Guido Gottardi

• PhD Geotechnical Engineering
• Professor (Full) at University of Bologna

In May 2023, two extreme weather events struck Emilia- Romagna, followed by two more in late 2024, indicating an increasing frequency likely linked to climate change. This study examines embankment breaches from the May 2023 floods to develop interpretative models of failure mechanisms based on field data and eyewitness accounts. The observed failu...

Il meccanismo di collasso arginale per erosione retrogressiva da sottofiltrazione (Backward Erosion Piping-BEP) rappresenta una minaccia significativa per le strutture di difesa idraulica caratterizzate da fondazioni di natura granulare, anche confinate superiormente da depositi più fini. Questa configurazione stratigrafica è ampiamente documentata...

La presenza dei fontanazzi lungo gli argini fluviali, ossia di zone di fuoriuscita di sabbia fluidificata che si accumula sul piano campagna, rappresenta il tipico indizio dell’innesco e della progressione di un processo noto come “erosione retrogressiva per sottofiltrazione”. Il fenomeno, caratterizzato dalla formazione di piccoli canali che dal p...

Due to continuous water level fluctuations and changes in climatic boundary conditions, river embankments experience frequent variations in the degree of saturation and suction distributions, which strongly influence earthworks performance, both in terms of infiltration regime and stability conditions. For these reasons, an experimental campaign ai...

In the present context of climate change, the frequency of floods has increased, and their consequences are exacerbated by growing urbanization. Consequently, river embankments are recognized as strategic structures, crucial for safeguarding human activities against flood events and for the virtuous management of territories. Given their significan...

River floods rank among the most significant natural hazard in Europe, causing substantial economic and human losses and are frequently due to severe damages endured by water retaining earthworks, under extreme weather events. In this framework, a reliable assessment of the existing river embankments safety conditions, represents a key aspect to en...

The city of Ravenna (Italy) is worldwide famous for the well-preserved late Roman and Byzantine architecture with eight buildings protected by UNESCO as part of the World Heritage Site “Early Christian Monuments of Ravenna”. Climate change effects have increased the site vulnerability to natural hazards, in particular flooding and subsidence, two p...

Backward erosion piping (BEP) is an internal erosion process that may develop as a consequence of seepage processes through the aquifers underneath river embankment structures. This phenomenon can be identified in the field by observing the formation of sand boils on the ground surface at or near the embankment toe. Along the Po River, more than 13...

Backward erosion piping (BEP) is a phenomenon that can develop in the subsoils of river embankments during intense flood events, manifesting at the ground level as emerging sand boils. This process affects more than 130 sections of the Po river main embankments and many major streams in Europe and worldwide. This contribution aims to illustrate the...

This contribution describes the methodology adopted for the systematic collection of data on the main breaches experienced by the embankment systems affected by the exceptional flood events occurred in May 2023 in Emilia-Romagna. To this purpose, all main observed failures and their characteristics have been catalogued and extensive visual evidence...

Sommario L'erosione retrogressiva nei terreni di fondazione (backward erosion piping) degli argini fluviali è un fenomeno che può svilupparsi in concomitanza di intensi eventi di piena e che si manifesta con la formazione dei 'fontanazzi', in corrispondenza del piano campagna. Tale processo interessa numerosi tratti degli argini maestri del fiume P...

The accurate characterization of the transient water flow through unsaturated domains requires a precise knowledge of model parameters that govern the complex interactions of soil and fluid properties with boundary conditions. Inverse Analysis, a powerful computational technique, has emerged as a cornerstone in the process of estimating these param...

The paper summarises the main findings of a parametric numerical investigation focusing on the seismic response of the foundation soil below the Two Towers, the historic medieval symbol of Bologna (Italy), dated back to the XII century. The fine-grained strata were recently characterised by an experimental field campaign down to 40 m below the grou...

