Presentazioni ad invito
Prof. Gioacchino Viggiani
Université Grenoble Alpes, Laboratoire 3SR, Grenoble, France
Recent developments in laboratory testing of geomaterials, with emphasis on imaging.
This talk will present a review of some recent technical developments and scientific accomplishments in laboratory experimental testing of geomaterials – with a special focus on imaging. In particular, I'll provide a few examples of studies using full-field techniques such as x-ray and neutron tomography. These two techniques have had a strong impact over the last two decades, and have allowed the understanding of the micro scale processes ultimately driving the behavior of geomaterials at the macroscopic scale. I will try to outline the broader impact that this panoply of techniques has had and is expected to have in geomechanics and geotechnics at large.
Prof.ssa Daniela Boldini
Dipartimento di Ingegneria Chimica Materiali Ambiente, Sapienza Università di Roma
The response of framed structures to tunnelling: experimental results, numerical assessment and monitoring evidence.
The expansion of the urban infrastructural system requires the development of risk assessment approaches for properly analysing complex soil-structure interaction problems deriving from the construction of underground constructions. Nowadays the ever-increasing computational potential offers the possibility of performing coupled three-dimensional numerical analyses, capable of accounting into a single model the construction phases, for example, of tunnels, the surrounding soil and the structures influenced by the excavation. However, it is essential that these models undergo a rigorous validation process, possible in the specific case thanks to the availability of closed-form solutions for free-field conditions, but also of advanced centrifuge experimentation techniques and monitoring measures to compare the ex -post observed behaviour with predictions.
The paper summarises a series of researches aimed at investigating the response of framed structures to tunnelling in coarse-grained soils. The activities were developed with a twofold objectives: on the one hand, an extensive experimental campaign of centrifuge tests was designed and carried out in order to obtain a consistent set of data, although for simple geometric configurations of the structure and of the tunnel-to-structure relative position; on the other, attention was paid to the fundamental ingredients to be included in the numerical models, essentially in terms of tunnel excavation simulation procedures, adopted detail in the schematisation of the structural components and constitutive laws to describe the non-linear soil and structural response, as well as their interaction. Validation of numerical models on the basis of the experimental results allowed them to be used to extend the analysis to further configurations and to fully define the so-called modification factors of the maximum angular distortion of the span, identified as the main indicator of the damage to due to the high shear flexibility of this type of constructions, as a function of the relative soil-structure shear stiffness. These charts can be used in the engineering practice for a first estimate of the possible damage associated to tunnelling.
In addition to the direct comparison with the centrifuge data, the developed numerical strategy was also validated with respect to the in situ observations carried out over a stretch of the Milan metro line 5. This case study was also used to perform a numerical exercise, through inverse analysis and meta-modelling procedures, to optimize the position of the monitoring sensors, compared to the real one, for a possible real-time calibration of the soil constitutive and the TBM-EPB machine parameters used in the numerical modelling.
The methodology adopted highlights how the multi-disciplinary approach to research activity and the complementarity of specific skills in the sectors of laboratory testing, computational mechanics and monitoring of full-scale constructions are essential ingredients for understanding complex phenomena of soil-structure interaction.
Prof.ssa Anna D’Onofrio
Dipartimento di Ingegneria Civile Edile e Ambientale, Università di Napoli Federico II
A multi-hazard perspective in the evaluation of seismic induced ground instability: the case of Ischia Island.
Italy is one of the nations most exposed to natural risks. As a matter of fact, the whole territory is characterised by an intrinsic fragility deriving from its peculiar morphologic, geologic, seismic, hydrogeologic features. Such a fragility is enhanced by the actions deriving from the unrelentless climate change that influences both intensity and frequency of meteoric hazards, and from the anthropogenic pressure related to the rapid and unregulated growing of urban environment.
The combination of these predisposing actions results in an extremely high susceptibility of the whole territory to triggering events, such as intense and prolonged rainfalls, land and coastal storms, unusual drought periods, strong-motion earthquakes, volcanic phenomena, and other natural hazards frequently occurring in whole Italian peninsula. The enhanced vulnerability of the urban environment due to its progressive aging as well as the lack of maintenance and the growth of its exposure related to the raising intensity and interconnection of human activities lead to an increased complexity of the resulting risks.
As a matter of fact, last disaster events, related or not to COVID 19, demonstrated that it is no more possible to apply mitigation strategies considering one risk at a time, but it is compulsory to analyse risk considering its complex nature deriving from the strong interaction among the different predisposing and triggering factors. This is true at any considered scale and with reference to any disaster cause.
A current key issue towards mitigation of natural risks is the transition from the conventional single hazard evaluation to multi-hazard approaches, in order to account for the possible combination of predisposing factors, preparatory phenomena and triggering events inducing cascading effects. In this study, a multi-hazard approach is tentatively adopted with reference to the evaluation of ground instability and permanent deformation related to liquefaction and landslides in the volcanic island of Ischia. This environment, well known for the richness of its hydro-thermal resources, was frequently interested by instability caused by hydro-meteoric and seismic events, the latest of which occurred with an unusual spatial and temporal concentration in 2009, 2017 and 2022 in the same area of Casamicciola. A multi-disciplinary multi-level approach has been carried out to accurately define the predisposing and preparatory factors, as well as the critical events triggering ground instability in the studied area. A careful collection of geological, geophysical and geotechnical data has been carried out aimed at defining geometric and mechanical properties of the volcanic granular deposits covering the island, which are characterised by a high degree of heterogeneity and, insofar, have been poorly investigated under the geotechnical viewpoint.
