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Computational investigation of the stability of natural slopes within a coupled hydro-mechanical approach becomes more and more attractive due to an increasing number of slope movements caused by heavy rainfall events. Seasonal cycles of summer drying and winter-spring wetting affect the stability and serviceability of natural and man-made slopes, threatening lives and property worldwide. Heavy rainfall will increase the soil moisture content and lead to a reduction in suction and a consequent weakening of the soil. As a result, the slope may fail either in a diffused or in a localized pattern. The localization process is a classical mode of mechanical instability and is described as the concentration of shear strains in narrow bands within the soil strata. As it is well-known, the width of those bands cannot be properly computed using the standard continuum mechanical approach with unstable materials (in the sense of Drucker). In the framework of the standard finite element method the computation of shear band phenomena reveals a strong mesh dependency of the numerical solution and the objectivity of the computational results is blown. Each mesh refinement results in an overall different outcome and the width of the localization band has the size of the element of the adopted mesh. In the literature two main categories of methodologies can be found for regularizing this problem. One is to simulate the formation and propagation of such discontinuities via suitable enrichment functions and is the concept of the so-called extended finite elements. The other solution is to exploit enhanced continuum theories. These theories contain an internal length scale which is an additional material parameter related to the shear band width and removes the spurious mesh sensitivity of the numerical simulation results. The present work is focused on the second category. In this context, viscoplasticity and non-local theories are adopted to effectively study strain localization mechanism, assuming the soil as a multiphase porous medium. This means that the localization analysis is considered as a fully coupled hydro-mechanical problem with the material consisting of an elasto-viscoplastic skeleton and open pores filled with incompressible liquid water and compressible gas. Both regularization techniques are physically sound. Rate dependency is experimentally motivated as the mechanical response of granular materials seems to be rapid, but not instantaneous and a viscoplastic constitutive model is able to reproduce creep and relaxation processes. The physical interpretation of the non-local theory stems from the fact that no real material is an ideal continuous medium and the evolution of the microstructure at one point influences the surrounding points when irreversible strains take place. Two types of viscoplastic models are applied; the Perzyna and the Duvaut-Lions. The former is extended with respect to the non-local integral approach. In the first part of this work, the generalized effective stress is limited by the Drucker-Prager yield criterion. The models are implemented and numerically validated in the finite element code Comes-geo and further verified by simulating an experimental plane-strain biaxial test and a benchmark slope failure problem. This work is in essence aimed at answering key questions, such as: what are the most significant influential factors in the development of strain localization for each regularization technique and what is the role of suction and drainage conditions; is the viscosity of the soil affected by the presence of water and how does this fact influence the regularizing capabilities of the method; how do the internal lengths introduced by viscosity and non-locality interact with each other and under which circumstances is the one method preferable to the other? The second half of this work comprises the extension to viscoplasticity of the existing advanced elastoplastic constitutive model for unsaturated sands developed by Buscarnera and Nova. This model allows for hydraulic bonding and debonding effects and therefore the main mechanisms of unsaturated materials are captured. The elastoplastic version of the model is first implemented in the finite element code Comes-geo and validated with results from the literature. The model is then extended to viscoplasticity and is also implemented and validated in the code. The proposed viscoplastic formulation, as further novelty, is enhanced with the dependence of the constitutive parameters on the relative density. To validate the elastoplastic model in the finite element code Comes-geo a series of tests are simulated: triaxial shear tests at different suction and net confining pressure, oedometric tests with drying and wetting paths and triaxial and plane-strain compression tests in drained and undrained conditions. The viscoplastic model is also validated through oedometric tests, creep tests and triaxial compression tests on different sand densities. The onset of shear strain localization is then studied and the finite element results are compared with the results of a theoretical stability analysis. The verification of the viscoplastic model is finalized with the simulation of a triaxial compression test. The main motivation for the present work stems from these premises and this thesis presents an efficient tool to simulate strain localization with regularization techniques, which do not need to increase the number of the state variables of the numerical model, taking into account fully coupled hydro-mechanical analysis and using advanced constitutive model for unsaturated sands. This dissertation has been performed for the first two years in the University of Padova (Italy) and for the last year at Baugrund Dresden (Germany), geotechnical design and construction company within the Marie Curie Initial Training Network project MuMoLaDe (Multiscale Modelling of Landslide and Debris flow, 7th Framework Programme of the European Union, project n. 289911, http://www.mumolade.com/). This practice is in the scope of linking academia and industry and the transfer of knowledge. In this framework, the advanced elastoplastic and elasto-viscoplastic models for unsaturated soils are implemented and validated in PLAXIS commercial finite element analysis software. The validation included single element tests of drained and undrained triaxial loading and triaxial tests at different suction levels. The implementation is verified and the effectiveness of the model is displayed by numerical simulations of a partially saturated slope failure of the laboratory scale.

Shales are among the most commonly considered geomaterials in current energy-related geomechanical investigations, as they are involved in engineering applications such as the unconventional extraction of natural gas, CO2 sequestration and nuclear waste geological storage. A deep understanding of their hydro-mechanical behaviour is of primary significance for such applications. In this paper selected results on the water retention behaviour and on the high pressure oedometric compression behaviour of shales are presented.

