, and with sands from two trenches in the blast site representative of co-seismic 2012 liquefied sands. The sands from the cores show a clear trend from shallow lithoarenitic to deeper quartz–feldspar-rich compositions. The sands at shallow depth (up to 7.7 m) are the most lithoarenitic, with fine-grained sedimentary rock fragments (shales, siltstones, and limestone) as the dominant lithic type. Lithic fragments derive mostly from erosion of sedimentary terrigenous and carbonate successions of Apenninic affinity. In contrast, deeper sands (at depth > 7.7 m) are enriched in quartz and feldspars and impoverished in lithic fragments, which are similar in character to Po River sands. The composition of ejected sands largely overlap that of the shallow litharenitic Apenninic sands, indicating that liquefaction processes affected mainly sand layers at relatively shallow depth (5.9–7.7 m). Textural parameters show that silty sands and silts characterized by relatively high content of fines can also liquefy. This is in contrasts to most of the literature, where fine-grained sediments are considered as incapable of generating the high pore pressures commonly associated with liquefaction. This result should be considered when estimating the liquefaction as a potential hazard. Moreover, we observe that there is a selective loss of fines in the clastic dikes and sand volcanoes relative to the source beds, indicating that the liquefaction process appears to preferentially select the diameters of the grains that reach the ground surface, probably following the generated excess pore-water pressure. This may have caused the segregation and dispersion of the fine silt–clay content, producing highly sorted sand boils. This effect is easily observable in both the blast-induced sand boils, and the co-seismic 2012 dikes and sand boils ejected in the same area.

The dynamic cone penetration test (DPT) developed in China has been correlated with liquefaction resistance of gravelly soils based on field performance data from the ${\mathrm{M}}_{\mathrm{w}}7.9$ Wenchuan earthquake. With a diameter of 74 mm, DPT would be less sensitive to gravel size particles than the SPT or CPT and could be a viable assessment tool depending on gravel size and percentage. In this study, liquefaction resistance is evaluated using four DPT soundings with two hammer energies and shear wave velocity ($V_S$ ) measurements in Avasinis, Italy, where gravelly sand liquefied in the 1976 Friuli, Italy, earthquake. The DPT correctly predicted liquefaction at three sites where liquefaction was observed; however, it also predicted liquefaction in a highly stratified silt and silty gravel profile where ejecta was not observed. This failure appears to be a result of the “system response” of the profile, which impeded ejecta as identified at similar stratified sites in New Zealand. $V_{S1}$ -based triggering curves often predicted no liquefaction at sites where liquefaction was observed, suggesting that the boundary curves may need to shift to the right for gravelly soils. Standard SPT energy corrections were found to be reasonable for the DPT.