Thermo-poro-mechanical analysis of landslides: from creeping behaviour to catastrophic failure

The scope of the paper encompasses planar and compound sliding motions, which may exhibit creeping behaviour during a certain period but may evolve to a very rapid motion. Thermo-mechanical interactions, at the scale of the sliding surface, are accepted as a critical aspect to explain these motion phases and their relationship. The sliding kinetics and global equilibrium are described at a large scale and the evolving shearing strength at the sliding surface derives from the local analysis of the shearing band and its vicinity. Pore pressures, temperatures and related variables are calculated by resolving a set of balance equations. The paper describes the transition from creeping motions to a rapid event. Results are found in terms of dimensionless numbers. Calculation of the slide evolution requires special numerical techniques described in the paper. Band permeability is found to be the dominant property controlling the triggering of fast motions. The creeping stage and the eventual slide blow-up are intimately linked. This relationship is explored in the paper. The models presented can be readily used to back-analyse relevant case histories or, in principle, even to carry out predictive modelling, provided an adequate calibration is available for the material parameters

An investigation into the effect of particle platyness on the strength of granular materials using the discrete element method

It has long been recognised that the macroscopic mechanical behaviour of a granular material depends, to differing extents, on micro-mechanical properties such as the particle size distribution, the particle shape, the inter-particle friction angle and the particle strength. However, a systematic investigation of some of these effects is still lacking. In this paper we focus on particle shape, which is one of the fundamental characteristics of a granular material. We build on previous work that used the axes of an equivalent scalene ellipsoid to characterise particle form, one of the three aspects that define particle shape. (The other two being angularity and roughness.) We use DEM simulations to investigate the effect of particle form, and in particular of particle platyness, on the friction angle of a granular material at critical state. It is found that a deviation of particle shape from that of a sphere leads to higher angles of friction; quantities such as fabric, average rates of particle rotation and interparticle sliding are used to provide insights into the underlying micromechanics

Modelling scheme for railway vehicle/track/ground dynamic interaction in the time domain

Modelling of vehicle/track/ground dynamic interaction is an important issue for railway design. Better understanding of how the moving dynamic loads are distributed through the track components to the ground can be derived from these numerical results to improve the stability of the moving train and decrease the cost of the maintenance. Nonlinear models of the ground may be required due to the large displacements induced by heavier and/or high-speed trains. The aim of this research is to develop a general modelling approach for predicting the dynamic behaviour for a variety of situations. A three-dimensional vehicle/track/ground approach in the time domain is presented. The finite element method is used to model the track/ground vibration. The equations of motion of a multi-body vehicle are implemented to couple with the ground/track system. An alternative approach to the commonly used infinite elements is proposed for modelling the far-field, based on the use of mass-proportional damping to suppress the reflections from model edges. Improved results are shown and better efficiency can be found compared to the results from models with infinite elements. Furthermore, two different geometries for the ground model, a hemispherical and a cuboid one, are discussed. The issue of transients developed by the moving load is discussed and it is shown that long models are required for load speeds close to the wavespeed in the ground to allow the results to achieve steady state. Finally, the results are benchmarked against the results from a wavenumber FE/BE model

What causes large submarine landslides on low gradient (

Submarine landslides can cause damaging tsunamis, the height of which scales up with the volume of the displaced mass. The largest underwater landslides are far bigger than any landslides on land, and these submarine mega-slides tend to occur on open continental slopes with remarkably low gradients of less than 2°. For geohazard assessments it is essential to understand what preconditions and triggers slope failure on such low gradients. Previous work has suggested that generation of high excess pore pressure due to rapid sediment deposition plays a key role in such failures. However, submarine slope failure also occurs where sedimentation rates are low (<0.15 m/ky), such as off north-west Africa. We use a fully coupled stress and fluid flow finite element model to test whether such low sedimentation rates can generate sufficient excess pore pressures to cause failure of a 2° slope. The sensitivity of overpressure generation and slope stability is assessed with respect to different sedimentation rates and patterns, sediment consolidation properties and stratigraphic layer configurations. The simulations show that in general it is difficult to generate significant excess pore pressure if sediment accumulation is slow and the only pressure source. However, we identify a sediment compression behavior that can lead to submarine landslides in locations worldwide. Our results imply that compressibility is an important factor for the stability of low gradient continental slopes