Uncertainty in the measurement of the cone penetration test with pore-water pressure measurement (i.e. piezocone testing CPTU) can be caused by an equipment malfunction, poor calibration and maintenance of sensors, but also by a lack of saturation of the piezocone. The standards allow for many different options in terms of filters, saturation fluid...

The city of Ravenna, in northern Italy, is worldwide famous for the well-preserved late Roman and Byzantine architectures characterized by fabulous mosaics that have earned the UNESCO World Heritage status. The constantly growing attention towards their conservation has promoted research activities that focus on the effect of the considerable cumul...

The design and vulnerability assessment of earth-filled water retaining structures require the elaboration of reliable seepage analyses. Model predictions, however, can result highly unreliable because of poor parameter estimations. To address this issue, inverse modelling techniques can be implemented, incorporating observations of ongoing process...

River embankments are designed to face hydraulic actions produced by river level fluctuations. Breach occurrence on these earth structures could be driven by various factors, all possibly concurring in the collapse during an extreme event. Among the possible mechanisms that may lead the structure to failure, the onset and progression of erosion phe...

Due to the increasingly frequent occurrence of extreme events related to climate change, the in-depth study of exceptional rainfall and flooding on earthen structures is essential. In particular, the associated consequences in terms of economic and human losses have caused the urgency of developing forecasting tools that can ensure a proper evaluat...

The city of Ravenna, in northern Italy, is worldwide famous for the well-preserved late Roman and Byzantine architectures characterized by fabulous mosaics that have earned the UNESCO World Heritage status. The constantly growing attention towards their conservation has promoted research activities that focus on the effect of the considerable cumul...

The design and vulnerability assessment of earth-filled water retaining structures require the elaboration of reliable seepage analyses. Model predictions, however, can result highly unreliable because of poor parameter estimations. To address this issue, inverse modelling techniques can be implemented, incorporating observations of on-going proces...

The stability of slopes is greatly influenced by seasonal variations in pore water pressures induced by rainfall infiltration and evapo-transpiration processes. An accurate prediction of the hydrological effects of long-stem planting is highly relevant in the risk assessment of slopes failure, but it is often strongly simplified or even neglected...

Woody plants on earthen slopes are a bioengineering solution for the prevention of shallow landslides that occur mostly during a wet season. From a soil-hydrological point of view, slope stability is influenced by plant roots reducing soil water content through transpiration. Despite this, conventional engineering practice tends to ignore the effec...

Woody plants on earthen slopes are a bioengineering solution for the prevention of shallow landslides that occur mostly during a wet season. From a soil-hydrological point of view, slope stability is influenced by plant roots reducing soil water content through transpiration. Despite this, conventional engineering practice tends to ignore the effec...

Earthen river embankments are typically in unsaturated conditions during their lifetime and the degree of saturation within their bodies may vary significantly throughout the year, due to seasonalfluctuations of the river stage, as well as infiltrations of meteoric precipitation and evapotranspiration phenomena. Given the significant effects of par...

The paper deals with subsidence and flooding risks associated to the Archaeological Site of Santa Croce, encompassing a 5th century church together with the remains of a Roman domus and its mosaics, located in the centre of the historic town of Ravenna (Italy). A geotechnical field campaign and the installation of a new piezometer monitoring system...

Extreme geohazards, such as flood events, are becoming increasingly frequent due to the major impact of climate change, with severe consequences in terms of economic damage and loss of human. Water retaining earthworks play a key role in the preservation of the built and rural environment, thus a reliable assessment of river embankment safety condi...

Italian experiences provide a long list of successful engineering solutions for the preservation of historic sites and, in particular, of tall structures like medieval and bell towers. Among them, Pisa Tower and Frari Bell Tower in Venice can demonstrate that innovative approaches and methodologies for the strengthening of historic foundations can...

River embankments are designed to face hydraulic actions produced by river level fluctuations. Breach occurrence on these earth structures could be driven by various factors, all possibly concurring in the collapse during an extreme event. Among the possible mechanisms that may lead the structure to failure , the onset and progression of erosion ph...

