Time filter

Source Type

Madeo A.,CNRS Laboratory of Civil and Environmental Engineering | Madeo A.,International Research Center M and MoCS | Djeran-Maigre I.,CNRS Laboratory of Civil and Environmental Engineering | Djeran-Maigre I.,International Research Center M and MoCS | And 3 more authors.
Continuum Mechanics and Thermodynamics | Year: 2013

In geomechanics, a relevant role is played by coupling phenomena between compressible fluid seepage flow and deformation of the solid matrix. The behavior of complex porous materials can be greatly influenced by such coupling phenomena. A satisfactorily theoretical framework for their description is not yet completely attained. In this paper, we discuss how the model developed in dell'Isola et al. (Int J Solids Struct 46:3150-3164, 2009) can describe how underground flows or, more generally, confined streams of fluid in deformable porous matrices affect compression wave propagation and their reflection and transmission at a solid-material discontinuity surface. Further work will investigate the effect of stream flow in porous media on shear waves, generalizing what done in Djeran Maigre and Kuznetsov (Comptes Rendus Mécanique 336(1-2):102-107, 2008) for shear waves in one-constituent orthotropic two-layered plates. The presented treatment shows that the presence of fluid streams considerably affect reflection and transmission phenomena in porous media. © 2012 Springer-Verlag.

Brun M.,CNRS Laboratory of Civil and Environmental Engineering | Batti A.,CNRS Contacts and Structural Mechanics Laboratory | Combescure A.,CNRS Contacts and Structural Mechanics Laboratory | Gravouil A.,CNRS Contacts and Structural Mechanics Laboratory | Gravouil A.,Institut Universitaire de France
Finite Elements in Analysis and Design | Year: 2014

External coupling software based on the coupling algorithm proposed by Prakash and Hjelmstad (PH method) is compared to the previous external coupling software based on the GC (Gravouil and Combsecure) method. The salient features of multi-time-step partitioning methods are presented: they involve non-overlapping partitions and follow a dual Schur approach by enforcing the velocity continuity at the interface with Lagrange multipliers. The main difference between the two methods lies in the time scale at which the interface problem is solved: the micro-time scale for the GC algorithm and macro-time scale for the PH algorithm. During the multi-time-step co-computations involving two finite element codes (explicit and implicit FE codes), the tasks carried out by the coupling software PH-CPL, based on a variant of the PH algorithm, are illustrated and compared to the coupling software GC-CPL based on the GC algorithm. The advantage of the new coupling PH-CPL software is highlighted in terms of parallel capabilities. In addition, the PH-CPL coupling software alleviates the dissipative drawback of the GC method at the interface between the subdomains. Academic cases are investigated to check the energy features and the accuracy order for the GC and PH algorithms. Finally, explicit/implicit multi-time-step co-computations with GC-CPL and PH-CPL software are conducted for two engineering applications under the assumption of linear elastic materials: a reinforced concrete frame structure under blast loading striking its front face and a flat composite stiffened panel subjected to localised loads applied to its central frame. © 2014 Elsevier B.V. All rights reserved.

Gravouil A.,Institut Universitaire de France | Combescure A.,CNRS Contacts and Structural Mechanics Laboratory | Brun M.,CNRS Laboratory of Civil and Environmental Engineering
International Journal for Numerical Methods in Engineering | Year: 2014

SUMMARY: Computational structural dynamics plays an essential role in the simulation of linear and nonlinear systems. Indeed, the characteristics of the time integration procedure have a critical impact on the feasibility of the calculation. In order to go beyond the classical approach (a unique time integrator and a unique timescale), the pioneer approach of Belytschko and co-workers consisted in developing mixed implicit-explicit time integrators for structural dynamics. In a first step, the implementation and stability analyses of partitioned integrators with one time step have been achieved for a large class of time integrators. In a second step, the implementation and stability analyses of partitioned integrators with different time steps were studied in detail for particular cases. However, stability results involving different time steps and different time integrators in different parts of the mesh is still an open question in the general case for structural dynamics. The aim of this paper is to propose a state-of-the art of heterogeneous (different time schemes) asynchronous (different time steps) time integrators (HATI) for computational structural dynamics. Finally, an alternative approach based on energy considerations (with velocity continuity at the interface) is proposed in order to develop a general class of HATI for structural dynamics. © 2014 John Wiley & Sons, Ltd.

