Mathematical capture of failure processes in elastoplastic geomaterials

Abstract This paper discusses a strategy to identify failure conditions in geomaterials simulated by elastoplastic constitutive laws. The main objective is to express different forms of failure through the same formalism. For this purpose, we use a set of material instability indices combining the concepts of loss of controllability and critical hardening modulus with a simple, but versatile, elastoplastic model for soils and soft rocks. This choice has allowed us to (i) compute the instability indices in analytical form, (ii) capture the implications of non-normality and prior deposition/lithification history and (iii) inspect a broad range of failure modes (e.g., brittle and ductile failure, static liquefaction and compaction banding). It is shown that, although each mode of failure has its own specific features, they can all be encapsulated in a unified mathematical representation. To obtain these results, the instability moduli must reflect the static/kinematic constraints that generate the failure process at stake. Thus, the instability indices are expressed as functions of both the hardening modulus and additional terms of kinematic origin, with the latter terms reflecting a control-dependence of the plastic response. Such results describe a procedure for achieving a unified definition of failure in elastoplastic geomaterials, which is closely linked to the theory of controllability and encompasses the intuitive notions of 'hardening' and 'softening' as particular cases

An Approach for Rotational Hardening in Geotechnical Modelling

Abstract The object of this paper is the definition of a purely kinematic rotational approach for the elastoplastic modelling of soils. Once the shape of the yield and plastic potential surfaces is assigned, their rotational kinematics in the stress space is ruled by a second order tensor directed along their surface axes. The proposed approach differs from others proposed in literature since it does not introduce any distortion of the surface and is suitable for the description of inherent or induced anisotropy as well as the behaviour of soils subjected to cyclic loading

Caratterizzazione mediante tecniche di imaging a risonanza magnetica nucleare dello spiazzamento di fluidi non miscibili nei mezzi porosi

L’attività condotta in questo lavoro di tesi è stata rivolta alla caratterizzazione delle proprietà petrofisiche di campioni di roccia, mediante tecniche di imaging a risonanza magnetica (MRI). In particolare il lavoro si è focalizzato sullo studio dello spiazzamento di fluidi non miscibili in campioni di roccia per caratterizzarne le proprietà intrinseche, quale la permeabilità, e al contempo verificare il comportamento del fluido all’interno del mezzo poroso. Le prove di laboratorio classiche, sono state eseguite tramite cella triassiale collegata ad un apparato di flussaggio per determinare le proprietà di trasporto della roccia. Tale apparato, ha permesso anche l’applicazione di metodi a risonanza magnetica nucleare (NMR) per ottenere in modo non invasivo e non distruttivo indicazioni di carattere qualitativo sui mezzi porosi esaminati, attraverso la realizzazione di immagini create col tomografo Artoscan Esaote. Per analizzare le immagini acquisite, in modo anche quantitativo, è stato necessario utilizzare diversi software sviluppati ad hoc. In particolare si menziona il software ARTS per la comparazione quantitativa delle immagini e CorrelaIMG per misurare in modo oggettivo, l’avanzamento del fronte di spiazzamento. Tali analisi,sono state completate su due campioni rocciosi di differente litotipo. L’avanzamento del fronte, per ambedue i campioni, è risultato essere ben descrivibile mediante un semplice modello esponenziale. Il valore dei parametri del modello sono stati valutati mediante regressione non lineare col risolutore Solver di Excel®. I risultati ottenuti mostrano una piena corrispondenza fra le misure classiche e i risultati ottenuti per mezzo delle immagini MRI. Pertanto, il lavoro di tesi riconferma,come la tecnica MRI sia un ottimo strumento, per valutare le caratteristiche di un mezzo poroso sottoposto a flussaggio, specialmente quando si renda indispensabile minimizzare le alterazioni subite dal campione come conseguenza della tecnica adottata

A Computationally Efficient Method to Determine the Probability of Rainfall-Triggered Cut Slope Failure Accounting for Upslope Hydrological Conditions

We present a new computationally efficient methodology to estimate the probability of rainfall-induced slope failure based on mechanical probabilistic slope stability analyses coupled with a hydrogeological model of the upslope area. The model accounts for: (1) uncertainty of geotechnical and hydrogeological parameters; (2) rainfall precipitation recorded over a period of time; and (3) the effect of upslope topography. The methodology provides two key outputs: (1) time-varying conditional probability of slope failure; and (2) an estimate of the absolute frequency of slope failure over any time period of interest. The methodology consists of the following steps: first, characterising the uncertainty of the slope geomaterial strength parameters; second, performing limit equilibrium method stability analyses for the realisations of the geomaterial strength parameters required to calculate the slope probability of failure by a Monte Carlo Simulation. The stability analyses are performed for various phreatic surface heights. These phreatic surfaces are then matched to a phreatic surface time series obtained from the 1D Hillslope-Storage Boussinesq model run for the upslope area to generate Factor of Safety (FoS) time series. A timevarying conditional probability of failure and an absolute frequency of slope failure can then be estimated from these FoS time series. We demonstrate this methodology on a road slope cutting in Nepal where geotechnical tests are not readily conducted. We believe this methodology improves the reliability of slope safety estimates where site investigation is not possible. Also, the methodology enables practitioners to avoid making unrealistic assumptions on the hydrological input. Finally, we find that the time-varying failure probability shows marked variations over time as a result of the monsoon wet–dry weather

