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1.
ABSTRACT

The effect of sample scale represents a challenge when obtaining engineering parameters in the laboratory compared to those obtained in the field. This study aimed at contributing to existing knowledge numerically using the finite element software PLAXIS 2D. The investigations were analysed in terms of height scale (HS) and diameter scale (DS) through a series of laboratory tests. Its effect on compressibility parameters such as coefficient of consolidation (cv) was noted experimentally and showed that the sample scale greatly influences soil parameters most particularly at DS. The soil behaviour was found to be dependent on both DS and HS with a correlation factor of 0.650 and 0.062, respectively. The experimental data were validated in PLAXIS and a new proposed model was developed in PLAXIS 2D under the DS. The new proposed model developed was found to show no significant difference with the laboratory data.  相似文献   

2.
Many geoscientific fields use reactive transport codes to set up and interpret experiments as well as to understand natural processes. Reactive transport codes are also useful to give insights in the long term evolution of systems such as radioactive waste repositories or CO2 storage sites, for which experiments cannot reach the targeted time scale nor the dimension of those systems. The consideration of kinetic reaction rates is often required to reproduce correctly the geochemical and transport processes of interest. However, kinetic data are scattered in the literature, making data and selection a tedious task. Kinetic parameters on a single system are also highly variable depending on data choice, interpretation and chosen kinetic modelling approaches, thus making inter-comparison of modelling studies difficult. The present work aims at proposing a compilation of kinetic parameters to overcome part of above cited problems. The proposed selection was done (i) to ensure consistency of data selection criteria and data treatment and (ii) to ease the use of common kinetic parameters that are independent of the chosen geochemical modelling code. For those two reasons, the kinetic formalism of the transition state theory (TST) was chosen. The selection of minerals is currently limited to those present in clay rich rocks and cements, reflecting the effort made at predicting the evolution of radioactive waste underground storage systems. Still, the proposed compilation should also be useful for other applications such as CO2 sequestration.  相似文献   

3.
This paper presents a first attempt at the inclusion of some biological impacts and influences in the authors’ continued research on coupled transport phenomena through unsaturated porous media. The work presented here forms an extension to an existing coupled Thermo-Hydraulic-Chemical–Mechanical Model (THCM) to include the biological aspects, as a first attempt towards a new THCMB framework. The biological model incorporates biodegradation kinetics of organic substrates and resultant effects in the inorganic geochemistry. In order to achieve this, the biological aspects of the model are coupled to an equilibrium geochemical model following a two-step partial equilibrium approach. Additionally, of concern in contaminant/pollutant transport studies, including the biological aspects, is the effect on human health. This paper therefore also presents some aspects of a health impact analysis model adopted in this study.  相似文献   

4.
Organic geochemical analyses of fine-grained rocks from the 9.590 km Bertha Rogers No. 1 well have been carried out: total organic carbon, Soxhlet extraction and silica gel chromatography, C15+ saturated and aromatic hydrocarbon gas chromatography and mass spectrometry, pyrolysis, kerogen analysis, X-ray diffraction and visual kerogen analysis.Rocks ranged in age from Permian to Ordovician; the well has an estimated bottom hole temperature of 225°C. Some data from this study are inconsistent with conventional theories concerning the generation and thermal destruction of hydrocarbons. For example, appreciable amounts of C15+ gas-condensate-like hydrocarbons are present in very old rocks currently at temperatures where current theory predicts that only methane and graphite should remain. Also, substantial amounts of pyrolyzable C15+ hydrocarbons remain on the kerogen in these deeply buried Paleozoic rocks. This suggests, at least in somes cases, that temperatures much higher than those predicted by current theory are required for generation and thermal destruction of hydrocarbons. The data from this well also suggest that original composition of organic matter and environment of deposition may have a much stronger influence on the organic geochemical characteristics of fine-grained sediments than has previously been ascribed to them. The results from this well, from other deep hot wells in which temperatures exceed 200°C, and from laboratory experiments, suggest that some of the basic concepts of the generation and maturation of petroleum hydrocarbons may be in error and perhaps should be reexamined.  相似文献   

