Search

Submarine buried pipelines are often laid in trenches backfilled with loose sandy soil, which is intrinsically prone to liquefaction. When liquefaction is triggered, the soil tends to behave as a viscous fluid with vanishing shear strength and very limited ability to restrain structural displacement, for instance during the occurrence of pipeline flotation. Recently, a 2D CFD-based approach for the analysis of pipe flotation in liquefied sand has been proposed by Pisano et al. (2020), in which soil reconsolidation effects are phenomenologically captured by considering rheological parameters that evolve in space and time as pore water pressures dissipate. Despite a remarkable agreement with experimental data from the literature, the complexity and computational costs of such approach may still hinder its applicability to pipeline engineering practice. To overcome this limitation, a simplified model is proposed herein, in which all the forces governing the motion of the pipe are expressed via simple analytical relationships. After thorough validation against 2D CFD results and relevant experimental data, it is concluded that the new simplified model largely retains the predictive capability of Pisano et al.’s framework in combination with negligible computational costs.

Knowledge of the in situ stress state of rock mass is fundamental for engineering, geological and geophysical applications. In situ stress state determination requires in principle the evaluation of the three principal stresses and the related principal directions, but it is widely recognized in the literature that the maximum horizontal stress is the most difficult component to accurately estimate. In the context of borehole methods, this paper proposes a step-by-step analytical procedure to estimate some bounds to the maximum horizontal stress, starting from a geomechanical description of the rock and relying on information generally available in the engineering practice. The procedure is divided in substeps, each one requiring additional information about the mechanical properties of the rock and on the geometrical properties of the failed portion of rock: more information available implies a lower uncertainty on in situ stress estimate. Furthermore, since the proposed procedure is analytical, it allows a complete and very easy implementation in a spreadsheet. The aim of the work is thus to provide a rigourous but simple analytical tool that can be used in engineering practicte to estimate some bounds to the maximum horizontal in situ stress state. The approach is finally validated by means of both numerical simulations, performed with a sophisticated numerical tool, and experimental field data coming from the literature.

We present a simplified model of damaging porous material, obtained through consistent linearization from a recursive-faulting material model described in (Pandolfi et al. 2016). The brittle damage material model is characterized by special planar micro-structures, consisting of nested families of equi-spaced frictional-cohesive faults in an otherwise elastic matrix material. The linear kinematics model preserves the main microstructural features of the finite kinematics one but offers a far better computational performance. Unlike models commonly employed in geo-mechanical applications, the proposed model contains a small number of parameters, to wit, two elastic moduli, three frictional-cohesive parameters, and three hydraulic response parameters, all of which having clear physical meanings and amenable to direct experimental measurement through standard material tests. The model is validated by comparison to triaxial hydro-mechanical experimental data. Despite the paucity of material constants, the salient aspects of the observed behavior are well captured by the model, qualitatively and quantitatively. As an example of application of the model, we simulate the excavation of a borehole in a rocky embankment.

Constitutive models of unsaturated soils, and in particular those based on constitutive variables which include both degree of saturation and suction, are characterised by strong non linearities due to hydromechanical coupling. In this paper, a refined Runge–Kutta–Dormand–Prince explicit algorithm and a fully implicit Euler scheme are compared for the integration of the latter class of models. The explicit and implicit procedures have been tested along different hydromechanical paths, involving various hydraulic and mechanical external control conditions. Accuracy and efficiency of the algorithms have been investigated. The results confirm that substepping is mandatory for the explicit algorithm to converge regardless the initial step size and to remain sufficiently accurate. The value of the incremental hydromechanical work per unit volume was calculated during the explicit integration procedure. The numerical results show that the maximum size of the substep which can be adopted to meet a given tolerance depends on the gradient of the incremental work per unit volume. Therefore, the latter appears a good candidate to identify problematic integration steps in terms of convergence. Accuracy of the implicit algorithm also depends on the chosen step size, although the algorithm proved to be convergent in all the paths analysed.