Seepage in the vadose zone greatly depends on the hydraulic properties of the soil. Their experimental determination often requires specific equipment and time-consuming procedures; furthermore, in many applications, such as river embankments, the spatial variability of these properties turns out to be particularly significant. Although the use of...

Evapotranspiration is a crucial phenomenon for the hydrological balance of the vadose zone; its evaluation is useful for those geotechnical problems in which climatic actions are impactful, as in the case of slope stability assessment. Yet, conventional engineering approaches ignore its impact on geotechnical design and assessment, due to the intri...

This paper presents a reliability analysis referred to backward erosion piping phenomena. The study is carried out on a cross-section of the major Italian watercourse, the Po River, where evidence of piping effects, namely a sand boil of remarkable size, has been periodically detected during past high-water events. The initiation of the process has...

This paper concerns the numerical analysis aimed at reproducing the centrifuge test conducted on a clayey silty sand river embankment, compacted in unsaturated conditions and subjected to a simulated flood event. To investigate the observed behavior during different stages of the test, characterized by incremental acceleration fields, a finite elem...

This paper reports the results of a centrifuge test on a silty sand river embankment compacted in unsaturated conditions and subjected to flooding. The measures of pore water pressure from tensiometers and pore pressure transducers show that the saturation line reaches the landside only after an unrealistic long-lasting flood, proving that the assu...

In the present contribution, a seepage induced in an earth river embankment is investigated by numerical simulations, using soil characterization derived from an experimental laboratory investigation and varying the boundary conditions to the embankment according to a centrifuge test. A validation of the scaling laws of the processes involving wate...

In questo lavoro sono riportati i risultati sperimentali di una prova in centrifuga su un modello di argine fluviale soggetto ad una progressiva sollecitazione idraulica. Le misure di pressioni neutre e di suzione nell'argine mostrano che il fronte di saturazione raggiunge il lato campagna attingendo la condizione stazionaria solo dopo una persiste...

Sommario Il contributo descrive una strategia per la modellazione numerica bidimensionale del moto di filtrazione in regime transitorio che si sviluppa in una sezione arginale del fiume Po, al variare del livello idrometrico del fiume. La sezione di indagine, che si trova in località Guarda Ferrarese (FE), è sede di un ''fontanazzo'' (sand boil) st...

La nota illustra sinteticamente le fasi di esecuzione e le modalità interpretative di prove triassiali consolidate drenate (TXCD) condotte su una miscela di sabbia e limo argilloso, costipata in condizioni di parziale saturazione. Le prove a controllo di suzione sono state eseguite utilizzando una cella triassiale a doppia parete, il cui piedistall...

When dealing with unsaturated soil conditions, the influence of matric suction on cone tip resistance of the soil above the ground water table is typically neglected in engineering practice, with consequent possible misinterpretation of soil features. In the last decades, various researchers have investigated the influence of suction on cone resist...

Backward erosion piping is one of the most critical issues for the stability of many river embankments worldwide. The article presents results from an extensive geotechnical campaign carried out on a section of the Po river embankments (Italy), prone to backward erosion piping. The aim of the investigations was twofold: firstly, identifying the str...

Post-depositional phenomena can produce significant changes in the geotechnical properties of soils. Although the identification of the effect of such phenomena on the soil structure may contribute significantly to the interpretation of the soil mechanical behaviour, their characterization is not routinely carried out in practice. In this context,...

Garisenda and Asinelli, also known as the Two Towers, are the best preserved medieval towers in the city of Bologna (northern Italy). They are worldwide famous symbols of the past power and wealth of the city which in the 12th century counted more than 75 masonry towers and tower-houses. In order to preserve these invaluable monuments, a deep under...

The Garisenda Tower and the Asinelli Tower, also widely known as the Two Towers, are the best preserved and famous medieval towers in the city of Bologna (Northern Italy). Standing one close to the other, right in the heart of the city centre, the Two Towers are delicate remains of the old towered city, which counted more than 75 towers in the 12th...