Precipitation, together with erosion and earthquakes, have been recognized as the main triggering factors of shallow landslides. However, there are relatively few well-documented cases where direct relationships could be established between occurrence and features of shallow landslides, the rainfall characteristics (e.g. intensity, duration) and water retention curves. A field experiment has been performed on a steep forested slope located on the east-facing banks of the river Rhine in Ruedlingen, northern Switzerland. The aim of the experiments was to study the triggering mechanisms of the landslides induced by rainfall. The pore pressure and the degree of saturation, which are linked through the water retention curve, represent two of the main variables affecting the mechanical behaviour of unsaturated soils, and their relationships to rainfall are complex. The difference in the determination of water retention curves at different scales are analysed in this paper for Ruedlingen soil together with their effects on mechanical behaviour at multi-scale., E3S Web of Conferences, 9, ISSN:2267-1242

The geo-energy sector makes use of advanced technologies such as shale gas extraction, CO2 sequestration and nuclear waste geological disposal that rely on the exploitation of shale formations. Due to the great depths involved in these applications and the difficulties in retrieving intact samples, remoulded shale specimens are often adopted for hydro-mechanical testing. Remoulded and intact shales may substantially differ in their hydro-mechanical behaviour due to the particular structure of the natural material, which is the result of diagenesis and burial history. This paper presents an experimental campaign aimed at (i) characterizing the role of diagenesis and depth for Opalinus Clay shale and their impact on the hydro-mechanical behaviour of the material and (ii) understanding how representative the behaviour of the remoulded material is with respect to that of the natural shale. In this paper, the hydro-mechanical behaviour of remoulded and intact specimens from the Opalinus Clay shale formation is investigated by means of a comprehensive oedometric testing campaign. The effects of depth and diagenesis on the material behaviour are analysed by testing intact specimens that come from two different sites and depths of the considered shale formation. The results highlight a considerably greater stiffness for the natural Opalinus Clay with respect to the remoulded specimens when the same vertical effective stress is considered, together with a significantly lower porosity for the former, which is shown to be the result of diagenetic processes rather than solely mechanical compaction. A lower swelling sensitivity is also manifested by the natural material with respect to the remoulded specimens as a result of the formation of bonding; on the other hand, the diagenetic processes do not seem to have a strong impact on the permeability of the material. Finally, creep effects are reduced when diagenesis occurs, while they become more relevant when the material is disturbed or remoulded. The obtained results provide significant insight into the roles of depth, diagenesis and structural disturbance on the hydro-mechanical behaviour of the Opalinus Clay shale.

La nota presenta i risultati di un programma sperimentale mirato alla valutazione della possibilità di utilizzare le argille a scaglie trattate con calce come materiale di sottofondo per opere di Ingegneria Civile. Tali risultati evidenziano che le caratteristiche di tale materiale migliorano rapidamente nel tempo e che esso diventa, dopo 28 giorni dal trattamento, molto stabile nei riguardi delle sollecitazioni dinamiche indotte dal traffico veicolare, simulate in laboratorio attraverso l’esecuzione di prove di compressione triassiale cicliche mirate alla misura del modulo resiliente.

This paper aims to investigate the hydro-mechanical behaviour of a loosely compacted embankment during an inundation event. This study is based on the results of a centrifuge test carried out on a small-scale embankment model made of an artificially compacted clay-sand mixture. The wetting-induced displacements are analyzed and interpreted by means of a constitutive model adapted to unsaturated conditions. The numerical predictions are presented in terms of time evolutions of settlements, as well as, spatial distributions of vertical displacements. These profiles are compared to those experimentally observed in order to validate the predictive capabilities of the model on a boundary value problem. Moreover, the stress paths followed by elementary soil elements located at different depths are analyzed to emphasize the stress and strain variations due to capillary rise.

Internal erosion is the cause of a significant percentage of damages involving water-retaining structures all over the world. In most cases, however, early detection of the phenomenon allows avoiding dramatic accidents. Developing monitoring techniques capable of detecting ongoing internal erosion with sufficient advance represents therefore a significant step towards a higher level of flood safety. Temperature measurements performed in embankment dams have been proven to be effective in identifying leakages consequent to internal erosion. This work investigates the effectiveness of distributed fibre-optic temperature sensing for the early detection of internal erosion in river and sea dikes. The attention is focused on dikes prone to backward erosion piping, a mechanism that affects the foundation layer of structures resting on sandy soils. The measurements performed in a large-scale piping test are presented and discussed. The test enabled the recognition of the main factors that influence the onset of thermal anomalies in regions affected by piping. Subsequently, the effect of the above-mentioned factors was quantitatively studied with the aid of finite element modelling and dimensional analysis. It was discovered that early detection of piping cannot completely rely on the propagation of a thermal front (hot or cold depending on the season) that moves from the waterside to the landside with different speed in intact and eroded regions. Indeed, depending on the permeability and thickness of the sandy layer and on the size of the embankment, the duration of the flood event might not be sufficient for the front to reach a pipe not yet fully developed. However, another mechanism is exploitable for detection: the effect of the flow velocity on the natural vertical temperature gradient. Since this gradient decreases with depth, the effectiveness of this mechanism depends on the depth at which piping occurs. The thesis also contains some tips for an effective numerical modelling of the advection-diffusion equation in permeable soils, both intact and affected by piping. Finally, the thesis describes a small-scale setup that was developed to investigate the temperature distribution in the surroundings of a pipe. The model incorporates a distributed fibre-optic sensor with a sub-centimetre spatial resolution. Such resolution was achieved adopting a novel sensing technology, in which the spectral shift of the Rayleigh backscatter is measured using optical frequency-domain reflectometry. Preliminary results show how the cross-sensitivity of the sensor to temperature and strain influenced the measurements and how this was partially overcome.

The protection of soils against compaction requires knowledge of the mechanical behavior and properties of structured unsaturated soils and their dependence on soil moisture. This study of an agricultural silt loam soil is based on undisturbed specimens from the plow layer (7-17 cm depth) and two subsoil layers (47-57 cm and 67-77 cm depth) conditioned to five initial suctions (s = 1, 3, 6, 16, 32 kPa) per layer and compressed under drained, confined uniaxial stress. From the resultant total axial stress versus void ratio curves, effective axial stress versus void ratio curves were calculated using a modified form of van Genuchten’s equation (van Genuchten, 1980). The effective axial stress versus void ratio curves were fitted using the unsaturated soil mechanics model by Casini (2012). The effective initial precompression stress, compression, and recompression indices and the soil mechanical parameters N and b were then determined for the plow and subsoil layers. Based on Casini (2012), a model was developed to predict the effective initial precompression stress from the initial void ratio and suction or saturation degree. The Casini (2012) model was successfully fitted to the effective axial stress versus void ratio curves recorded in the confined uniaxial compression tests on the specimens, as well as the relationship of the effective initial precompression stress to the initial void ratio plus the initial degree of saturation and suction. The results show that some measure of soil density (void ratio) is equally as important as soil moisture to describe compression behavior for structured, undisturbed soil.