A specific study has been conducted in cooperation with researchers operating in the fields of geology and seismology aimed at better characterising the peculiar seismicity of the island related to its volcanic nature. Synthetic reference input motions were defined, based on specific simulations of the source slip and deep propagation mechanisms. Different quantitative scenarios of ground instability caused by the seismic triggering events have been produced by adopting a multi-level approach for both slope displacement and liquefaction. From the perspective of multi-hazard analysis (Zschau, 2017), potential cascading effects related to ground instabilities were investigated considering both the ‘multi-layer single hazard’ (i.e. no interaction between hydro-geological and seismic hazard) and the ‘multi-hazard’ approaches (i.e. hazard interactions considered). In the first approach, the hydro-meteoric action has been considered as a predisposing factor preceding a strong-motion earthquake, i.e. the variable susceptibility to seismic instability was related to the seasonal groundwater fluctuation and to a maximum potential earthquake. In the second case, the annual rate of occurrence of a strong-motion earthquake was probabilistically combined with the chance of having a concurrent extreme meteoric event.
The procedure adopted may represent a methodological proposal for the definition of realistic scenarios induced by cascading hazards, and to provide an estimate of their impact on the built environment through the determination of suitable engineering demand parameters related to co-seismic soil deformation. This in turn may contribute to the objective of vulnerability reduction and risk mitigation through adequate engineering and urban planning solutions.
Prof. Alessio Ferrari
Dipartimento di Ingegneria, Università di Palermo
Thermo-Hydro-Chemo-Mechanical Couplings in Energy Geotechnics.
Geomechanics and geotechnical engineering are at the core of the energy scientific and technological challenges of this century. Most of new and conventional technologies for energy production, transportation, storage and disposal of related waste require in fact a deep understanding of the mechanical behaviour of geomaterials, which are often subjected to complex sequences of multiphysical coupled processes, involving non-isothermal conditions, cycles of wetting and drying, and perturbations of the original pore fluid composition. The understanding and the prediction capability of the thermo-hydro-chemo-mechanical response of the involved geomaterials are therefore fundamental requirements in order to design, analyse and assess the long-term behaviour of energy-related geotechnical systems. The presentation will summarize recent advances on the experimental tools and constitutive modelling of these coupled multiphyiscal phenomena. Best practises to introduce these couplings in the study of the geotechnical systems will be discussed, along with the presentation of the their application to real case studies.
Prof.ssa Maria Rita Migliazza
Dipartimento di Ingegneria Strutturale, Edile e Geotecnica, Politecnico di Torino
Rock mass characterization with advanced measurement systems for Reliability- based design.
The design of works involving rock masses must take into account the rock mass discontinuous nature that strongly influences their mechanical behaviour in terms of their response to any stress-strain perturbation. Stress strain behaviour of rock masses is linked to both, the mechanical characteristics of rock matrix and to the rock mass degree of fracturing.
The characterization of rock masses requires approaches at different scales (microscale, laboratory, site and, sometimes, regional scale) each of which provides different information that can be very relevant from a design point of view. At the microscale, information regarding petrographic and mineralogical features can be acquired and analysed in relation to the mechanical behaviour of rock matrix and discontinuity studied with laboratory tests . At the site scale information related to discontinuity geometry such as orientation, persistence and spacing can be acquired by different measuring methods.
All measured quantities show a natural randomness due to both epistemic and aleatory uncertainties. In order to reduce the epistemic uncertainties a representative and sound number of measurements must be taken, whilst probabilistic analyses need to be performed to analyse the aleatory nature of each variables. The representativeness of the data and a correct statistic analyse allow for sound reliability analysis.
The aim of this contribution is to present innovative and multidisciplinary approaches applicable at different scales for the identification and measurement of all the quantities necessary for a sound characterization of rock masses in order to apply appropriate rock mass modelling and reliable design approaches in line with the reference standards for the geotechnical design.
Prof. Marco Uzielli
Dipartimento di Ingegneria Civile e Ambientale, Università di Firenze
The trends, triumphs, and tribulations of data in non-deterministic geotechnical design.
Geotechnical systems are pervaded by relevant uncertainties stemming from the real complexity of the natural environment as well as from limitations in geotechnical and modelling capabilities. Over the past decades, non-deterministic approaches, in which uncertainties are modelled, processed, and reported explicitly, have earned an increasingly relevant centrality in geotechnical analyses aimed at characterization and design. Far from being limited to an academic context, non-deterministic geotechnical analyses have widely proved to be instrumental to cost-performance optimization. Consequently, numerous geotechnical design codes have evolved from traditional deterministic formats to non-deterministic formats and continue to evolve within the non-deterministic domain. While inspired by the virtuous growing global awareness towards the ethical management of resources and driven conceptually by innovative approaches and ingenious mathematical techniques, this momentous shift in geotechnical design paradigm is made possible and fostered in practical terms by technological advances related to ever-increasing computational power and data collection. Rigorous, reliable, and meaningful non-deterministic design requires “adequate” amounts of “adequately” high-quality data. Through a structured insight into the components of geotechnical uncertainty, the conceptual foundations and operational formulation of non-deterministic design approaches, and salient aspects of best-practice modelling of uncertainty for non-deterministic design, this paper illustrates and highlights the central role of data in pursuing cost-performance optimization. The paper also presents and discusses critically the largely cultural obstacles which prevent the full exploitation of design potential and the consistent attainment of the subtle threshold of “adequateness” in current geotechnical practice.