5.
We present a new Bayesian framework for the validation of models for subsurface flows. We use a compositional model to simulate CO2 storage in saline aquifers, comparing simulated saturations to observed saturations, together with a Bayesian analysis, to refine the permeability field. At the laboratory scale, we consider a core that is initially fully saturated with brine in a drainage experiment performed at aquifer conditions. Two types of data are incorporated in the framework: the porosity field in the entire core and CO2 saturation values at equally spaced core slices for several values of time. These parameters are directly measured with a computed tomography scanner. We then find permeability fields that (1) are consistent with the measured parameters and, at the same time, (2) allow one to predict future fluid flow. We combine high performance computing, Bayesian inference, and a Markov chain Monte Carlo (McMC) method for characterizing the posterior distribution of the permeability field conditioned on the available dynamic measurements (saturation values at slices). We assess the quality of our characterization procedure by Monte Carlo predictive simulations, using permeability fields sampled from the posterior distribution. In our characterization step, we solve a compositional two-phase flow model for each permeability proposal and compare the solution of the model with the measured data. To establish the feasibility of the proposed framework, we present computational experiments involving a synthetic permeability field known in detail. The experiments show that the framework captures almost all the information about the heterogeneity of the permeability field of the core. We then apply the framework to real cores, using data measured in the laboratory.  相似文献   

6.
The rise of vascular land plants in the Paleozoic is hypothesized to have driven lower atmospheric CO2 levels through enhanced weathering of Ca and Mg bearing silicate minerals and rocks. However, this view overlooks the co-evolution of roots and mycorrhizal fungi, with many of the weathering processes ascribed to plants potentially being driven by the combined activities of roots and fungi. Here mesocosm scale controlled laboratory experiments quantifying the effects of plant and fungal evolution on silicate rock weathering under ambient and elevated CO2 concentrations are described. A snapshot is presented of C allocation through roots and mycorrhizal fungi and biological activity associated with geochemical changes in weathered mineral substrates via transfer of elements from solid phases into solution.  相似文献   

7.
Won  Jongmuk  Lee  Junghwoon  Burns  Susan E. 《Acta Geotechnica》2021,16(2):421-432

Understanding particle transport in porous media is critical in the sustainability of many geotechnical and geoenvironmental infrastructure. To date, the determination of the first-order rate coefficients in the advection–dispersion equation for simulating attachment and detachment of particles in saturated porous media typically has been relied on the result of laboratory-scale experiments. However, to determine attachment and detachment coefficients under varied hydraulic and geochemical variables, this method requires a large experimental matrix because each test provides only one set of attachment and detachment coefficients. The work performed in this study developed a framework to upscale the results obtained in pore-scale modeling to the continuum scale through the use of a pore network model. The developed pore network model incorporated variables of mean particle size, the standard deviation of particle size distribution, and interparticle forces between particles and sand grains. The obtained retention profiles using the pore network model were converted into attachment coefficients in the advection–dispersion equation for long-term and large-scale simulation. Additionally, by tracking individual particles during and after the simulation, the pore network model introduced in this study can also be employed for modeling the clogging phenomenon, as well as fundamental investigation of the impact of particle size distribution on particle retention in the sand medium.

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8.
The complex reactions between high saline solutions and toxic chemical wastes were investigated by means of laboratory experiments and geochemical modelling. The specific boundary conditions of an underground repository in salt formations were taken into account. In order to determine the chemical equilibrium compositions of the resulting solutions a new leaching procedure was developed and successfully employed with several toxic wastes. The results for a fly ash waste stemming from a glass smelting furnace are given in detail. Zinc and cadmium are the two most prominent heavy metals, that accumulate significantly in the leachates. In order to gain an insight into the complex dissolution and precipitation processes in such multi-component systems, geochemical modelling was performed using the program code EQ3/6 and the Pitzer formalism for calculating the activity coefficients. The thermodynamic database used was extended and Pitzer coefficients for Zn and Cd in high saline solutions were derived from literature data and added to the database. The results of the geochemical modelling of the investigated reactions were in good agreement with the experimental data. On this basis the maximum concentrations that can be leached from the investigated fly ash into a Mg-rich saline solution, that is typical for a salt repository in Northern Germany, are predicted to be 0,181 mol/kg H2O zinc and 0,00317 mol/kg H2O cadmium, respectively.  相似文献   