International audience

Italy is a country susceptible to various and numerous natural disasters; landslide hazard is certainly one of the most important topics here, so the research for innovative and cost-effective solutions for landslide stabilization has great scientific and socio-economic relevance. This PhD fits the context by studying and developing a new technique for the stabilization of landslides, called “floating anchor”, both in theoretical and applied aspects. The technique involves the installation of passive nails in the landslide body, cemented along the entire profile with a sufficient foundation in the deep stable soil. The anchors fit the slope according to a discontinuous geometry without a continuous facing. Each anchor head connects only to a small concrete plate (the “floating” element), which may be bored in the soil. The reinforcements absorb by frictional contact a portion of the shear stress induced by the moving landslide, slowing down its evolution process until it completely stops. It is a modular and flexible technique; the system fits the soil deformations without losing effectiveness. The PhD work analyses all the components of the system in order to assess the geotechnical and structural behaviour. A comparison with the techniques commonly used for landslide stabilization highlights the main advantages of the floating anchors, both in efficiency and cost terms. An important part of the research focuses on the experimental analysis in a 1g scale physical model of the behaviour of floating plates as a function of their shape. An equation for the calculation of the bearing capacity of the floating plate with the introduction of specific shape and volume factors has been determined. A FEM analysis provides a numerical model calibration based on the experimental results and highlights the influence of the plate on the soil stress-strain state. Specific guidelines for the design of floating anchors are proposed according to two physical-mathematical configurations: one “static” short-term approach and one long-term approach, assuming a non-linear viscous behaviour of the soil. At last, some applications complete the research: the development of a particular enhanced anchor bar (the “composite anchor”), and the design and execution of some stabilization works with floating anchors in four real landslides activated in North-Eastern Italy in conjunction with the exceptional rainfall that affected the area in autumn 2010. The monitoring of the stabilized slopes proves the viability and technical efficiency of the method.

The numerical simulation of real geomechanical problems often entails an high level of complexity; indeed they are often characterized by large deformations, soil-structure interaction and solid-fluid interaction. Moreover, the constitutive behavior of soil is highly non-linear. Landslides, dam failure, pile installation, and undrground excavation are typical examples of large deformation problems in which the interaction between solid a fluid phase as well as the contact between bodies are essential. This thesis addresses the challenging issue of the numerical simulation of large deformation problems in geomechanics. The standard lagrangian finite element methods are not well suited to treat extremely large deformations because of severe difficulties related with mesh distortions. The need to overcome their drawbacks urged researchers to devote considerable effort to the development of more advanced computational techniques such as meshless methods and mesh based particle methods. In this study, the Material Point Method (MPM), which is a mesh based particle method, is exploited to simulate large deformation problems in geomechanics. The MPM simulates large displacements with Lagrangian material points (MP) moving through a fixed mesh. The MP discretize the continuum body and carry all the information such as mass, velocity, acceleration, material properties, stress and strains, as well as external loads. The mesh discretizes the domain where the body move through; it is used to solve the equations of motion, but it does not store any permanent information. In undrained and drained conditions the presence of water can be simulated in a simplified way using the one-phase formulation. However, in many cases the relative movement of the water respect to the soil skeleton must be taken into account, thus requiring the use of the two-phase formulation. The contact between bodies is simulated with an algorithm specifically developed for the MPM at the beginning of the century. This algorithm was originally formulated for the frictional contact. It extension to the adhesive contact is considered in this thesis, which is well suited to simulate soil-structure interaction in case of cohesive materials. In this thesis typical geomechanical problems such as the collapse of a submerged slope and the simulation of cone penetration testing are considered. Numerical results are successfully compared with experimental data thus confirming the capability of the MPM to simulate complex phenomena.

A case history concerned with the stabilisation of a slope-viaduct system is reported. The two-carriageway viaduct was built 39 years ago on a rather gentle slope that did not show any sign of instability. In 2010 a landslide took place and damaged the viaduct. As the relocation of the motorway was deemed unpracticable, the alternative solution of stabilising the slope and repairing the viaduct was chosen. The owner asked to design remedial measures that did not require the closure of the viaduct. This was possible since the movements of the slided mass were slow and regular. The slope-viaduct system was stabilised by improving, firstly, the bearing conditions of the decks, then strengthening the existing foundations of the involved piers, and finally stabilising the slope by reducing the pore water pressure by means of subhorizontal drains. The remedial works were successfully carried out and resulted to be effective.

L’articolo descrive uno studio riguardante i fenomeni deformativi osservati dopo il sisma dell’Emilia del maggio 2012 lungo un tratto di argine del Canale Diversivo di Burana che ricade nell’abitato di Scortichino, frazione del comune di Bondeno (FE). In questa porzione del rilevato arginale sono state edificate oltre un centinaio di abitazioni ed alcune strutture di medio-piccole dimensioni adibite ad attività produttive o a deposito, molte delle quali sono risultate pesantemente danneggiate e dichiarate inagibili proprio a causa delle deformazioni e del sistema di fratture longitudinali presenti nel terreno in seguito al terremoto. Il contributo qui presentato si prefigge di analizzare la risposta sismica dell’argine durante la sequenza sismica del 2012, comprendere le cause dei dissesti nonché individuare le necessarie azioni di mitigazione e gli eventuali interventi di messa in sicurezza nei confronti di terremoti futuri. A questo scopo è stata condotta un’ampia campagna sperimentale di indagini in sito e in laboratorio, finalizzata alla ricostruzione di un accurato modello geotecnico per la valutazione delle condizioni di stabilità dell’argine in condizioni sismiche, portando in conto anche l’eventuale insorgenza di fenomeni di liquefazione nei terreni sabbiosi superficiali costituenti la fondazione del corpo arginale. L’analisi illustrata è il risultato dell’attività di indagine svolta per più di un anno dal Gruppo di Lavoro Argini (GdLA), costituitosi nel luglio 2012 in seguito ad un accordo fra la Regione Emilia-Romagna e l’Associazione Geotecnica Italiana per la verifica delle condizioni di stabilità dei rilevati arginali nelle aree colpite dal terremoto.

