Christophe Fond

Two-dimensional THM modelling of the large scale natural hydrothermal circulation at Soultz-sous-Forêts

BackgroundA two-dimensional numerical model is developed for the Soultz-sous-Forêts reservoir from an idealized cross-section containing six homogeneous horizontal layers. The considered constitutive equations are those of homogenized saturated porous media involving Thermo-Hydro-Mechanical (THM) couplings, and most of materials properties (for brine and rocks) are taken dependent on temperature and pressure.MethodsThe constitutive equations are solved in transient regime with the finite element software Code_Aster to reach a stationary state of the reservoir.ResultsWe show that a large scale natural convection is compatible with present boundary conditions if the permeability of the reservoir is of the order of 1.0×10−14m2. Convection cells are of the order of 1.3 km in width and we analyze several vertical profiles and maps of physical properties.ConclusionsA stationary convective solution at large scale is highlighted.

Longitudinal dynamic fracture of polymer pipes

To study the rapid crack propagation (RCP) resistance of polymer pipes, an experimental set-up and a numerical model are proposed. The way to solicit polymer pipes, imposed displacements or pressure, is discussed. Indeed, it has been demonstrated that it is necessary to load polymer pipe with imposed displacements and not internal gas pressure. For a pressurised pipe, a relevant estimation of the energy released rate is difficult because of the work of external forces which can not be precisely determined during crack propagation and of course during gas leak. An experimental set-up, with imposed displacements, has been machined to ensure an approximately L = 13R permanent RCP regime with L and R which are, respectively, the length and the radius of the pipe. The energy release rate is then calculated with the help of a finite element procedure knowing the crack tip location.

Multi-scale roughness measurement of cementitious materials using different optical profilers and window resizing analysis

In the development of new eco-cements for ecologically friendly construction, the porosity, surface structure and chemical nature of the material can influence the bioreceptivity of the surface and the aptitude or not of environmental micro-organisms to form biofilms. Such films are the source of biocontamination that can lead to a degradation in the structural properties over time. Accurate measurement of surface roughness and topography are important to help in the understanding of this interaction. Optical profilers are well adapted to the quantifying of large surface roughness typical of cementitious materials, being more rapid and better able to cope with high roughness compared with stylus and near field probe techniques. But any given surface profiler typically has specific range limits in terms of axial and lateral resolution and field of view, resulting in different roughness values according to the type of optical profiler used. In the present work, unpolished and polished cement paste samples have been measured with two different systems, one using interference microscopy and the other, chromatic confocal sensing. Comparison of the results from both techniques using the method of window re-sizing, more commonly used in tribology, has been used for calculating the average roughness parameters at different scales. The initial results obtained show a successful overlap of the results for the unpolished samples and a slight separation for the polished samples. The validation of the measurements is demonstrated together with a revealing of differences in the measurements on different types of surfaces due to variations in instrument performance.

Failure Process of Recycled Concrete Aggregate Mortars Based on Digital Image Correlation

This study addresses the failure process of mortars made of three different sands. Prismatic 40 × 40 × 160 mm3 specimens were tested less than three points bending after 28 days of curing. Compressive tests were conducted on the two fragments of each mortar resulted from above flexural tests. The three different materials were: standard mortars performed with 0/2 mm natural rolled sand, mortars performed with 0/2 mm crushed sand and mortars performed with 0/2 mm fine recycled concrete aggregate (FRCA).The main aim of this experimental campaign was to study the influence on the mechanical properties of the substitution of natural sand (standardized or crushed gravel) with recycled sand when granular skeletons are identical. Crack propagation, displacement and strain fields, mechanical properties and other model parameters were obtained using 2D-DIC.The findings in these investigations could also be useful to understand the failure process and to improve the mechanical properties of mortars performed of FRCA by optimizing the granular skeleton.