9.
Functional relationships correlating particle filtration coefficients and porewater ionic strength are herein proposed and validated, based on deposition experiments of micrometer-sized particles onto siliceous sand. Experiments were conducted using one-dimensional laboratory columns and stable monodisperse aqueous suspensions of negatively charged latex particles with a mean size of 1.90 μm. The role of ionic strength was systematically investigated and six different monovalent salt concentrations (1, 3, 10, 30, 100, 300 mM) were employed by addition of sodium chloride to the aqueous solution. A mathematical advection–dispersion-deposition transport model was adopted assuming that attachment and detachment of particles in the porous medium are concurrent mechanisms of particle filtration, and including a Langmuir-type blocking function to account for availability in deposition sites. The system of equations modeling colloid transport was solved numerically. Attachment rate and detachment rate coefficients were thereby determined for each employed ionic strength, as well as a blocking coefficient in the form of a maximum particle concentration in the solid phase. Therefore, functional relationships expressing the dependence of these coefficients on ionic strength were proposed, based on literature findings and present experimental observations. The existence of a critical salt deposition concentration (and release concentration) separating a favorable attachment (and detachment) regime from an unfavorable condition is assumed. In respect to the blocking coefficient, a power–law dependence on ionic strength is hypothesized. The proposed functional relationships proved adequate to reproduce the coefficient trends extrapolated from data fitting by the transport model. They may represent a powerful tool to describe and predict microparticle mobility in saturated porous media if embedded a priori in the related mathematical transport models.  相似文献   

10.
This paper addresses the problem of the interpretation of geochemical laboratory experiments aimed at investigating partially molten rocks. The material of the terrestrial planets is differentiated at a certain stage of their evolution. In a gravity field, heavy and light particles move in a melt in different directions. This results in the formation of layers with different chemical and petrographic compositions in laboratory experiments and in planetary interiors. A density inversion appears in these layers under certain conditions. The dynamics of partially molten rocks was investigated using two analytical models. One of them is a problem of two bodies in a liquid governed by hydrodynamic Stokes equations. The second model describes the relative motion of solid particles in different directions in a viscous porous layer.  相似文献   

11.
《Applied Geochemistry》1994,9(5):583-595
A steady-state geochemical model has been developed to study water-rock interactions controlling metal release from waste rock heaps at the Aitik Cu mine in northern Sweden. The Cu release in drainage waters from the site is of environmental concern. The waste rock heaps are treated as single completely mixed flow-through reactors. The geochemical model includes kinetices of sulphide and primary silicate mineral weathering, heterogeneous equilibrium with secondary mineral phases and speciation equilibrium. Field monitoring of drainage water composition provides a basis for evaluation of model performance.The relative rate of oxidative weathering of sulphides and dissolution of primary silicate minerals, using published kinetic data, are consistent with net proton and base cation fluxes at the site. The overall rate of Fe2+ oxidation within the heap is three orders of magnitude faster than that which could be explained by surface-catalysed reaction kinetics. This suggests significant activity of iron-oxidizing bacteria. The absolute weathering rates of sulphides and silicate minerals, normalized to a measured BET surface area, are approximately two orders of magnitude lower at field scale than published rates from laboratory experiments. Because of the relative absence of carbonate minerals, the weathering of biotite and plagioclase feldspar are important sources of alkalinity.  相似文献   