Several empirical relationships allowing a preliminary estimate of debris flow runout distances have been proposed to correlate the runout length to the volume of the sliding granular mass, delimit potentially hazardous areas, and design safeguarding measures. To overcome their large variability and define their fields of applicability, an energy-based model, predicting debris flow mobility, is developed. The power balance of a granular mass sliding along two planar surfaces is written by taking into account the volume of the debris mass, the slopes of the sliding surfaces, an assigned interstitial pressure, the possible mass variation along the motion, the energy dissipation due to the grain inelastic collisions (“granular temperature” within a basal “shear layer”), and friction. A system of ordinary differential equations is obtained; its numerical solution allows, through parametrical analyses: (i) highlighting of the role of physical and mechanical parameters on the runout distance, such as grain size material, interstitial pressures, grain collisions, and erodibility of the crossed channel; and (ii) defining of the favourable conditions for debris flows mechanism generation. Finally, through the back-analysis of some cases, an original relationship to estimate the runout length, as well as to interpret the results of the empirical formulas, is proposed.

The Po River is the major Italian watercourse. Over half its length is controlled with embankments as protection measures against heavy floodings. Recently, the Italian Government has funded a project for the evaluation of the seismic stabil-ity of about 90 km of embankments of the Po River. The project mainly aims at the seismic stability analyses of the river banks, with assessment of local site response and evaluation of the liquefaction potential. Hundreds of geotechnical investigations within the study area were performed and the water level variations in the embankment and subsoil were investigated using piezometers. This paper describes the methodology and the main results of the analyses. The safety of 43 significant sections in static and seismic conditions was investigated using limit equilibrium analyses. Dynamic effects in the seismic condition were considered using the pseudostatic method. Local seismic hazard and effects of site conditions on the ground motion are taken into account in the definition of the expected seismic action. Eventually, the analysis results are summarized in a static and seismic stability map of the investigated area, a useful tool for the local Authority in the prevention and mitigation.

Hydraulic properties affect the shear strength of unsaturated soils in terms of suction, predicted as a function of water volume in the pores. In complex pore geometries, such as soils with bimodal pore-size distributions, suction effects on shear behavior are poorly understood. We present an analytical approach to define how a bimodal suction stress originates in such soils, which are conceptually divided into micro and macrostructures due to aggregation of a wide range of particle sizes. The results were compared with data from the literature for other soils with aggregated macrostructure or with a prevailing coarse fraction. A physically based dependence of soil shear behavior on the bimodal hydraulic behavior was observable, with the extension of the suction stress theory to a bimodal soil hydraulic response in agreement with the suction and moisture change. Depending on the soil type and the range of suctions investigated, the micro and macrostructures should prevail affecting the mechanical soil response subject to environmental loading, such as rainfall events. From a practical point of view, taking into account the bimodal structure network should be fundamental in the set-up of proper prediction models for shallow landslides induced by rainfall.

In this paper we study an imbibition test problem defined over a real two-dimensional soil domain subject to in-situ stresses and oedometric boundary conditions. Two different kinds of materials are tested, which are characterized by different pore-structures and hydro-mechanical properties. The aim is that of clarifying the behavior of real materials under real loading conditionss. The stress paths associated to rainfall infiltration processes are simulated by using the commercial code ABAQUS, endowed with an own-made sub-routine developed in order to incorporate the effects of partial saturation into the tangent stiffness.

The Latomiae (origin: Greek latomia, from laas, las stone plus –tomia tomy ) del Paradiso in Syracuse are Magna Graecia rock quarries, located in the coastal areas of Southern Italy and internationally renowned for their impressive environment. The few historical technical records do not help clarify the events that led to their current configuration since a series of instability phenomena occurred due to decay processes over time. Through a geotechnical back-analysis, this work highlights the failure phenomena, which may have led to the current configuration of the easterly side of the Latomiae del Paradiso. The back-analysis process was carried out by means of numerical modelling, supported by geological and meso-structural surveys, as well as a mechanical characterization of the rock mass and an extensive bibliographic and archival research. The result of this work highlights that geology and geotechnical engineering can help in retracing historical events that have affected cultural heritage, even if they are not mentioned in the official history. Such a reconstruction can be extremely useful for the prevention and risk assessment for the cultural heritage itself.

Nella nota si presentano i primi risultati di una indagine sperimentale volta a studiare l’effetto del trattamento con calce sulle caratteristiche microstrutturali di un’argilla di alta plasticità, proveniente dagli scavi eseguiti nel corso dei lavori di ammodernamento di una strada di grande comunicazione in Sicilia. I provini, compattati in laboratorio a diverse percentuali di calce, sono stati sottoposti a prove porosimetriche ad intrusione di mercurio MIP ed osservazioni al microscopio elettronico SEM. L’analisi dei risultati evidenzia che l’argilla trattata con calce assume una distribuzione dei pori tipica dei materiali a doppia porosità e che gli effetti sulla microstruttura dipendono dalla quantità di calce aggiunta e dal tempo di maturazione.

