Fibre-reinforced sand::interaction at the fibre and grain scale

For fibre-reinforced granular soils, the efficiency of the fibres is governed by the local fibre–grain interaction mechanism. This local interaction mechanism is evaluated, in this paper, by using a modified version of the shear-lag stress theory. While this theory provides a description of the stress-transfer mechanism at fibre–matrix interface level, it also generates the stress distribution along the fibre. The proposed model explicitly accounts for the effects of the geometrical fibre and granular size characteristics, fibre stiffness, global stress level, soil density and the non-linearity of soil behaviour. An analytical expression for the ratio of strains in the fibre and in the composite, which is fundamental for any prediction of fibre contribution, is further derived. A discussion on the effects of the controlling parameters is presented, while the scale-up of the problem at the composite level is then conducted by using a continuum constitutive model appropriately modified to account for the strain ratio between the fibre and the composite. The model is validated against a series of triaxial compression tests on two different sands mixed with polypropylene fibres of different aspect ratios. </jats:p

Elasto-plastic model for sand including time effect

Time effects on granular soils have been observed in the laboratory and by in-situ tests, but these cannot be reproduced by classical elasto-plastic models. To address these concerns, existing specific modelling approaches were based on the theory of viscoplasticity formulated by Perzyna or on a viscous evanescent relationship. This work explores an alternative elasto-plastic modelling framework formulated in a multiaxial structure space. The proposed elasto-plastic model is associated with a thixotropic-type framework through the use of a structure parameter, the evolution of which illustrates the competition between two effects: the time-dependent tendency of the granular system to reach its stable configuration - restructuration - and its destructuration under external perturbations. The structure parameter is linked to the existence of a stress-dependent target structure towards which the current granular material structure evolves. The timescale is explicitly introduced by postulating a rate for this structure evolution. The modelling of the material behaviour has shown good similarities with the response of granular soils observed in monotonic loading, as well as during creep and variable strain rate loading experiments

An evaluation of non-linear undrained behaviour in the moderate strain range for fine-grained soils

To select appropriate stress-strain parameters for serviceability limit state calculations, an understanding is needed of the likely variation of stress-strain behaviour within the model displacement mechanism. One approach that may be utilised to investigate variations in stress-strain behaviour is by employing a simple non-linear model (with a small number of physically significant parameters) that simulates experimental measurements of soil stress-strain with reasonable precision. By testing the sensitivity of the model parameters to changes in physical properties that can be expected to be related to them the reliability of different models can be established. Recently, empirical analysis of the published triaxial test database RFG/TXCU-278 identified a significant positive correlation between γ50 and OCR for four test modes (CIUC, CIUE, CKUC and CKUE). In this paper, a new experimental dataset from a programme of reconstituted soil tests on Kaolin and Bothkennar Clay is used to investigate the validity of a simple non-linear model

Comparison of simple stress-strain models in the moderate strain range for fine-grained soils:A review

The prediction of stress-strain behaviour in soils is a problem that can be approached in different ways depending on the design scenario. In some cases, a multi-parameter constitutive model calibrated with non-routine soil tests may be appropriate, for example, where a model has been developed for the relevant soil at a building site subject to complex loading. However, simple characteristic parameters are desirable for examining the variability of soil behaviour especially at regional scales. This paper describes a method of assessing the suitability of simple models for simulating non-linear undrained soil stress-strain behaviour in the moderate strain range. The moderate strain range is defined by a soil strength mobilisation of 20% to 80%. Three simple stress-strain models are compared. A published database of reconstituted triaxial tests is used to evaluate the three models with selected statistical tools that quantify errors associated with the simple model approximation of the relationship between stress and strain. The paper discusses the value of computing the model error and the trade off to make between introducing a greater number of parameters (and tests) for model precision and limiting the complexity of the variability characterisation

FORMALIZATION OF THE CULTURAL HERITAGE MANAGEMENT MODEL AS A FACTOR OF TOURISM DEVELOPMENT IN THE RUSSIAN FEDERATION

The article formalizes the model of cultural heritage management, clarifies the content of cultural heritage cognition by considering the processes of studying, preserving and using cultural heritage objects as a factor in the development of tourism in the Russian Federation, taking into account modern challenges and opportunities. The preservation of cultural heritage and its rational use have a key role and importance for attracting tourist flows and improving socio-economic indicators and sustainable development of the region. In this regard, the importance of highlighting the internal structure of the cultural heritage management process as a factor in the development of tourism in the Russian Federation is actualized. The purpose of the study: to formalize the model of cultural heritage management as a factor of tourism development in the Russian Federation. The research methodology is represented by a set of general scientific and special historical methods of scientific cognition, the principles of historicism, scientific, systematic and complex. The scientific novelty consists in an attempt to comprehensively comprehend the problem of studying, preserving and using Russian cultural heritage objects based on the analysis of contemporary research on the subject, taking into account modern realities and formalizing the model of cultural heritage management as a factor in the development of tourism. The model of cultural heritage management as a factor of tourism development in the Russian Federation is formalized. The main reserves for improving the efficiency of cultural heritage management as a factor of tourism development are improving the quality of tourist products in the field of cultural and educational tourism; combining material and intangible parts of cultural heritage; developing eventfulness in the regions; creating an authentic environment in Russian tourist locations; branding cultural heritage sites and territories of their placement; using a wide range of digital technologies to promote and involve cultural heritage objects in the tourism industry; training professional personnel to work in the cultural and educational tourism industry