Influence of Inter-Particle Friction and Damping on the Dynamics of Spherical Projectile Impacting Onto a Soil Bed

This study investigates the dynamics of a spherical projectile impact onto a granular bed via numerical simulations by discrete element method (DEM). The granular bed is modeled as an assembly of polydisperse spherical particles and the projectile is represented by a rigid sphere. The DEM model is used to investigate the cratering process, including the dynamics of the projectile and energy transformation and dissipation. The cratering process is illustrated by tracking the motion of the projectile and granular particles in the bed. The numerical results show that the dynamics of the projectile follows the generalized Poncelet law that the final penetration depth is a power-law function of the falling height. The numerical results can match well the experimental data reported in the literature, demonstrating the reliability of the DEM model in analyzing the impact of a spherical projectile on a granular bed. Further analyses illustrate that the impact process consists of three main stages, namely the impact, penetration and collapse, as characterized by the evolution of projective velocity, strong force chains and crater shape. The initial kinetic and potential energy of the projectile is dissipated mainly by inter-particle friction which governs the projectile dynamics. The stopping time of projectile decreases as the initial impact velocity increases. The final penetration depth scales as one-third the power of total falling height and is inversely proportional to the macroscopic granular friction coefficient.National Natural Science Foundation of China (No. 42107155), the Royal Society, Sino-British Fellowship Trust International Exchanges Award (No. IES\R2\202023), the Fundamental Research Funds for the Central Universities (No. 2682021CX061), the National Key R&D Program of China (No. 2017YFC1502500

Small bowel intussusception from renal cell carcinoma metastasis : a case report and review of the literature

Abstract Background: Renal cell carcinoma is the most frequent malignant neoplasia of the kidney accounting for 90 % of all renal solid tumors. Metastases from renal cell carcinoma are rarely located in the small bowel and generally their clinical presentation includes bleeding and obstruction. Intussusception in adults is an extremely rare pathological condition and only 30 to 35 % of small bowel intussusceptions are derived from malignant lesions. Case presentation: We report here a clinical case of a 75-year-old white man hospitalized for anemia and subocclusion. An abdominal ultrasound and computed tomography showed a small bowel intussusception. During a surgical exploration, a polypoid lesion was found to be the lead point of the intussusception. His small intestine was resected and a functional side-to-side anastomosis was performed. The histological features of the surgical specimen confirmed the diagnosis of metastatic renal cell carcinoma. Conclusions: Small bowel intussusception from renal cell carcinoma metastasis should always be considered in the setting of unexplained intestinal subocclusion in patients with a history of renal cell carcinom

First evidence of wulfenite in Calabria Region (Southern Italy)

This data article contains mineralogical and chemical data of the wulfenite (PbMoO4) sampled from mine of Fiumarella in Calabria region (Southern Italy). Wulfenite is a rare mineral belonging to the class of minerals called molybdates and if found in large amounts it can be used for the extraction of molybdenum. In the mine of Fiumarella, in addition to primary minerals such as barite, galena, cerussite, anglesite, fluorite and chalcopyrite, wulfenite was also detected. Wulfenite crystals are bipyramidal, few microns in size and grow as single crystals that can reach 1 mm. Methods for obtaining the data sets include optical microscopy, micro X-Ray Fluorescence and micro-Raman spectroscopy

The optical links for the trigger upgrade of the Drift Tube in CMS

The first phase of the upgrade of the electronics of Drift Tubes (DT) in the CMS experiment is reported. It consists of the translation of the readout and trigger data from electrical into optical and their transmission from the CMS experimental cavern to the counting room. Collecting the full information of the DT chambers in the counting room allows the development of new trigger hardware and algorithms

Bioinformatics Solutions for Image Data Processing

In recent years, the increasing use of medical devices has led to the generation of large amounts of data, including image data. Bioinformatics solutions provide an effective approach for image data processing in order to retrieve information of interest and to integrate several data sources for knowledge extraction; furthermore, images processing techniques support scientists and physicians in diagnosis and therapies. In addition, bioinformatics image analysis may be extended to support several scenarios, for instance, in cyber-security the biometric recognition systems are applied to unlock devices and restricted areas, as well as to access sensitive data. In medicine, computational platforms generate high amount of data from medical devices such as Computed Tomography (CT), and Magnetic Resonance Imaging (MRI); this chapter will survey on bioinformatics solutions and toolkits for medical imaging in order to suggest an overview of techniques and methods that can be applied for the imaging analysis in medicine

A Macroelement Approach for the Stability Assessment of Trees

Interaction diagrams in the generalized 3D loading space of vertical (V), horizontal (H) and moment (M) actions constitute the basis of the design of foundation structures in case of complex loads combinations. The mechanical response of such systems is frequently interpreted in terms of the ‘macroelement’ theory, where a generalized incremental constitutive relationship is introduced, linking the displacements and rotations of the foundation (playing the role of generalized strains) to the histories of applied loading components (i.e. the generalized stresses). In this paper an attempt to extend a classical macroelement framework, to the case of root-soil interaction presented. The model is calibrated on small scale experimental data on 3D printed plastic root systems, subject to combined V-H-M loads, and a parametric analysis on the main governing parameters is discussed. The comparison between numerical and experimental data suggests that the macroelement approach could be an efficient and simple analytical tool for describing the whole moment-rotation curve, overcoming the main simplifying hypotheses currently employed in arboriculture practice