Si illustrano le misure degli spostamenti e delle pressioni neutre raccolte in un paio d’anni di osservazione del comportamento di un esteso corpo di frana in una formazione di argille varicolori in Sicilia. L’analisi delle misure raccolte indica che la riattivazione riguarda zone distinte del corpo di frana, nelle quali gli spostamenti si sviluppano con velocità e direzioni differenti. L’evoluzione degli spostamenti è manifestamente dipendente dalle condizioni climatiche, dal momento che essi aumentano al crescere delle pressioni interstiziali, a loro volta regolate dalle piogge, e rallentano nella stagione secca, spesso senza annullarsi del tutto. Analisi a ritroso effettuate in una delle zone maggiormente attive confermano che la resistenza a taglio mobilitata coincide con quella residua misurata in laboratorio. The paper reports some results of geotechnical investigations carried out to investigate the evolution of ground displacements in a large landslide measuring 1.6 km from top to toe (0.6 km at top, 1.2 km at toe) involving a varicoloured clay formation in the district of Palermo in Sicily. In order to analyse the landslide mechanisms and devise stabilization works, an extensive programme of in situ and laboratory geotechnical investigations was carried out, and a monitoring system was installed, comprising rain gauge, piezometers, inclinometers and numerous land marks to measure movements at ground surface. Monitoring was performed from instrument installation (autumn 2008/late spring 2009) until December 2011. The reactivation of the overall landslide was triggered by an earthquake in 2002 September, while successive monitored episodes are related to rising piezometric levels induced by rainfall. Several distinct active zones can be contoured where displacements are evolving at variable rates in different directions on the landslide surface. The evolution in time of the displacements is clearly affected by rain. With reference to two of the most active zones, labelled zones A and B, it is shown that displacement rates increase or decrease as piezometric levels rise or fall depending on rainfall. In zone A two active slip surfaces can be detected, located at different depths from ground surface, whereas back analyses carried out show that operative shear strength is consistent with the laboratory measured residual shear strength of the involved tectonised clays.

Il comportamento di un’argilla compattata sottoposta a cicli di imbibizione ed essiccamento viene analizzato attraverso l’esecuzione di prove edometriche a suzione controllata. I provini sono soggetti a diverse serie di variazione cicliche della suzione precedute da differenti percorsi di carico e scarico a suzione costante, allo scopo di studiare gli effetti del percorso delle sollecitazioni sulle deformazioni volumetriche e sulle variazioni di contenuto d’acqua indotte dalle variazioni cicliche della suzione. I risultati delle prove sono stati simulati con soddisfacente successo attraverso un modello costitutivo elastoplastico per terreni non saturi, in cui la risposta meccanica globale è dipendente dalle deformazioni della microstruttura, della macrostruttura e dalle loro reciproche interazioni.

This paper presents the methodology and the results of the local seismic analyses, performed in the bank areas of the Po River (Lombardia and Emilia-Romagna regions, northern Italy) characterized by the highest seismic hazard and finalized for the seismic stability analyses of the banks themselves. The proposed methodology includes the following steps: collection of the pre-existing information and geologic maps; deployment of in-situ investigations by collecting soil samples for geotechnical laboratory tests; definition of the geologic-geophysical and geotechnical model; individuation of the expected seismic inputs; analyses of local seismic response. In this paper, we mainly discuss the results obtained in order to illustrate how the methodology employed enables the definition of the local seismic hazard and allows performing the future stability analyses of the banks. The results are given in term of amplification factors, expected accelerograms and acceleration response spectra modified by the litho-stratigraphic characteristics of the sites. © 2014-OGS.

The archeological site of the Latomia del Paradiso (Syracuse) is endangered by severe instability phenomena due to the shape of walls and underground excava-tion related with the poor mechanical characteristics of the weathered and wet rock. The failure of huge blocks from the ceiling of the underground areas and the detaching of rock "flakes" from the walls surface make the geotechnical zon-ing particularly complex. the zoning is based on the characteristics of the rock wall surface that, in first approximation, can be distinguished in regularized sur-faces because of mining , and in irregular surfaces characterized by fracture prop-agation. The elaboration of reflectivity values obtained from a laser scanner survey pro-vides a quick and reliable method, which can be very useful to assess the localization of alteration processes and their intensity. Alteration processes affect the mechanical characteristics and a decay of a rock mass shear strenght is associated to them. Therefore, it has been possible to obtain a differentiated assessment of the safety conditions of the rock mass walls in areas where a direct assessment was too expensive or difficult because of the wall extension, or impossible. The measurements of reflectivity have been correlated to the Hammer Schmidt rebound values r both in soft rocks, such as those under consideration, and in stone formations of different rock types.

Engineering issues for which the understanding of the chemo-mechanical behaviour of soils is relevant include wellbore stability problems, the salinification of groundwater, and nuclear waste storage. However, despite the vast number of situations in which couplings between chemistry and mechanics occur, the available constitutive models rely on limited experimental evidence. This paper presents the results of an experimental programme on the chemo-mechanical behaviour of a non-swelling illite. The osmotic suction is controlled through the ion concentration of sodium chloride in the pore water. Stress paths include mechanical loading at a constant osmotic suction, and an increasing osmotic suction at a constant mechanical stress. The experimental results point out a correlation between the osmotic suction and initial oedometric modulus, as well as between the osmotic suction and yield stress. A constitutive framework for soils is extended to take the observed chemo-mechanical couplings into account. The numerical model has been calibrated for the illite using the parameters obtained through the tests under mechanical loading at a constant concentration, and validated using more elaborate stress paths. The presented experimental and constitutive investigation builds a basis for the assessment of engineering issues in which pore liquid chemistry plays a major role

Si riportano i risultati di una ricerca sperimentale sul coefficiente di spinta a riposo K0 di sabbie pomicee ottenute artificialmente per frantumazione dal materiale naturale. Lo studio è stato condotto fino ad alte pressioni efficaci verticali (100 MPa). Per questo studio è stato utilizzato un edometro speciale strumentato con estensimetri elettrici circonferenziali e verticali per la determinazione delle tensioni orizzontali e per la valutazione delle forze d’attrito all’interfaccia sabbia-parete interna dell’edometro. La sperimentazione è stata eseguita su sabbie “asciutte” ossia con contenuto d’acqua minore dell’1% (contenuto d’acqua in ambiente controllato). Il coefficiente K0 è variabile nell’intervallo 0,25 e 0,5 fino a valori della tensione verticale efficace v di 10 MPa circa. Per valori maggiori di v e fino ai valori massimi raggiunti K0 si mantiene all’incirca costante con valori dell’ordine di 0,35-0,5. Per le sabbie sovraconsolidate K0 è legato all’indice di sovraconsolidazione OCR mediante una relazione monomia del tipo di Schmidt. I valori di K0 misurati per queste particolari sabbie, aventi doppio ordine di pori, sono simili a quelli di altre sabbie (di quarzo e carbonatiche) molto differenti per natura e costituzione mineralogica.