12.
通过野外地质调查与机器学习方法的有机融合,提出了一种基于梯度提升决策树算法的岩性单元填图方法。研究以多龙矿集区为模型试验区,选择1∶5万勘查地球化学数据为基础预测数据,以1∶5万区域地质图为参考,进行基于梯度提升决策树算法的岩性预测填图模型试验。首先选择研究区内小范围空白区开展野外填图,建立原始数据集并初步构建岩性单元与预测数据对应关系;其次利用机器学习方法对预测数据进行多分类任务,进而开展目标填图区预测填图工作;最后通过概率选区选定概率较低目标区,开展进一步的小范围野外地质调查填图,对原始数据和知识库进行补充,迭代循环以上流程,直至预测填图达到要求。试验显示,随着迭代次数的增加,模型精度不断提高,并在7次迭代后模型准确率达到87%。该方法强调在实际应用中野外地质调查与基于机器学习预测填图的深度融合,以及野外实地工作在整个流程中的重要性和不可或缺性;同时能够充分挖掘已有数据资料的有用信息,用于辅助修正已有岩性填图内容,或根据已勘探区资料对邻近的未勘探区进行岩性分类,有效减少野外填图工作量,是对岩性填图方法、地质单元定量预测识别的有益探索,为区域地质填图工作提供了新的参考思路和辅助手段。   相似文献   

13.
PGE的地球化学性质及其分配系数的实验研究进展   总被引：2，自引：0，他引：2  
随着现代化仪器的发展和分析方法的改进,对PGE的分析技术已经取得突破。PGE已经成为岩石学、矿床学和地球化学的一个重要研究领域。本文系统综述了PGE和Au元素的分配系数实验的研究进展,区分和总结了适用于岩浆硫化物矿床的实验数据。根据此实验数据发现仅用硫化物液相不混熔模型难以解释岩浆硫化物矿床的高PGE_Au含量,提出应该增加考虑岩浆后期的熔体或流体活动对PGE_Au元素的再富集过程。同时介绍一些关于PGE数据处理的常用方法及其应用。  相似文献   

14.
We present new geochemical data (major- and trace-elements, as well as Sr and Nd isotopic compositions) of volcanic rocks erupted from Popocatépetl volcano during the volcanic event from December 2000 to January 2001. These data along with an exhaustive compilation of geochemical and Sr, Nd, and Pb isotope data reported for Popocatépetl rocks and nearby volcanic areas are used to examine the origin and geochemical evolution of the magmas in the central Mexican volcanic belt (CMVB). During this period of volcanic eruptions Popocatépetl produced ash columns as high as 7 km. Pyroclastic flows and lahars were observed after the completion of the activity. Samples of banded pumice and a bomb fragment transported by the lahar were chemically analysed for this work. Rocks show an andesitic composition with 58.5–61.7 wt.% SiO2 and 5.9–4.0 wt.% MgO. Contents of large ion lithophile elements (LILE), rare-earth elements (REE) and Zr are nearly constant through the compositional range. No significant Eu anomaly is present, but the samples show Nb-anomaly relative to LILE and high-field strength elements (HFSE). Nd- and Sr-isotopic compositions of these samples range from 143Nd/144Nd = 0.51291 to 0.51287 and 87Sr/86Sr = 0.70399 to 0.70422. Comparison of Popocatépetl products with volcanic rocks from the nearby areas shows that the magmas in CMVB were generated in a heterogeneously veined-mantle source enriched in LILE, HFSE, and REE. Additional crustal assimilation as well as fractional crystallization could account for the great chemical variability of rocks in the CMVB. Statistical comparison of the geochemical compositions of the volcanic products ejected from 1994 to 2000 to those ejected during the 2001 event shows that most geochemical parameters (major- and trace-elements, normative minerals, Sr and Nd isotopic composition, as well some elemental ratios) present no statistically significant differences. Statistically significant differences in the mean only were computed for the major-elements SiO2, FeO, MgO, CaO, and K2O, as well as for the rare-earth elements Nd, Sm, Eu, Gd, Dy, Ho, Tm, and Yb.  相似文献   

