Passeri, Federico

A blast-induced liquefaction test was conducted in the surroundings of Mirabello (NE Italy), where extensive liquefaction phenomena were observed after the 2012 Emilia earthquake. This experiment is the first blast-induced liquefaction test carried out in Italy. Several geophysical investigations were performed at the site to define initial soil condition and to evaluate the variations of the geophysical parameters over time. Specifically compressional (VP) and shear (VS) wave velocities were measured using both invasive (down-hole) and non-invasive (surface wave) tests. Electric Resistivity Tomography (ERT) tests were also carried out. Tests results before and after the blast-induced liquefaction are here presented and discussed with respect to the observed liquefaction effects. The evolution of measured geophysical parameters suggests that the soil modifications due to blasting (i.e., changes in porosity and soil structure) can be imaged with the adopted approaches.

Soil liquefaction can result in significant settlement and reduction of load-bearing capacity. Moreover, the generation of pore pressure during an earthquake and its post-seismic dissipation can generate permanent deformations and settlements. The quantitative evaluation of post-liquefaction settlements is of extreme importance for engineering purposes, i.e. for earthquake-resistant design of new buildings and safety evaluation of existing ones. Quantifying the extent of these phenomena is, however, rather difficult. Uncertainties arise from the stochastic nature of the earthquake loading, from the simplifications of soil models, and from the difficulty in establishing correlations between the pre-earthquake soil state and the post-seismic deformations. Field scale liquefaction tests, under controlled conditions, are therefore important for a correct quantification of these phenomena. Recent experiences (e.g. New Zealand, United States) show that liquefaction can be induced and monitored with field scale blast tests to study the related effects on soil geotechnical properties. Within this framework this paper introduces the preliminary results obtained from a research project on blast-induced liquefaction at field scale. Tests were performed at a trial site located in Mirabello (Ferrara, Italy), a village strongly affected by liquefaction phenomena during the 2012 Emilia Romagna earthquake. Invasive tests, such as piezocone, seismic dilatometer and down-hole tests, and non-invasive tests were carried out before and after the execution of two blast test sequences to study the variation in physical properties of the soils. Pore pressure transducers, settlement profilometers and accelerometers were installed with the objective of measuring, during and after the detonations, the generation and subsequent dissipation of the pore pressure, the vertical deformations, and the blast-induced ground motions respectively. Variations in load distribution on deep foundations due to soil liquefaction were also evaluated on a test micropile instrumented with a strain gauge array. Topographical surveys were carried out to measure ground surface settlements. Laboratory tests and trenches also provided increased understanding of the site characteristics.