Laura Tonni

Associate Professor

Department of Civil, Chemical, Environmental, and Materials Engineering

Academic discipline: ICAR/07 Geotechnics

Research

Keywords: Constitutive modelling Silts and silty sands Soil Liquefaction Cone penetration testing River embankment stability Underseepage and piping

Computational geomechanics. Research on this topic mainly consists in developping implicit algorithms for the integration of non-standard, advanced elastoplastic models, with special reference to Generalized Plasticity models. The numerical procedures are then used for solving boundary value problems relevant to geotechnical engineering. Applications are mainly concerned with the modelling of failure mechanisms of catastrophic landslides due to liquefaction phenomena in loose granular soil deposits.

Site characterization of intermediate soils (silts and silty sands) through piezocone tests. Research is based on a number of field studies carried out in intermediate deposits, including the Venetian Lagoon subsoil and other relevant deposits of the Po river valley. The study aims at developping reliable interpretation procedures of piezocone measurements in such soils, where standard and well-accepted empirical correlations seem to fail in providing good estimates of their mechanical parameters due to partial drainage phenomena around the advancing cone. Recent developments in this field have dealt with the estimate of liquefaction susceptibility of silty sands, based on the in-situ testing campaigns carried out in the Po river plain deposits within the research projects "Studio Teorico e sperimentale per la valutazione della suscettibilità alla liquefazione dei depositi sabbiosi: effetto delle condizioni stratigrafiche, dell'ambiente deposizionale e delle caratteristiche dell'azione sismica sull'innesco del fenomeno" (Bando ALMAIDEA 2017) e "Tecnologie innovative per la riduzione del rischio sismico delle costruzioni" (Bando POR-FESR 2014-2020, Project no. PG/2015/737636).

Constitutive modelling of sands and silty sands using a Generalized Plasticity approach. Theoretical modelling focuses on developing a new constitutive formulation for sands and silty sands, based on Generalized Plasticity premises in conjunction with the Critical State framework. The idea is to provide a simple and comprehensive formulation which allows unified modelling of granular soil behaviour over a wide range of densities and confining pressures, with special reference to the modelling of liquefaction and cyclic mobility.

Analysis of the geotechnical response of river embankments and assessment of their vulnerability. Research on this topic has been mainly developed in the context of a comprehensive research project promoted by the Po river basin Authority (AdBPo), with the aim of evaluating both the static and seismic stability of about 90 km of embankments in the middle-lower stretch of the Po river, including the municipalities with the highest seismic hazard. Detailed stratigraphic soil profiling as well as careful geotechnical characterization of the riverbank sediments and the surrounding subsoil have been carried out, mainly on the basis of in-situ tests. All geotechnical and geometrical parameters relevant to the outcome of the analyses have been modeled as random variables and stability analyses performed in terms of probability of failure. The main goal of the study is to provide a useful tool for the local Authority towards flooding risk assessment. More recently, attention has been focused on the analysis of piping phenomena, which turn out to be one of the most threatened collapse mechanisms for Po River embankments. A 3D finite element model of the groundwater flow within a specific segment of the Po River, affected by recurrent piping reactivations, has been developed with the aim of providing some insight into the most significant factors governing initiation of piping mechanism. Research on this topic also includes the development of effective low-impact engineering countermeasures against piping, as planned in the LIFE project LIFE19 ENV/IT/000071, "Natural-based solution to mitigate flood risk due to SAND BOILS reactivations along the Po River", funded by the European Commission within the LIFE Environment and Resource Efficiency Call. Laboratory physical modelling at both small-scale and medium-scale is currently underway.

In the context of riverbank stability, research activity has also dealt with the analysis of the seismic response of an irrigation canal riverbank (the Canale Diversivo di Burana), which was one of the most severely damaged structures by the seismic sequence that in May 2012 struck a large area of the Emilia-Romagna region, in Northern Italy. The study has been carried out in cooperation with researchers from various Italian Universities and technical experts of the Geological, Seismic and Soil Survey Regional Department. The main objectives of the analysis are: identification of the river bank seismic response during the 2012 earthquake, investigation of the damage causes, recommendation of remedial measures and seismic risk mitigation actions towards possible future earthquakes. To this purpose, a number of geotechnical investigations have been performed (in situ tests, geophysical investigations and laboratory tests) and an accurate geotechnical model for the seismic stability analyses has been thus defined. Potential liquefaction phenomena of the shallow sandy soils, in the foundation subsoil, have been taken into account in the analyses.

Laura Tonni

Research

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