Many abandoned room and pillar mines have been excavated not far from the surface of large areas of important European cities. In Rome, these excavations took place at shallow depths (3–15 m below the ground surface) in weak pyroclastic soft rocks. Many of these cavities have collapsed; others appear to be in a stable condition, although an appreciable percentage of their structural components (pillars, roofs, etc.) have shown increasing signs of distress from both the morphological and mechanical points of view. In this study, the stress–strain behaviour of soft rock pillars sustaining systems of cavities under vertical loads was numerically simulated, starting from the in situ initial conditions due to excavation of the cavities. The mechanical behaviour of the constituent material of the pillar was modelled according to the Modified Cam-Clay constitutive law (elasto-plastic with strain hardening). The influence of the pillar geometry (cross-section area, shape, and height) and mechanical parameters of the soft rock on the ultimate compressive strength of the pillar as a whole was parametrically investigated first. Based on the numerical results, an original relationship for pillar strength assessment was developed. Finally, the estimated pillar strengths according to the proposed formula and well-known formulations in the literature were compared.

Si presentano i risultati di una prova di campo svolta su un rilevato sperimentale appositamente progettato e costruito per le finalità del trattamento con calce delle terre argillose. Tale prova di campo è stata sviluppata nell’ambito dei lavori di ammodernamento di una infrastruttura di grande comunicazione in Sicilia, per consentire il reimpiego delle argille di risulta dagli scavi previsti in progetti nella costruzione delle parti in rilevato della stessa. Il programma sperimentale messo a punto si è pertanto concentrato sull’identificazione e la caratterizzazione geotecnica delle argille di scavo al fine di definire le modalità esecutive del loro trattamento con calce. Attraverso le prove in vera grandezza condotte, si è sviluppata una procedura di controllo che permette di definire le modalità di corretta esecuzione dei lavori di trattamento con calce dei terreni argillosi, con specifico riferimento alla loro caratterizzazione geotecnica, di fissare criteri e soglie prestazionali per l’accettazione delle lavorazioni in regime di qualità e di rigoroso rispetto dei principi di salvaguardia ambientale, nonché di intervenire in tempo utile per adottare correttivi in caso di derive di esecuzione. The paper presents the results of a field test carried out on an experimental embankment especially designed and built for the purposes of the lime treatment of clayey soils. This field test was carried out with the aim of studying the use of clays, resulting from excavations, as construction material for embankments for works of modernization of a large communication infrastructure in Sicily. Hence the experimental programme carried out focused on the geotechnical characterization of excavated clay in order to define the manner of implementation of clay treatment with lime. By means of full-scale tests, a monitoring procedure was developed in order to define proper execution of lime treatment of clay soils, requirements and performance thresholds being set for acceptance of working in quality system and strict observance of the principles of environmental protection, as well as to intervene in time to take corrective action in case of drifts of execution.

The work described in the paper is an experimental investigation of the effects of anisotropic stress states and histories on the small-strain shear stiffness of reconstituted clays as measured with bender element tests. A brief review is made of previous work dealing with the dependence of small-strain shear modulus on stress state and history in isotropic conditions of confinement, and the rational link that exists between void ratio, e, effective stress, σ′, and overconsolidation ratio, OCR, is considered. Under isotropic stress conditions, only two out of the three variables e, σ′ and OCR are required to describe the dependence of the small-strain stiffness of a clay on current state and history. The same approach proved useful in the analysis of the data from tests with anisotropic stress conditions. The values of the small-strain shear modulus of reconstituted samples compressed along stress paths with constant triaxial effective stress ratios were higher than those measured on isotropically compressed samples. The observed differences increased with increasing stress ratio and could be explained only in part in terms of the smaller void ratios of the anisotropically compressed samples at the same mean effective stress. Simple relationships to evaluate the stiffness indexes of clays that have undergone anisotropic stress histories are proposed. L'article décrit des recherches expérimentales sur les effets de l'état de contrainte anisotrope et des contraintes anisotropes déjà subies sur la rigidité au cisaillement d'argiles reconstituées soumises à de petites contraintes, la rigidité etant measurée a l'aide de languettes piezoelectriques vibrantes (bender elements). Il présente un aperçu de travaux antérieurs sur la variabilité du module de cisaillement, dans le cas de petites contraintes, en fonction de l'état de contrainte et des contraintes déjà subies, dans des conditions de confinement isotropes, et examine le lien rationnel entre l'indice des vides (e), la contrainte intergranulaire (σ′) et le coefficient de préconsolidation (OCR). En conditions de contrainte isotropes il suffit de connaître deux des trois variables e, et σ′ OCR pour décrire la variation de la rigidité au cisaillement de l'argile soumise à de petites contraintes en fonction de l'état de contrainte et des contraintes déjà subies. La même méthodologie s'est avérée utile pour analyser les résultats d'essais réalisés en conditions de contrainte anisotropes. Les valeurs du module de cisaillement d'éprouvettes reconstituées, comprimées le long des parcours de contrainte avec des rapports constants de contrainte intergranulaire triaxiale sont supérieures aux valeurs mesurées sur des éprouvettes à compression isotrope. Les écarts observés augmentent avec le rapport de contrainte et s'expliquent en partie par le fait que, pour une même contrainte intergranulaire moyenne, les éprouvettes à compression anisotrope ont un indice des vides moins élevé. L'article propose de simples rapports pour évaluer les indices de rigidité des argiles qui ont subi des contraintes anisotropes.

