Clays, soils and alterations
The research team focuses on petrography and mineralogy of the clay materials. Its researches include a large field: from the rock to the internal structure of the mineral.
- The study of crystal-textures and properties of clays in complex media such as rocks and soils is a good way to reconstitute the physico-chemical mechanisms that have controlled their evolution over time.
Many projects are planned within the framework of several national programs (ORE Prairie FORPRO GDR-Trias, GDR CNRS-3 SAFETY IRSN) and international programs (POSINAM http://www.posinam.eu/).
- One of the ASA missions is to open its scientific, analytical and educational competence to the national community and to foreign students and researchers through a efficient analysis service to characterize clay materials, rocks and clays minerals; and most importantly, to provide a scientific expertise in the field of petrography and crystal chemistry of clay applied to soils and weathered rocks – diagenesis and hydrothermal alteration on the one hand, and on the other hand in the field of infrared spectroscopy and syntheses mineral. A draft “National Master ‘Clay’”, which started in 2009, supported by the French Group of Clays, strengthens this mission. This is to gather in the same place nationally selected students with a multi-and trans-disciplinary program (Physics – Chemistry – Biology – Earth Science) taught by the best specialists. This program is now complemented by the Erasmus Master Mundus IMACS which has an international dimension and is selected by the European Commission.
ASA has 2 innovative research projects.
- The first project is the change of scale. The structure of clays and clay minerals is a very complex one. The structure is difficult to study because of the very small size of the clay particles and because of their “flexibility”. In recent years, the focus has been on the characterization of these textures by microtomography. Thus, notable progress was made Clear improvements were also achieved in the field of hydration effect on porosity, which opens up the perspective of linking the observed phenomena from the crystal size (micron) to the millimetric aggregate. The challenge is to extend this change of scale to the dcm, this scaling up dcm (European Programmes FUNMIG, NFPRO).
- The purpose of the second project is to determine the interrelationships between the crystal-chemical, physicochemical, thermodynamic and spectroscopic properties. This project is based on synthesis of clays which makes it possible to obtain minerals with controlled crystal-chemical and textural properties (Programmes LTD, Thermochemistry, CPER axis Eco Industries). Thus begins a theory on the synthesis of iron- controlled clays. The goal is to obtain clays with iron-controlled status (structural iron content, distribution Fe2 + / Fe3 +) and to establish relations iron status – conditions of formation (pH, Eh, T, …).
- Given that ferriferous clays are considerably involved in electron transfer, applications are envisaged in water treatment (degradation of organic molecules) and management of hydromorphic soils. In addition, a local collaboration has been implemented with LACCO (UMR6503) for the development of synthetic clays that can be used in catalysis. The idea is to synthesize clays with active elements in their structure.
- The researches conducted have been focusing on the transfer of water and solutes in heterogeneous fractured reservoirs. The questions studied have implications vis-à-vis the two major environmental issues: the management of groundwater resources and underground storage of waste.
- The scientific approach is based on a approach linking measurements / experiments / modeling. In recent years, research has been closely tied to the Hydrogeological Experimental Site (SEH-> 207) of Poitiers, developed in the framework of the “WATER” Program of the CPER 2002-2007.
In addition to the observation task linked to the Observation Service H +, the research project conducted by the group “Hydr” have the purpose to develop new approaches in the characterization and modeling of fractured carbonate aquifers. This approach is both theoretic-digital and experimental.
Four points to present the scientific project:
Research Project 1 : Benchmark hydrodynamic SEH: MACH-1 Project.
The project EC2CO/MACH-1 (Modeling of Heterogeneous Carbonate Aquifers – 1. Flow dynamics), supported by INSU since 2006, has the purpose of establishing a benchmark hydrogeological HEU from several conceptual and numerical modeling approaches. Eight research teams are involved in this project: the Laboratory Sciences of Climate and Environment (LSCE UMR 1572), the Institute of Fluid Mechanics of Strasbourg (UMR 7507 IMFS) Hydrasa (UMR 6532), Geosciences Rennes (UMR 6118 ), the Centre for Geosciences, the Ecole Nationale Supérieure des Mines de Paris (CG-ENSMP UMR 7619), the Department of Physics and Detonics (LCD UPR 9028) Sisyphus (UMR 7619), HydroSciences Montpellier (HSM UMR 5569). The modeling scale that has been considered is a limestone block of 200 mx 200 mx 100 m, which corresponds with an area where the data density is particularly high HEU (25 holes positioned in a regular geometric arrangement of “five-spot”/multi-scale symmetry type).
The modeling exercise predicts the response of the layer (calculation of the drawdowns at several piezometers level) for two pump tests to be carried out afterwards. The goal of the MACH-1 project is to analyze the relevance of different models (several digital/conceptual approaches) in their way to understand the multi-scale heterogeneity of the environment, or at least in their way to integrate the effects induced by these heterogeneities on the flow dynamics.
Research Project 2: Scale-up and opposite problem.
This project intends to conciliate (1) the multi-scale characteristic of heterogeneities in carbonate aquifers, (2) the high variability of the characteristic scales of measurements corresponding to the current methods of and hydraulic and geophysical investigations and (3) the minimum size of the mesh in reservoir models operating on a large scale. This research project is a continuation of the work done in collaboration with other teams through the GDR CNRS 2990 “HTHS” (Hydrodynamics and Transfers in Underground Hydrosystems). All hydraulic data and transport data collected on the SEH should be critically reinterpreted in the framework of a “Scale-up” and “Opposite problem”, by making use of the regular and symmetrical arrangement of the HEU drillings (multi-scale “five-spot” device).
Research Project 3: Dynamics of the transport of dissolved chemical species
The information gained on the structure of flows (geophysical investigations conducted over the 2002-2006 period) make scientists able to study the dynamics of the transport of solutes. This task involves a dual problem of characterization and modeling. The research project would focus on two points:
- Development of new chemical tracers adapted to the problem of multi-tracing and reinjection in a doublet pumping configuration. This operation will be implemented in cooperation with the Laboratory of Chemistry of Water and Environment (CEAA UMR 6008) and the Laboratory of Synthesis and Reactivity of Natural Substances (SRSN UMR 6514). It should be underlined that scientific relations have already existed for years between HydrASA and these two chemistry laboratories.
- Interactions water/ rock and hydrogeochemistry of tanks: explaining the origin and the hydrogeochemical dynamic of dynamics of selenium in the groundwater “Dogger”, which is a problem at the regional level. The researchers would focus in particular on the research of indicators to (1) identify the mineral origin of Selenium in the “Dogger” aquifer and (2) to distinguish between the transitory effects of high frequency (high speed in preferential flow paths) and the low frequency circulation “of water”;
Research Project 4: Development of innovative techniques (pilot) biochemical in situ decontamination of groundwater.
The laboratory Hydrasa and the Chemistry of Water and Environment (CEAA UMR 6008) are currently developing together an in-situ biochemical pilot of decontamination of groundwater vis-à-vis nitrates (Marion Chatelier ‘s Thesis). The Poitou-Charentes region supports this objective (the “Eaux-Sols” CPER 2007-2013). Two types of experiments are going to be conducted to study the design and efficiency of the pilot:
- Laboratory experiments to study the kinetics of the biochemical processes;
- Experiences at the field scale: plots associated with pumping tests “in doublet”, to characterize the flows of dilution and the hydrodispersion of the contaminant in the reactor.
These experimentation will be complemented by the development of a numerical model that will examine the feasibility and optimization of the pilot. This modeling phase will rely on the work done in axis 1 (MACH-1 projects), axis 2 (inverse modeling) and axis 3 (characterization of transport processes).