Mele, Lucia (2020) Experimental and theoretical investigation on cyclic liquefaction mechanisms and on the effects of some mitigation measures. [Tesi di dottorato]

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Earthquakes are one of the most destructive natural phenomena, that hit several places in the world. These ground motions are also dangerous because of possible soil liquefaction phenomena. Liquefaction is a phenomenon marked by a rapid loss of shear strength and stiffness, which may occur in loose, saturated sandy soil deposits. The consequences may be catastrophic as demonstrated in several case histories. This thesis has been involved in the framework of LIQUEFACT project with the main purposes to better understand the mechanisms and the parameters that govern liquefaction phenomena and to study the possible mitigation techniques, providing guidelines and design tools for real applications in situ. As well-known, ground improvement is currently considered to be the most appropriate mitigation technique to prevent soil liquefaction. In this research, the effectiveness of some techniques (densification, addition of fine contents and desaturation) has been verified via experimental evidences coming from laboratory testing. Pros and cons of the studied liquefaction countermeasures have widely been discussed. Based on the experimental results performed on several sandy soils in different conditions, an insight on liquefaction mechanisms has been done. In particular, liquefaction phenomena have been widely studied starting from the trigger, passing from the parameters affecting liquefaction resistance, the behaviour of liquefied soils and concluding with the behaviour of re-consolidated soils, which experienced liquefaction. Experimental tests have been processed according to an energetic approach. Such approach have been applied to saturated and non-saturated soils, although the most important findings have been obtained for non-saturated soils, for which the energetic approach can be used also for predicting the cyclic resistance curves and then used as a simple design tool in desaturation interventions as countermeasure against liquefaction. To do that, an innovative synthetic state parameter, the specific volumetric energy to liquefaction (Ev,liq), has been introduced. The role of Ev,liq, together with the specific deviatoric energy to liquefaction (Es,liq) – which make up the specific total energy to reach liquefaction (Etot,liq) – has been investigated. In particular, the deviatoric component of specific energy to liquefaction has been used in the assessment of liquefaction potential of two case histories, whose results obtained according to the energetic-based approach have been compared with those of the stress-based approach. Although further tests are necessary to validate the energetic models of interpretation of liquefaction phenomena, the results shown in this research work seem to be very promising.

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