Xu H.,Hong Kong Polytechnic University | Su Z.,Hong Kong Polytechnic University | Cheng L.,Hong Kong Polytechnic University | Guyader J.-L.,INSA Lyon | Hamelin P.,CNRS Laboratory of Civil and Environmental Engineering
Structural Health Monitoring | Year: 2013

Interfacial debonding in multilayered engineering structures can jeopardize the structural integrity without timely awareness. By reconstructing the distribution of interfacial forces and canvassing local perturbance to the structural dynamic equilibrium, an identification approach for interfacial debonding between different structural components was developed. A "debonding index," governed by the derivatives of reconstructed interfacial forces, was established, able to predict debonding in a quantitative manner including the coexistence of multi-debonding and their individual locations and sizes. The index offers the flexibility of detecting debonding between a beam-like component and its neighboring constituents of any type (beam, plate, shell, or even more complex components) with distinct material properties. To enhance the robustness of the approach under noisy measurement conditions, two denoising techniques (low-pass wavenumber filtering and adjustment of measurement density), together with a data fusion algorithm, were proposed. Using a noncontact laser vibrometry, the approach was validated experimentally by identifying multiple debonding zones in a steel-reinforced concrete slab dismantled from a bridge model. The approach has been demonstrated sensitive to debonding of small dimension owing to the use of high-order differential equation of motion. In addition, it does not require a global model of the entire system, prior information on structural boundaries, benchmark, baseline signals, and additional excitation sources as long as the structure undergoes steady vibration. © The Author(s) 2013.

Arias L.,IRSTEA | Bertrand-Krajewski J.-L.,CNRS Laboratory of Civil and Environmental Engineering | Molle P.,IRSTEA
Water Science and Technology | Year: 2014

Designing vertical-flow constructed wetlands (VFCWs) to treat both rain events and dry weather flow is a complex task due to the stochastic nature of rain events. Dynamic models can help to improve design, but they usually prove difficult to handle for designers. This study focuses on the development of a simplified hydraulic model of French VFCWs using an empirical infiltration coefficient - infiltration capacity parameter (ICP). The model was fitted using 60-second-step data collected on two experimental French VFCW systems and compared with Hydrus 1D software. The model revealed a season-by-season evolution of the ICP that could be explained by the mechanical role of reeds. This simplified model makes it possible to define time-course shifts in ponding time and outlet flows. As ponding time hinders oxygen renewal, thus impacting nitrification and organic matter degradation, ponding time limits can be used to fix a reliable design when treating both dry and rain events. © IWA Publishing 2014.

Chen M.,CNRS Laboratory of Civil and Environmental Engineering | Blanc D.,CNRS Laboratory of Civil and Environmental Engineering | Gautier M.,CNRS Laboratory of Civil and Environmental Engineering | Mehu J.,CNRS Laboratory of Civil and Environmental Engineering | Gourdon R.,CNRS Laboratory of Civil and Environmental Engineering
Waste Management | Year: 2013

Ashes produced by thermal treatments of sewage sludge exhibit common properties with cement. For example, major elements present in SSA are the same of major elements of cement. Hydraulic properties of SSA are quite the same of cement ones. They may therefore be used to substitute part of cement in concrete or other cementitious materials, provided that technical prescriptions are satisfied and that environmental risks are not significantly increased.The objective of the present study was to determine the appropriate substitution ratios to satisfy both technical and environmental criteria. In a first step, the elemental composition and particle size distribution of the ashes were measured. Then the ashes were used along with Portland cement and sand at different ratios of substitution to produce mortar and concrete which were cured for up to 90. days into parallelepipedic or cylindrical monoliths. The mechanical properties of the monoliths were measured using standard procedures for flexural and compressive strengths, and compared to blanks containing no ashes. The environmental criteria were assessed using leaching tests conducted according to standard protocols both on the ashes and the monoliths, and compared to the blanks.Results showed that the characteristics of the ashes ranged between those of cement and sand because of their larger particle size and higher content in SiO2 as compared to cement. The monoliths made with the highest substitution ratios exhibited a significant decrease in flexural and compressive strengths. However, when the ashes were used in partial substitution of cement at appropriate ratios, the concrete monoliths exhibited similar compressive strengths as the blank samples. The most appropriate ratios were found to be 10% substitution of cement and 2% substitution of sand.The leaching tests conducted on the ashes in their powdery form revealed that amongst the potential contaminants analyzed only Mo and Se were leached at concentrations above the threshold limits considered. The leaching tests conducted on concrete monoliths showed however that none of the contaminants monitored, including Mo and Se, were leached above the limits. In addition, whether concrete recipe incorporated ashes or not, similar concentrations were measured for each potential contaminant in the leachates. This result indicated that mixing ash with cement and sand to produce mortar or concrete induced a stabilization of Mo and Se and thereby constituted in itself a good treatment of the ashes. © 2013 Elsevier Ltd.