The mechanical behaviour of granular materials depends on their grading. Crushing of particles under compression or shear modifies the grain size distribution, with a tendency for the percentage of fine material to increase. It follows that the frictional properties of the material and the critical states are modified as a consequence of the changes in grain size distribution and the available range of packing densities. This paper illustrates an extended experimental investigation of the evolution of the grading of an artificial granular material, consisting of crushed expanded clay pellets under different loading conditions. The changes of grading of the material after isotropic, one-dimensional and constant mean effective stress triaxial compression were described using a single parameter based on the ratio of the areas under the current and an ultimate cumulative particle size distribution, which were both assumed to be consistent with self similar grading with varying fractal dimension. Relative breakage was related to the total work input for unit of volume. For poorly graded samples, the observed maximum rate of breakage is practically independent of initial uniformity. Further experiments at higher confining stress are required to investigate the mechanics of breakage of better graded samples.

This paper presents a new two-rigid block model for sliding gravity retaining walls. Some conceptual limitations of a direct application of Newmark's sliding block method to the case of retaining walls are discussed with reference to a simple scheme of two interacting rigid blocks on an inclined plane. In particular, it is shown that both the internal force between the blocks and their absolute acceleration are not constant during sliding, and must be computed by direct consideration of the dynamic equilibrium and the kinematic constraints for the whole system. The same concepts are extended to the analysis of the active soil wedge–wall system, leading to an extremely simple procedure for computing the relative displacements of the wall when subjected to base accelerations exceeding the critical value. A comparison with the results of numerical analyses demonstrates that the proposed method is capable of describing fully the kinematics of the soil wedge–wall system under dynamic loading. On the contrary, direct application of Newmark's method may lead to inaccurate predictions of the final displacements, in excess or in defect depending on a coefficient which emerges from direct consideration of the dynamic equilibrium of the whole system. This coefficient can be viewed as a corrective factor for the horizontal relative acceleration of the wall, related to the mechanical and geometrical properties of the soil–wall system.

he factors that contributed to the initiation of a triggering mechanism in a shallow landslides induced by rainfall are investigated in this work at laboratory scale. The aim of the work was to characterise the behaviour of the soil in triaxial tests, in the light of the possible failure mechanisms in a slope subjected to rainfall. The material study is a silty sand from a steep slope in Ruedlingen in the North-East of Switzerland, where a landslide triggering experiment was carried out. Conventional drained and undrained triaxial tests for the water phase were conducted to detect critical state conditions as well as peak shear strength as a function of confining pressure for three different water content related to the in situ one. Soil specimens with three different gravimetric water contents were exposed to stress paths simulating the in situ anisotropic compression followed by a decrease of mean effective stress at constant axial load. Possible unstable response along the stress paths analysed was investigated by means of second order work.

The present paper analyses an underground and inactive quarry of calcarenite, which belong to a localised area called Cave di calcarenite in Contrada Cuccidenna that has been recognised as a typical example of industrial archaeological heritage. The study of this typical quarry is finalised to the preservation and safe fruition of this site, which represents the history of manufacturing technologies of rocky ashlars. Rock samples from the pillars have been collected and, at first, a petrographic characterisation has been performed. The strength parameters have been estimated by means of triaxial and isotropic compression tests. Through a finite element analysis, the mechanical characterization has been then used to assess the stability and safety conditions of the structure. The influence of several parameters has been considered: e.g. mesostructure of the rock mass, shape of the underground quarry and effects, in close areas, of human interventions.

The paper presents the case history of San Fratello, a small town on the Nebrodi Mountains in Sicily rich in history and with very peculiar environmental and cultural characteristics. Both slopes of the narrow ridge where San Fratello is seated had been affected in 1754, 1922, 1986 and 2010 by very large landslides which caused the failure of a lot of buildings and historical monuments in the town. The paper illustrates the analyses carried out in the 2010 landslide and the design of stabilization works still in progress. Some problematic aspects related to the decision to safeguard San Fratello are discussed.

Deep Mixing Methods (DMMs) can be regarded as constantly evolving technologies for improving soil properties in order to satisfy predefined design requirements. Their applications are very common in geotechnical engineering and, in some cases, they can be conveniently selected instead of more traditional techniques. Despite DMMs are customarily used to strengthen soft soils like peats, clays, and silts, they can also be used very effectively in various subsoil configurations for several purposes, as, for instance, in the case of soil liquefaction prevention or cut-off/retaining walls. Even if soil mixing practice has become very consolidated in geotechnical engineering and numerous researchers in the past have tried to develop predictive equations taking into account the more relevant factors affecting the strength of DM constructions, i.e. influence of binder, soil, mixing and curing conditions, there is still no widely applicable formula for the estimation of the field strength characterized by a reasonable level of accuracy. Predictions are normally based on the mechanical behaviour of laboratory prepared mixtures, which, most of the time, significantly differ from in-situ treated soils due to the specific mixing, curing, and subsoil conditions encountered at the site. Technical standards were recently developed to provide general guidelines for the production of good quality laboratory mixed soil samples. Similarly, other codes concerning the critical deep mixing site construction aspects were introduced in several counties in order to improve the quality assurance and quality control (QA/QC) programmes conceived to verify the treatment effectiveness. However, a direct correlation between laboratory and field mixing performance is still far from being described, probably owing to the lack of a sufficient number of well documented case histories. In this research, a comparison tool between laboratory and field procedures has been tentatively deduced from energetic considerations depending on mixing efforts transferred to the soil to be treated using different devices. This thesis mainly focuses on the results of a comprehensive experimental investigation carried out on treated soil mixtures collected from several worldwide jobsites in which the Cutter Soil Mixing (CSM) technology was used. CSM, launched since 2003, is a recent and efficient system that, besides other DMMs, has the advantage of a high level of process control providing detailed information regarding the in-situ mixing method. The elaboration of these data, which significantly support the usual QA/QC procedures, has been used to define a new easily determinable site parameter closely related to the mixing efficacy, which, in turn, greatly influences the performance attained. As other DM methods, CSM produces some amount of spoil material, which is deemed to contain part of the binder introduced into the soil to activate hydration reactions once combined with both water and minerals in the ground. Since no estimation methods are available to evaluate the binder loss, an approximate amount of binding material is customarily added and mixed with the natural soil, hampering the performance prediction. To remedy this situation, a new formulation has been proposed to estimate the binder loss and to compute a more proper cement content. During the research activity, mechanical, hydraulic, mineralogical, and micro-structural tests were carried out in order to describe in detail the behaviour of the CSM treated material from different points of view and to acquire a reliable picture of the main factors affecting the relevant properties of stabilized soils. The obtained test results allowed to develop a new mathematical model for the evolution of the mechanical strength of granular and cohesive soils treated with the CSM technique as a function of the specific site conditions. The defined procedure has proved to be very effective in the major part of the case histories considered in this work.

