Modelling of metal polluant leaching through a smectite.

International audienceLaboratory tests are performed to characterise the soaking and retention properties of a clay barrier (Fo-Ca) under controlled homogeneous conditions. A physical model that allows calculating the retention properties and kinetics observed during the test is then detailed, and lastly simulations are examined using various soaking conditions. The results show the model predictions of cumulative cation concentrations in leachates (i.e. copper retention by clay). These curves are accurately fit by the model with the experimental data for the leaching phenomena. Clay retention capacity until reaching a physical limit in the exchanges is evidenced as well, with this limit being input into the model as the clay CEC

Assessment of the performance of asphalt rubber layers on noise abatement

Layers with a very high content of rubber have shown to be very effective on noise abatement despite their reduced durability. On the contrary, layers with a rubberized asphalt binder have shown to be durable, but their performance regarding noise abatement is not consensual yet. This paper aims at assessing the effect of the use of layers with rubberized asphalt binder on noise abatement. For this purpose seven road sections with different surface types, among which five gap graded and three with rubberized asphalt have been selected. In these road sections the tyre-road noise generated by a heavy truck and two light vehicles at three levels of speed were measured by means of pass-by tests. Surface texture tests were also performed. The results focused on the noise level variation versus speed, the average noise level for each speed level versus type of surface and the average noise level variation with regards to a reference surface. Mixtures with rubberized asphalt did not show a significantly better performance. In fact, the same performance may be achieved with other type of gap graded thin mixtures. The results obtained might be better explained if other parameters than the rubberized asphalt binder are taken into account. Further research on the effect of porosity and texture on noise generation is being done. It is intended to perform absorption tests in all the surfaces analysed in order to study this issue in depth and fully understand the effect of the rubber on noise generation

Simulation of pollutant transport investigated through an expansive clay.

In the framework of domestic waste disposals, the in-situ compaction of soil is usually used to obtain engineered clay barriers with suitable confining properties. Permeability and pollutant retention are the major properties which should be investigated in this context for barrier evaluation. Considering clay barriers in contact with waste leachates, they may be saturated by solutes of various chemical compositions, including in particular toxic heavy metals. In this context, the expansive Fo-Ca clay, a natural Ca-smectite from the Paris basin of Ypersian (Sparnacian) age, was chosen because of its very low permeability and ability for pollutant retention through cationic exchanges. The smectic is associated with kaolinite (up to 20%), and minor quartz, calcite, goethite and gypsum

Numerical evaluation of tyre/road contact pressures using a multi-asperity approach

International audienceThe interaction between the tyre and the road surface is responsible for many physical problems such as skid resistance, rolling resistance or noise generation. This paper deals with the numerical study of tyre/road contact. A two-scale iterative method is used for solving the contact problem between a multi-asperity road surface and an elastic half-space. This method has been used successfully for idealized rough surfaces. However, for efficient applications to real surfaces, an appropriate partition of the surfaces is required. A partitioning method is proposed to describe road surfaces using classical image processing and a new load/penetration relation for a single road asperity is introduced. In order to evaluate the efficiency of the method, numerical results for a small sample of road are compared to a classical matrix inversion method, which show at macro-scale a rather good accuracy to predict tyre/road noise. At micro-scale both methods give the same results, but the multi-asperity method is much less time-consuming. Then numerical evaluation of tyre/road static contact pressures for different road textures at full contact area is presented. This approach with new preconditioning can be a reliable and efficient method to simulate contact problems with large surfaces

A new algorithm for computing the indentation of a rigid body of arbitrary shape on a viscoelastic half-space

In this paper the contact problem between a rigid indenter of arbitrary shape and a viscoelastic half-space is considered. Under the action of a normal force the penetration of the indenter and the distribution of contact pressure change. We wish to find the relations which link the pressure distribution, the resultant force on the indenter and the penetration on the assumption that the surfaces are frictionless. For indenters of arbitrary shape the problem may be solved numerically by using the Matrix Inversion Method (MIM), extended to viscoelastic case. In this method the boundary conditions are satisfied exactly at specified "matching points" (the mid-points of the boundary elements). It can be validated by comparing the numerical results to the analytic solutions in cases of a spherical asperity (loading and unloading) and a conical asperity (loading only)