On the use of Reuleaux plasticity for geometric non-linear analysis

Three dimensional analyses including geometric and material non--linearity require robust, efficient constitutive models able to simulate engineering materials. However, many existing constitutive models have not gained widespread use due to their computational burden and lack of guidance on choosing appropriate material constants. Here we offer a simple cone-type elasto-plastic formulation with a new deviatoric yielding criterion based on a modified Reuleaux triangle. The perfect plasticity model may be thought of as a hybrid between Drucker-Prager (D-P) and Mohr-Coulomb (M-C) that provides control over the internal friction angle independent of the shape of the deviatoric section. This surface allows an analytical backward Euler stress integration on the curved surface and exact integration in the regions where singularities appear. The attraction of the proposed algorithm is the improved fit to deviatoric yielding and the one--step integration scheme, plus a fully defined consistent tangent. The constitutive model is implemented within a lean 3D geometrically non-linear finite-element program. By using an updated Lagrangian logarithmic strain--Kirchhoff stress implementation, existing infinitesimal constitutive models can be incorporated without modification

Assessment of invitrosynergy of daptomycin or vancomycin plus ceftaroline for daptomycin non-susceptible Staphylococcus aureus

The combination of vancomycin or daptomycin plus ceftaroline has showed synergistic results in vitro. This study aimed to investigate in vitro synergy of vancomycin or daptomycin plus ceftaroline for seven patients with daptomycin non-susceptible Staphylococcus aureus (SA) bacteremia Thirteen isolates from seven patients were evaluated: two methicillin-susceptible and five methicillin-resistant SA infections. All patients were treated with daptomycin and became non-susceptible (minimum inhibitory concentration (MIC) \u3e1 μg/mL) with therapy or had resistant strains initially. Time kill experiments were completed with 0.25 × MIC, 0.5 × MIC, and 0.75 × MIC concentrations. No synergy was seen at 0.25 × MIC. Synergy was observed for 4 isolates with vancomycin plus ceftaroline and with daptomycin plus ceftaroline for 2 isolates at 0.5 × MIC. These results are in accordance with literature that supports synergistic combinations of daptomycin or vancomycin with ceftaroline for SA bacteremia. Daptomycin non-susceptible SA bacteremia presents a treatment challenge

Desalination using renewable energy sources on the arid islands of South Aegean Sea

Water and energy supply are strongly interrelated and their efficient management is crucial for a sustainable future. Water and energy systems on several Greek islands face a number of pressing issues. Water supply is problematic as regards both to the water quality and quantity. There is significant lack of water on several islands and this is mainly dealt with tanker vessels which transport vast amounts of water from the mainland. At the same time island energy systems are congested and rely predominanty on fossil fuels, despite the abundant renewable energy potential. These issues may be addressed by combining desalination and renewable energy technologies. It is essential to analyse the feasibility of this possibility. This study focuses on developing a tool capable of designing and optimally sizing desalination and renewable energy units. Several parameters regarding an island's water demandand the desalination's energy requirements are taken into account as well as input data which concern technological performance, resource availability and economic data. The tool is applied on three islands in the South Aegean Sea, Patmos (large), Lipsoi (medium) ad Thirasia (small). Results of the modelling exercise show that the water selling price ranges from 1.45 euro/m^3 for the large island, while the corresponding value is about 2.6 euro/m^3 for the small island, figures significantly lower than the current water cost (7-9 euro/m^3)

Flatness-Based Control Approach to Drug Infusion for Cardiac Function Regulation

A new control method based on differential flatness theory is developed in this study, aiming at solving the problem of regulation of haemodynamic parameters. Actually control of the cardiac output (volume of blood pumped out by heart per unit of time) and of the arterial blood pressure is achieved through the administered infusion of cardiovascular drugs such as dopamine and sodium nitroprusside. Time delays between the control inputs and the system's outputs are taken into account. Using the principle of dynamic extension, which means that by considering certain control inputs and their derivatives as additional state variables, a state-space description for the heart's function is obtained. It is proven that the dynamic model of the heart is a differentially flat one. This enables its transformation into a linear canonical and decoupled form, for which the design of a stabilising feedback controller becomes possible. The proposed feedback controller is of proven stability and assures fast and accurate tracking of the reference setpoints by the outputs of the heart's dynamic model. Moreover, by using a Kalman filter-based disturbances' estimator, it becomes possible to estimate in real-time and compensate for the model uncertainty and external perturbation inputs that affect the heart's model. © The Institution of Engineering and Technology

The epidemiology of pseudallescheriasis complicating transplantation: Nosocomial and community‐acquired infection

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141586/1/myc1990336296.pd