Knowledge of the in situ stress state in rock and soil deposits is very important in many problems in civil, mining and petroleum engineering and energy development, as well as in geology and geophysics. The prediction of the response of rock masses interacting with underground structures is highly influenced by the stress field. For example, as pointed out in [1], in civil and mining engineering, in situ stresses control the distribution and magnitude of the stresses around underground openings such as tunnels, mines, shaft or caverns. Stress concentrations in the excavation walls may be large enough to overstress the rock, mobilize the strength of the rock mass and induce failure. On the other hand, tensile stresses in excavation walls may open existing fractures or create new ones which could result in block stability problems. An exact prediction of in situ stress acting over a rock mass, together with its spatial variation, is a very complex topic; the current stress state is a mixed consequence of tectonic conditions and of mechanical effects due to local thermochemo-hydraulic conditions. Due to the complex nature of rocks and rock masses, the stress field is rarely homogeneous and also its time evolution can be significant within a geological formation. Stress state is a symmetric second-order tensor and so it is defined by six independent components, e.g. the three principal stresses and the three principal directions. Stresses in rocks cannot be measured directly and can only be inferred by disturbing the rock. Amadei and Stephansonn [2] presented a detailed summary of the available sources of information from which it is possible to obtain the in situ stress state, involving hydraulic methods (i.e. hydraulic and sleeve fracturing), relief methods, jacking methods, strain recovery methods, borehole failure methods as well as fault-slip data analysis and earthquake focal mechanisms. Zoback [4] proposed an overview of a possible strategy to characterize the stress field: the vertical stress can be determined from the equilibrium in the vertical direction, i.e. by integration of the density logs, while observations of the geometrical arrangement of drilling-induced tensile fractures are an effective way to check whether the vertical stress is a principal stress. The orientation of the other principal stresses can be determined from wellbore observations, recent geologic observations and earthquake focal mechanisms, as well as from stress recovery methods. The magnitude of the minimum principal stress can be estimated from the analysis of hydraulic fracturing and leak-off tests, while the pore pressure can be either measured directly or estimated with some caution from geophysical logs or seismic data. In this paper the vertical stress is assumed to be a principal stress, so that the remaining two directions are supposed to be horizontal. This assumption is reliable for non-active regions or regions already relaxed from the previous tectonical stress. As pointed out by Bell [3], the free surface of sedimentary basins is generally horizontal, so that the principal stress directions are, to a good approximation, horizontal and vertical. From a practical point of view, if the vertical direction is assumed to be a principal one, it is sufficient to know just a horizontal principal direction, since the remaining one is orthogonal to the plane on which the other two are lying. Throughout the paper, Sv will represent the principal vertical in situ stress, SH represents the maximum horizontal in situ stress and Sh represents the minimum horizontal in situ stress, whose magnitude can be evaluated through hydraulic fracturing or leak off tests (except for reverse faulting regimes). Assuming that Sv and Sh are known, the aim of the note is to present a methodology for the definition of some boundaries for

Because of their mineralogy, active clays are very sensitive to changes in the type and concentration of species dissolved in the pore water. At a molecular level, this sensitivity can be explained by variations in the short range interaction forces acting between clay platelets immersed in the pore water. While models based on equilibrium of short range interaction forces can be used to predict the volumetric behavior of dilute clay suspensions, different approaches must be invoked for real soils. Natural and compacted soils react differently from dilute suspensions to chemical changes because of their fabric. It is, therefore, not possible to derive reliable relationships (at least from the quantitative point of view) describing the chemo-mechanical behavior of active soils solely on the basis of mineralogical and chemical properties. Both microscopic experimental evidences and modeling approaches are used here to analyze the effects imparted by fabric on the coupled hydro-chemo-mechanical behavior of an active clay soil.

The electrical conductivity of a soil can be related to the electrical conductivity of its solid and fluid constituents by means of theoretical and empirical relationships, taking into account the effect of porosity, saturation degree, fabric and clay content. Hence monitoring the evolution of the electrical conductivity inside a soil sample can provide useful information concerning the progress of hydro-chemomechanical processes and the subsequent effects on both soil skeleton and pore water. With this aim a laboratory apparatus for 3D electrical resistivity tomography has been recently developed. Some applications of this apparatus to the monitoring of different geotechnical processes in which the knowledge of the water content and of ionic concentration is particularly relevant are presented.

In the last decade, RFID systems have gained increasing popularity, but they also pose many critical security concerns. The most challenging security threat in several RFID applications is tag cloning. In this paper, we do not focus on preventing tag cloning, but propose the application of the intrusion detection model to identify when tag cloning has occurred. In particular, we present an ontology-based misuse detection system (IDS) that integrates information coming from RFID middleware layer to detect tag cloning. Ontologies and rules are applied to formalize the declarative and procedural knowledge required to implement a "track & trace" technique, with the final aim of modelling two levels of detection against tag cloning. An inference engine is used to provide the proposed IDS with the advanced capacity of automatically reasoning about ontologies and rules in order to actually apply the formalized model of detection and infer when a tagged object is cloned or victim of a cloning attack. © Springer Science+Business Media B.V. 2010.

Pervasive Computing technologies can be successfully used in hospital and clinical environments in order to provide smart and enhanced healthcare services and applications. According to this vision, the paper presents an RFID-based application for handling the workflow of patients injected with radioactive substances in a nuclear medicine department. Specifically, the application exploits the RFID technology to provide automatic and non-intrusive mechanisms for i) guaranteeing the appropriateness of the clinical workflow of the injected patients and ii) accessing all the clinical information of the injected patients by automatically querying the radiological information systems.