Micromechanics of seismic wave propagation in granular materials

In this study experimental data on a model soil in a cubical cell are compared with both discrete element (DEM) simulations and continuum analyses. The experiments and simulations used point source transmitters and receivers to evaluate the shear and compression wave velocities of the samples, from which some of the elastic moduli can be deduced. Complex responses to perturbations generated by the bender/extender piezoceramic elements in the experiments were compared to those found by the controlled movement of the particles in the DEM simulations. The generally satisfactory agreement between experimental observations and DEM simulations can be seen as a validation and support the use of DEM to investigate the influence of grain interaction on wave propagation. Frequency domain analyses that considered filtering of the higher frequency components of the inserted signal, the ratio of the input and received signals in the frequency domain and sample resonance provided useful insight into the system response. Frequency domain analysis and analytical continuum solutions for cube vibration show that the testing configuration excited some, but not all, of the system’s resonant frequencies. The particle scale data available from DEM enabled analysis of the energy dissipation during propagation of the wave. Frequency domain analysis at the particle scale revealed that the higher frequency content reduces with increasing distance from the point of excitation

Construction of simplified design <i>p-y</i> curves for liquefied soils

In practice, laterally loaded piles are most often modelled using a ‘Beam-on-Nonlinear-Winkler-Foundation’ (BNWF) approach. While well calibrated p-y curves exist for non-liquefied soils (e.g. soft clay and sands), the profession still lacks reliable p-y curves for liquefied soils. In fact, the latter should be consistent with the observed strain-hardening behaviour exhibited by liquefied samples in both element and physical model tests. It is recognised that this unusual strain-hardening behaviour is induced by the tendency of the liquefied soil to dilate upon undrained shearing, which ultimately results in a gradual decrease of excess pore pressure and consequent increase in stiffness and strength. The aim of this paper is twofold. First it proposes an easy-to-use empirical model for constructing stress-strain relationships for liquefied soils. This only requires three soil parameters which can be conveniently determined by means of laboratory tests, such as a cyclic triaxial and cyclic simple shear tests. Secondly, a method is illustrated for the construction of p-y curves for liquefiable soils from the proposed stress-strain model. This involves scaling of stress and strain into compatible soil reaction p and pile deflection y, respectively. The scaling factors for stress and strain axis are computed following an energy-based approach, analogous to the upper-bound method used in classical plasticity theory. Finally, a series of results from centrifuge tests are presented, whereby p-y curves are back-calculated from available experimental data and qualitatively compared with that proposed by the authors

Role of B lymphocytes in the infarcted mass in patients with acute myocardial infarction

Despite early reperfusion, patients with ST segment elevation myocardial infarction (STEMI) may present large myocardial necrosis and significant impairment of ventricular function. The present study aimed to evaluate the role of subtypes of B lymphocytes and related cytokines in the infarcted mass and left ventricular ejection fraction obtained by cardiac magnetic resonance imaging performed after 30 days of STEMI. This prospective study included 120 subjects with STEMI submitted to pharmacoinvasive strategy. Blood samples were collected in subjects in the first (D1) and 30th (D30) days post STEMI. The amount of CD11b+ B1 lymphocytes (cells/ml) at D1 were related to the infarcted mass (rho = 0.43; P=0.033), measured by cardiac MRI at D30. These B1 cells were associated with CD4+ T lymphocytes at D1 and D30, while B2 classic lymphocytes at day 30 were related to left ventricular ejection fraction (LVEF). Higher titers of circulating IL-4 and IL-10 were observed at D30 versus D1 (P=0.013 and P<0.001, respectively). Titers of IL-6 at D1 were associated with infarcted mass (rho = 0.41, P<0.001) and inversely related to LVEF (rho = -0.38, P<0.001). After multiple linear regression analysis, high-sensitivity troponin T and IL-6 collected at day 1 were independent predictors of infarcted mass and, at day 30, only HDL-C. Regarding LVEF, high-sensitivity troponin T and high-sensitivity C-reactive protein were independent predictors at day 1, and B2 classic lymphocytes, at day 30. In subjects with STEMI, despite early reperfusion, the amount of infarcted mass and ventricular performance were related to inflammatory responses triggered by circulating B lymphocytes