In this paper results of a series of tests performed in a large calibration chamber (CC), consisting in the propagation of seismic shear and compression waves in dry carbonate oolitic sand from Kenya, are presented and analysed. The tests were aimed at assessing how the state parameters affect the small strain shear and constrained moduli. The tested sand was characterised by the determination of the index properties, its mineralogy and grain crushing, the latter investigated by oedometer tests. The calibration chamber houses a cylindrical specimen 1.2 m diameter and 1.5 m high. Within the specimens, reconstituted by dry pluviation at relative densities of 30% and 85%, were embedded arrays of three miniaturised geophones, used alternatively as source and receiver of seismic body waves. Shear and compression waves were propagated along the vertical, horizontal and inclined planes. By assuming a cross-anisotropic medium with a vertical axis of symmetry, the seismic tests allowed the assessment of the elastic parameters. The effects of the fabric, of the stress induced anisotropy as well as the stress history on the velocity of propagated seismic body waves are quantified and described in details. Semi-empirical correlations are calibrated; they can be used in engineering practice to analyse body wave velocity profiles measured in situ and to evaluate the state parameters and anisotropy properties of carbonate sand deposits.

Nel corso dei lavori di ammodernamento di una strada di grande comunicazione in Sicilia, si è valutata la possibilità di utilizzare come materiale di costruzione un’argilla di alta plasticità trattata con calce, proveniente dagli scavi eseguiti in una parte del tracciato. A questo scopo è stata avviata un’estesa ricerca sperimentale in laboratorio e sono state verificate le condizioni di posa in opera del materiale con la realizzazione di un rilevato sperimentale. Nella nota si illustrano i primi risultati della ricerca riguardanti: prove di taglio diretto, prove di compressione ad espansione laterale libera e misure di suzione.

Si riportano i risultati di una ricerca sull’erodibilità delle argille scagliettate varicolori compattate mediante rullo vibrante in strati con spessore iniziale di 25 cm. La sperimentazione è stata condotta sia in laboratorio su campioni prelevati da un rilevato sperimentale costruito da 20 anni, sia in situ con l’osservazione e lo studio dei processi di erosione superficiale e interna dello stesso rilevato. È stato accertato che l’erosione, in entrambi i casi, dipende fondamentalmente dal distacco e dal trasporto delle scaglie. È stato posto inoltre in luce il meccanismo di innesco dell’erosione interna che è legato alla presenza di fessure subverticali da essiccamento e dal fatto che il grado di compattazione dell’argilla nella parte inferiore del singolo strato è più basso di quello della parte superiore.

The water retention curve expressed in terms of water content or degree of saturation and suction is hysteretic, stress path dependent (on void ratio), and depends on pore network. To properly describe its evolving nature, a multimodal retention model is proposed by considering a linear superposition of two subcurves of the Van Genuchten type. The model is constructed based on PSDs obtained with Mercury Intrusion Porosimetry (MIP) data at specified initial state, and thus, is representative of this initial pore network configuration. Based on the WRC model proposed above, the evolution of parameter ¿ will be evaluated based on the microstructural evolution of the pore network. The model is validated based on a series of oedometer samples performed at constant water content and then saturated at different initial void ratio and the same water content.

The Agrigento Cathedral was built about nine centuries ago on the edge of a steep slope made up of alternating inclined layers of soft calcarenites and fine-grained soils; its behaviour has never been satisfactory especially as far as the North aisle is concerned. Many corrective measures have been attempted during its lifespan and also a few years ago. They proved invariably unsuccessful. Recent geotechnical investigations, referred to in the paper, permitted to find out that the main cause of the Cathedral distress is a sliding mechanism involving the upper zone of the slope underlying the North aisle; consequently the essential requirement for the preservation of the Cathedral is the stabilisation of the slope.

Artificial Ground Freezing (AGF) is a controllable process that can be used by engineers to stabilise temporarily the ground, provide structural support and/or exclude groundwater from an excavation until construction of the final lining provides permanent stability and water tightness. AGF is often carried out based on an observational approach, while a full understanding of the freezing process and of the generation of freezing-induced heave and settlements is still far from being achieved. In this work, the process of ground freezing is studied using a constitutive model that encompasses frozen and unfrozen behaviour within a unified effective-stress-based framework and employs a combination of ice pressure, liquid water pressure and total stress as state variables. The parameters of the constitutive model are calibrated against experimental data obtained from samples retrieved during construction of Napoli underground, in which AGF was extensively used to excavate in granular soils and weak fractured rock below the ground water table.

In the Valle dei Templi in Agrigento seven Doric temples stand lengthwise the crest of a rigid calcarenite cuesta over a layer of carbonate sand which lies along a thick stratum of clays. The environment is highly prone to landslides since topplings of calcarenite blocks often occur. The rock slopes are moving back and the slope edge draw near to the foundation of the Temple of Hera Lacinia contributing to increase their perilous condition. To assess the role of unsaturated sands in the instability processes, after the compositional and textural analysis of the material, direct shear tests and oedometer tests have been carried out on sand samples initially at the natural state, with low or very low values of natural water content, and finally at full saturation. The mechanical behaviour of sands seems one of the main causes of the instability influenced by the presence of an open metastable structure, which develops through bonding mechanisms generated via suctions and/or through cementing material such as clay or salts.