Following the 2012 Emilia-Romagna seismic sequence, widespread liquefaction of silty sands was observed, providing the opportunity to enhance our knowledge of the influence of fines content on seismic hazard and mitigation works. This paper presents the results of a thorough geotechnical investigation performed in connection with full-scale control...

Il frequente manifestarsi di eventi alluvionali per collasso di opere in terra costituisce un problema di particolare rilevanza nella valutazione del rischio idrogeologico e della pianificazione territoriale. In questo contesto risulta cruciale un’accurata stima delle condizioni di stabilità che tenga conto dello stato di parziale saturazione dei t...

La valutazione delle condizioni di stabilità delle opere in terra rappresenta una difficoltà spesso sottovalutata nella pratica ingegneristica e, viceversa, di attualità della ricerca scientifica in geotecnica. Infatti, è certamente vero che il contenuto d’acqua dei terreni costituenti tali opere e la distribuzione della pressione interstiziale nel...

Il contributo è centrato sulla modellazione della filtrazione in regime transitorio all’interno di una sezione arginale strumentata del fiume Secchia, presso Cavezzo (Modena) nel periodo temporale 2017-2018. Il codice commerciale Hydrus 2D di Pc-Progress è stato utilizzato per condurre tali simulazioni dirette. Differenti modelli idraulici sono sta...

Sand boils are the surface manifestation of an erosion process, known as backward erosion piping, which may take place beneath river embankments during high-water events. The risk of embankment failure greatly increases in locations affected by sand boils. Numerous studies have been carried out, mainly at the laboratory scale, providing significant...

The article presents a three-dimensional (3D) finite element (FE) model of the groundwater flow beneath a river embankment, aimed at developing a simple and reliable numerical strategy for the identification of hydraulic conditions that cause the reactivation of sand boils in flood defense systems prone to recurrent backward erosion piping. The see...

The paper presents a probabilistic study aimed at investigating the role of the soil hydraulic response on the stability of existing river embankments, for which the uncertainty and the inherent variability of geotechnical and hydraulic properties are typically greater when compared to new flood defence structures. The study has been carried out wi...

Paleosols are recurrent features in alluvial successions and provide information about past sedimentary dynamics and climate change. Through sedimentological analysis on six sediment cores, the mud‐dominated succession beneath the medieval ‘Two Towers’ of Bologna was investigated down to 100 m depth. A succession of weakly developed paleosols (Ince...

River embankments stability is a key aspect in geohazard assessment and underestimating its failure risk may result in unexpected and severe damages. Changes in hydraulic and climatic boundary conditions are responsible for transient water flow within the embankments, consequently the related soil water content and pore-water pressure distributions...

Time-dependent boundary conditions, uncertainties and variability of soil suction and water content of the filling material together with the use of proper retention and strength soil models are crucial aspects to be included for reliable analyses of the actual stability of river embankments. However, due to a typical lack of information in many pr...

Backward erosion piping is one of the most critical issues for the stability of the Po River embankments, which are reported to have experienced more than one hundred episodes of sand boils over the last century. This phenomenon is particularly widespread in the Po River for structural, hydrogeological and climatic reasons. This paper describes an...

Soil mechanical behaviour is strictly related to its natural water content, which is primarily dependent on hydraulic boundary conditions. When soils are partially saturated, as frequently occur in river embankments, soil suction also turns into a fundamental variable worth of investigation and monitoring, both in laboratory and in the field, for a...

The paper presents the results of an experimental campaign aimed at characterizing the hydro-mechanical behaviour of a sandy silt from a river embankment. Due to continuous river level fluctuations and changing climatic and environmental conditions, flood embankment materials experience frequent variations in degree of saturation and suction values...

In the engineering geology field increased attention has been posed in recent years to potential liquefaction mitigation interventions in susceptible sand formations. In silty sands this is a major challenge because, as the fines content increases, vibratory methods for densification become progressively less effective. An alternative mitigation te...

