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Sedimentology and Geochemical Evaluation of Lignite-argillite Sequences in a Named Basin in Bali Nyonga, Northwest, Cameroon

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International Journal of Geosciences 2015年第8期6卷 917-937页

作者： Roger Ngong Ngia Christopher M. Agyingi Josepha Foba-Tado Germain M. M. Mboudou Anita Nshukwi Victorine N. Beckley Department of Geology University of Buea Buea Cameroon Department of Chemistry University of Buea Buea Cameroon

The sedimentology and geochemistry (major and trace element compositions) of lignite and argillite (carbonaceous shale and claystone) sequences in a Basin in Bali Nyonga, west of the Bamenda Mountain have been investigated to determine their sequences and the prevailing environmental?conditions which control their formation. Ten representative samples were obtained fromtrenches, pits, and river and stream valleys in the study area. These samples and their ashes were subsequently examined using X-ray fluorescence spectrometry (XRF), inductively coupled plasma spectrometry (ICP), and X-ray diffraction analysis (XRD). The geochemical results revealed that thelithophile, chalcophile and siderophile elements were dominantly epigenetic in origin, mainly?from detrital sources supported by high silica and alumina concentrations in all the samples. The mineral phases identified were quartz, kaolinite, illite, pyrite, hematite, and minor phases of feldspars,pseudorutile. The relatively high silica (54.10 wt%) and alumina contents (27.77 wt%) in these?samples can be explained by high detrital input during peat formation. The low contents of MgO and CaO in the analysed samples agree very much with the continental setting of the peat formating basin. A clayey microband derived from alkaline volcanic ashes was identified in the lignite and the dominant composition of these clayey microbands was mixed-layer clay minerals of illite and kaolinte, which were interlayered with organic bands. The modes of occurrence of ash bands indicated that the volcanic activities were characterized by multiple eruptions, short time interval?and small scale for each eruption during peat accumulation. The ratios of redox-sensitive traceelement (V/Cr versus Ni/Co and V/V + Ni versus Ni/Co), Sr/Ba, and major oxides ratio (CaO + MgO + Fe2O3)/(SiO2?+ Al2O3) from the analysed samples from Bali Nyonga indicate a terrestrial, reductive (oxic), littoral to brackish water environmental conditions which are ch

关键词： Lignite Bali Nyonga argillite Clay Minerals Cameroon Volcanic Line (CVL) Lacustrine Basin

Approaches for representing hydro-mechanical coupling between sub-surface excavations and argillaceous porous media at the ventilation experiment, Mont Terri

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Journal of Rock Mechanics and Geotechnical Engineering 2013年第2期5卷 85-96页

作者： Alexander Bond Alain Millard Shigeo Nakama Chengyuan Zhang Benoit Garritte Quintessa Ltd. Chadwick House Birchwood Park Warrington Cheshire A3 6AEUK Commissariatà l'Energie Atomique YvetteFrance Japan Atomic Energy Agency (JAEA) Tokai Japan Institute of Rock and Soil Mechanics Chinese Academy of Sciences Universidad Politcnica de Catalunya Barcelona Spain

At the Mont Terri Underground Research Laboratory （Switzerland）, a field-scale investigation has been conducted in order to investigate the hydro-mechanical and chemical perturbations induced in the argilla- ceous formation by forced ventilation through a tunnel. This experiment has been selected to be used for processing model development and validation in the international project DECOVALEX-2011. The con- ceptual and mathematical representation of the engineered void, which itself forms a major part of the experiment and is not simply a boundary condition, is the subject of this paper. A variety of approaches have been examined by the contributors to DECOVALEX and a summary of their findings is presented here. Two major aspects are discussed. Firstly, the approaches for the treatment of the surface condition at the porous media/tunnel interface are examined, with two equivalent but differing formulations successfully demonstrated. Secondly, approaches for representing the tunnel with associated air and water vapour movement, when coupled with the hydro-mechanical （HM） representation of the porous medium, are also examined. It is clearly demonstrated that, for the experimental conditions of the ventilation experiment （VE） that abstracted physical and empirical models of the tunnel, can be used successfully to represent the hydraulic behaviour of the tunnel and the hydraulic interaction between the tunnel and the surrounding rock mass.

关键词： Tunnel Water vapour Hydro-mechanical (HM) coupling Numerical modelling Mont Terri Underground Research Laboratory (URL) Ventilation experiment (VE) argillite

Accounting for anisotropic effects in the prediction of the hydro-mechanical response of a ventilated tunnel in an argillaceous rock

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Journal of Rock Mechanics and Geotechnical Engineering 2013年第2期5卷 97-109页

作者： Alain Millard Alex Bond Shigeo Nakama Chengyuan Zhang Jean-Dominique Barnichon Benoit Garitte Commissariatà l'Energie Atomique et aux Energies Alternatives Gif-sur-Yvette France Quintessa Ltd. Chadwick House Birchwood Park Warrington Cheshire WA3 6AE UK Japan Atomic Energy Agency Tokai Japan Insititute of Rock and Soil Mechanics Chinese Academy of Sciences Institute for Nuclear Radioprotection and Safety Fontenay-aux-roses France Universidad Politécnica de Catalunya Barcelona Spain

In order to investigate the hydro-mechanical （HM） and chemical perturbations induced in an argillaceous formation by forced ventilation during the operational period of a nuclear waste repository, a specific experiment has been performed in a tunnel, at Mont Terri Underground Research Laboratory （URL） in Switzerland. This experiment has been selected in the international project DECOVALEX for model vali- dation and the numerical simulation of this ventilation experiment （VE） is the object of the present paper. Since the argillaceous rock exhibits anisotropic properties, particular attention is given to the evaluation of the effects of various anisotropic features on the predicted results. In situ measurements such as relative humidity （RH）, global water mass extracted, pore water pressure, water content, and relative displace- ments are compared to predictions using both isotropic and anisotropic parameters. Water permeability anisotropy is shown to be the most influencing parameter by far, whereas in situ stress anisotropy has an effect only during the excavation phase. The anisotropy for mechanical parameterization has also some influence, in particular through HM couplings. These HM couplings have the potential to be very significant in terms of providing confidence in describing the experimental observation, and should be considered for further investigation.

关键词： Hydro-mechanical (HM) coupling Numerical modelling Anisotropy Mont Terri Underground Research Laboratory (URL) Ventilation experiment (VE) argillite

Microstructural evolution and physico-chemical behavior of compacted clayey soil submitted to an alkaline plume

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Journal of Rock Mechanics and Geotechnical Engineering 2010年第2期2卷 169-177页

作者： D.Deneele O.Cuisinier V.Hallaire F.Masrouri Laboratoire Central des Ponts et Chaussées Nancy Université UMR INRA/Agrocampus

In the French concept of deep nuclear waste repositories,the galleries should be backfilled with excavated argillite after the site has been *** additives like lime could be used to improve the mechanical characteristics of the *** thousands of years,the degradation of the concrete lining of the galleries will generate an alkaline solution（pH value 12） that will diffuse through the *** study presents the effect of a saturated Ca（OH）_2 solution circulation through lime-treated sample at 60 ℃ for 3,6 and 12 months,*** effect of such circulation on the lime-treated Manois argillite（MA） was assessed by petrographical examination coupled to image analysis and scanning electron microscopy（SEM） equipped with energy dispersive X-ray（EDX） analyser of soil *** objective of this study is to make the link among the mineralogical transformations,the textural and mechanical changes produced in the compacted clayey soil as a consequence of the alkaline solution circulation.

关键词： argillite lime treatment petrographical examination scanning electron microscopy(SEM) image analysis microstructure