Kuryatnyk T.,CNRS Laboratory of Civil and Environmental Engineering | Chabannet M.,CNRS Laboratory of Civil and Environmental Engineering | Ambroise J.,CNRS Laboratory of Civil and Environmental Engineering | Pera J.,CNRS Laboratory of Civil and Environmental Engineering
Cement and Concrete Research | Year: 2010

The water resistance of plaster of Paris is limited due to the high solubility of calcium sulphate hemihydrate. In order to improve this resistance, calcium sulphoaluminate clinker was added to plaster at different contents: 30, 50, and 70%. Mortars were cast using these new binders and subjected to the Soxhlet extraction test. The presence of calcium sulphoaluminate clinker considerably reduced the quantity of sulphate extracted per day and after 5 days: from 78.9% to 89.1%. The analysis of microstructure showed the stability of ettringite during the leaching test and the refinement of the porosity. © 2010 Elsevier Ltd. All rights reserved.

Plante B.,University of Québec | Bussiere B.,University of Québec | Benzaazoua M.,University of Québec | Benzaazoua M.,CNRS Laboratory of Civil and Environmental Engineering
Journal of Geochemical Exploration | Year: 2012

It is crucial for mining operators to predict the acid-generating potential of their mine wastes as early as possible in a mine development project, because of the high remediation costs of acid-generating tailings and the risks of environmental issues associated with an incorrect classification of the wastes. However, many tailings having low net acid-generating potentials fall into the uncertainty zone of the static test. Different chemical and mineralogical static test results are compared in this paper for 5 Canadian hard rock mine tailings having low net acid-generating potential, in order to help determine which method is more appropriate for such tailings. Static test methods showed significant result variations (NNP or NP/AP) for each tailings tested, demonstrating the need to develop tools to identify the most appropriate technique for a given mine waste. Thus, static test selection guidelines were developed based on mineralogical considerations for each test. A modification to the Lawrence and Scheske method based on the Paktunc CNP method is proposed in order to improve its accuracy, which enables to account for the presence of oxidizable cations (such as iron and manganese) within the minerals. © 2011 Elsevier B.V.

Couvidat J.,CNRS Laboratory of Civil and Environmental Engineering | Benzaazoua M.,CNRS Laboratory of Civil and Environmental Engineering | Chatain V.,CNRS Laboratory of Civil and Environmental Engineering | Zhang F.,CNRS Laboratory of Civil and Environmental Engineering | Bouzahzah H.,CNRS Laboratory of Civil and Environmental Engineering
Environmental science and pollution research international | Year: 2015

Contaminated dredged sediments are often considered hazardous wastes, so they have to be adequately managed to avoid leaching of pollutants. The mobility of inorganic contaminants is a major concern. Metal sulfides (mainly framboïdal pyrite, copper, and zinc sulfides) have been investigated in this study as an important reactive metal-bearing phase sensitive to atmospheric oxygen action. An oxygen consumption test (OC-Test) has been adapted to assess the reactivity of dredged sediments when exposed to atmospheric oxygen. An experimental column set-up has been developed allowing the coupling between leaching and oxygen consumption test to investigate the reactivity of the sediment. This reactivity, which consisted of sulfide oxidation, was found to occur for saturation degree between 60 and 90 % and until the 20th testing week, through significant sulfates releases. These latter were assumed to come from sulfide oxidation in the first step of the test, then probably from gypsum dissolution. Confrontation results of OC-Test and leachate quality shows that Cu was well correlated to sulfates releases, which in turn, leads to Ca and Mg dissolution (buffer effect). Cu, and mostly Zn, was associated to organic matter, phyllosilicates, and other minerals through organo-clay complexes. This research confirmed that the OC-Test, originally developed for mine tailings, could be a useful tool in the dredged sediment field which can allow for intrinsic characterization of reactivity of a material suspected to readily reacting with oxygen and for better understanding of geochemical processes that affect pollutants behavior, conversion, and transfer in the environment.

Metadier M.,Safege | Metadier M.,CNRS Laboratory of Civil and Environmental Engineering | Bertrand-Krajewski J.L.,CNRS Laboratory of Civil and Environmental Engineering
Water Science and Technology | Year: 2011

Continuous high resolution long term turbidity measurements along with continuous discharge measurements are now recognised as an appropriate technique for the estimation of in sewer total suspended solids (TSS) and Chemical Oxygen Demand (COD) loads during storm events. In the combined system of the Ecully urban catchment (Lyon, France), this technique is implemented since 2003, with more than 200 storm events monitored. This paper presents a method for the estimation of the dry weather (DW) contribution to measured total TSS and COD event loads with special attention devoted to uncertainties assessment. The method accounts for the dynamics of both discharge and turbidity time series at two minutes time step. The study is based on 180 DW days monitored in 2007-2008. Three distinct classes of DW days were evidenced. Variability analysis and quantification showed that no seasonal effect and no trend over the year were detectable. The law of propagation of uncertainties is applicable for uncertainties estimation. The method has then been applied to all measured storm events. This study confirms the interest of long term continuous discharge and turbidity time series in sewer systems, especially in the perspective of wet weather quality modelling. © IWA Publishing 2011.

Loading CNRS Laboratory of Civil and Environmental Engineering collaborators
Loading CNRS Laboratory of Civil and Environmental Engineering collaborators