This paper outlines the multidisciplinary approach developed for the definition of the geotechnical model of the foundations of Asinelli and Garisenda towers in Bologna. Historical information and previous site investigations were collected and analysed. Then a new geotechnical investigation was carried out in 2016, which enabled accurate identific...

This study presents the application of the Boolean Stochastic Generation (BoSG) approach to the case study of the Mortisa landslide, an active earth slide flow in the Dolomites (Italy). The approach relies on the stochastic generation of different soil profiles for which the interfingering of distinct layers within a prevailing matrix is randomized...

Skirted foundations are an attractive foundation concept in the offshore energy sector, both for wind turbines and oil and gas platforms. Most of the evidence of skirted foundation behaviour under combined vertical, horizontal and moment (VHM) loading in sand has been collected from small-scale model experiments conducted at unit gravity on the lab...

Steel wire meshes are a key component of rockfall protection barriers. The efficiency in reproducing the structure response with numerical methods relies upon the specific modelling technique employed to capture the wire mesh behaviour. The fabric of some rockfall meshes, such as chain-links is quite complex, which leads to sophisticated and costly...

The paper presents a new approach to assess the effecctiveness of rockfall protection barriers, accounting for the wide variety of impact conditions observed on natural sites. This approach makes use of meta-models, considering a widely used rockfall barrier type and was developed from on FE simulation results. Six input parameters relevant to the...

In situ measurements of soil suction and water content in deep soil layers still represent an experimental challenge. Mostly developed within agriculture-related disciplines, field techniques for the identification of soil retention behaviour have been so far employed in the geotechnical context to monitor shallow landslides and seasonal volume cha...

The crucial role of geotechnical engineering in the preservation of historic heritage is already well known and the need for accurate site investigations and long term monitoring data is essential for a proper study of valuable historical monuments. In such a framework, this paper describes the case study of the two leaning towers of Bologna (Italy...

The reliability of river embankments is essential for flood risk management. The Po River, which flows through the North of Italy, is safeguarded over half of its length by major river embankments. Performance assessment of such water-retaining structures has become a major concern following some significant flood events in the past. Among the poss...

Le variazioni a carattere stagionale del contenuto d'acqua nei terreni coesivi determinano lo sviluppo di fenomeni di ritiro e rigonfiamento, a cui si associano deformazioni volumetriche e, conseguentemente, cedimenti e sollevamenti del piano campagna, che possono ripercuotersi sulle strutture in elevazione ed essere causa di danneggiamenti e fessu...

In order to investigate the effective role of sedimentological analysis in the interpretation of geotechnical data, with special reference to coastal transitional paleoenvironments, a study on the Quaternary alluvial and coastal plain successions forming the upper 30 m of the Tronto River valley subsoil, facing the Italian Central Adriatic Sea, has...

The paper addresses the response of a semi-rigid rockfall protection barrier using numerical models. The study show a large dependence of the barrier response to the impact conditions. The block size and impact position, rather than the velocity direction and magnitude induce different modes of failure of the fence, which in turn result in differen...

The research presented in the paper moves from the results of a feasibility study recently carried out for the development of an offshore wind farm off the cost of Rimini, in the Northern Adriatic Sea. The work, based on in-situ measurements of the environmental conditions, assessed the suitability of the considered area for the development of a re...

The Po River (Northern Italy) is the longest watercourse in Italy and over half of its length is safeguarded by major river embankments. Their stability is crucial for the local communities, being the Po River plain densely populated. Among all possible failure mechanisms, backward erosion piping at the interface between the bottom sandy aquifer an...

The evaluation of riverbank stability is a fundamental problem in flood risk management, representing a critical task for engineering practice. Soil heterogeneity together with initial and boundary conditions are among the crucial issues that should be considered to obtain an accurate solution of the problem. Generally, attention and efforts are mo...