Movements and space use of giant trevally in coral reef habitats and the importance of environmental drivers

Background: Effective conservation of large predators requires a broad understanding of their ecology. Caranx ignobilis is a large marine predator well represented in coral reef environments, yet they are poorly studied. Passive acoustic monitoring was used to track the movements of 20 C. ignobilis at offshore reefs in the central Great Barrier Reef from 2012 to 2014. Using a modelling approach, temporal changes in movement patterns of C. ignobilis were explored to determine if individuals exhibited predictable movement patterns. The effects of biological and environmental variables on monthly space use, daily presence and hourly depth use were investigated to define any response to environmental changes. Results: Caranx ignobilis typically remained at their capture reef with 98.8% of detections recorded at these locations. Individuals were recorded in the study site for periods from 9 to 335 days (mean = 125.9) with a mean residency index of 0.53, indicating movements away from the reef or out of detection range occurred on the scale of days. Inter-reef movements from only three individuals were recorded which coincided with the summer full moon so may have been related to spawning behaviour. Environmental drivers were correlated with daily presence and hourly depth use of C. ignobilis but had little influence on monthly space use. There was little or no effect of fish size on space use, presence and depth use. Conclusion: By improving the current understanding of movement patterns of this large teleost among individual coral reefs, the results of this study reveal that site attachment may be present and that environmental parameters play a role in observed movement patterns related to depth and presence. These data provide useful information for the development of management plans, particularly in relation to space-based protection

Silent surfaces : an experience in Portugal

It is acknowledged that traffic noise affects human behaviour and health. Measures aiming at mitigating the impact of traffic noise are not always viable in urban areas. In Portugal, road designers have recently started to consider silent surfaces as alternative within their road pavement projects. In this paper the tire-surface noise of three surface layers integrated in a rehabilitation project carried out in an urban road that carries more than 40000 vehicles per day is assessed: i) one dense asphalt layer with limited maximum aggregate size, following the SILVIA recommendations for low noise surfaces; ii) two very-thin surfaces with different grading, which are an adaptation of the very-thin layers widely used in France to Portuguese conditions. The surface layers were constructed consecutively, involving segment lengths with more than 500 m. The surface texture was measured using a high speed profilometer. Skid resistance was also measured. The noise level was measured both by pass-by tests with selected traffic (trucks and light vehicles) at several speeds and by close proximity tests. The thin layers tested provided very good noise reduction values, especially at high speeds, and had a better performance than gap graded asphalt rubber surfaces frequently used in Portugal

Improved VSF Algorithm for Smooth Surface Reconstruction from Sparse Medical Data

This paper presents a Modified Variational Splines Fitting (MVSF) algorithm for surface reconstruction using thin plate splines on scattered patches or points of originally smooth surfaces. In particular, a more accurate derivation of the discrete equations for the energy corresponding to the thin plate model is introduced. The results obtained on simulated data show that the proposed algorithm converges faster than the original VSF algorithm. Additionally, we discuss an approach for choosing the algorithm’s parameters using a cross validation technique. Results obtained with the modified algorithm are compared to those using a Frequency Fourier-based 3D Harmonic modelling (3DHM) algorithm and show that the proposed algorithm gives an improved performance under the small sample size condition. The developed model has been successfully applied for real biomedical data; in particular for the reconstruction of left ventricle of human heart

Chan-Vese based method to segment mouse brain MRI images: application to cerebral malformation analysis in trisomy 21

International audienceIn this paper, a semi automatic active contour method based on Chan-Vese model is proposed for the segmentation of mouse brain MR images. First, a 2 ½ D strategy is applied on the axial images to segment the 3D volume of interest. The method takes into account the special shape of the object to segment. Moreover, the user defines the limits where to search these contours and also provides an initial contour. This semi automatic method makes that human intervention is limited and the tedious manual handling is greatly reduced. Results have shown that the brain volumes estimated by the method are identical to expert manually estimated volumes. Last but not least, the new method was used in the analysis of the cerebral malformations linked to Trisomy 21: no significant difference of the brain volumes between Tri-somy 21 mice and the control ones were found