15.
A model was developed, to describe miscible grout propagation in a saturated deformable porous medium, based on Bear's statistical model with spatial volume averaging. In a previous paper, the model was first successfully confronted to one‐dimensional laboratory experiments. In the present paper, the numerical model is used to simulate practical grouting operation in a cylindrical injection model. The cylindrical injection model lends itself to study main flow and propagation character istics for a dispersed suspension‐type grout, under axisymmetric conditions close to real scale conditions. Comparison between numerical solutions and experimental results is essential to confirm the validity and accuracy of the proposed model from a phenomenological standpoint. The numerical model performances show that the underlying mathematical model constitutes a realistic predictive model reproducing most prominent features during injection of a suspension‐type grout into a deformable porous medium. The basic mechanism by which injected miscible grout permeates a soil mass is discussed in detail. Such a tool leads to quality control criteria for grouting on a theoretical basis, which complements existing criteria acquired through engineering practice. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

16.
The Eocene Farim‐Saliquinhé phosphate mineralization (FSPM) is a buried sedimentary deposit located in the northern part of Guinea‐Bissau, discovered and spatially constrained during the 1980s by the French Geological Survey (BRGM). In the present work some of the data collected at that time are reworked in the framework of the development of a 3D geological and geochemical model of this mineralization. We show the usefulness of two classical multivariate statistical methods – principal component analysis (PCA) and cluster analysis (CA) – applied to eight geochemical variables (P2O5, SiO2, Al2O3, Fe2O3, CaO, MgO, F and CO2) measured in 247 samples from phosphate facies, for differentiation of samples taken from the different phosphate facies recognized in the FSPM, namely the main ore FPA (30 to 35% high grade phosphate), the calcareous low grade phosphate FPB (10 to 20% P2O5) (both Lutetian), and a mineralized Upper Eocene to Lower Oligocene cover (mainly including the FPO level and a silico‐aluminous phosphate bed), overlying the FPA, which can also be considered a third set of phosphate facies associated with the FSPM.  相似文献   

17.
We consider a stationary flow of an incompressible non-Newtonian flow through a porous medium, induced by an injection velocity when inertial effects are negligible. At the pore scale, the governing equations are based on a nonlinear relation between the stress and the rate of deformation. In such a situation, the limit problem obtained when the pore size tends to zero, is called the homogenized problem that leads to the filtration law. This filtration law is given by a non-linear system coupling a local problem on a typical cell of the porous medium to a global problem at the scale of the whole porous medium. We propose, in this work, a numerical method to solve this homogenized problem and apply this method when the velocity dependent viscosity is given by the power law. Finally, we propose some numerical experiments to illustrate our approach.  相似文献   

18.
The geological features of the pegmatites from the Borborerna Pegmatitic Province (BPP) are described, combining data from the literature with new field and laboratory observation. A geochemical study was performed against this geological background to test the crystallization model of mineralized pegmatites against barren pegmatites and to compare the BPP with other provinces, fields or individual pegmatites throughout the world. The field evidence (mode of emplacement, textural relationships, zonation and mineralogy) as well as the geochemical characteristics support the pegmatite crystallization model proposed by London (1990). The geochemical and mineralogical evidence places these pegmatites as “medium Ta-mineralized” compared to other pegmatite provinces.  相似文献   

19.
《Geochimica et cosmochimica acta》1999,63(19-20):3301-3310
The weathering rate of sedimentary organic matter in the continental surficial environment is poorly constrained despite its importance to the geochemical carbon cycle. During this weathering, complete oxidation to carbon dioxide is normally assumed, but there is little proof that this actually occurs. Knowledge of the rate and mechanisms of sedimentary organic matter weathering is important because it is one of the major controls on atmospheric oxygen level through geologic time.We have determined the aqueous oxidation rates of pyrite-free bituminous coal at 24° and 50°C by using a dual-cell flow-through method. Coal was used as an example of sedimentary organic matter because of the difficulty in obtaining pyrite-free kerogen for laboratory study. The aqueous oxidation rate obtained in the present study for air-saturated water (270 μM O2) was found to be on the order of 2 × 10−12 mol O2/m2/s at 25°C, which is fast compared to other geologic processes such as tectonic uplift and exposure through erosion. The reaction order with respect to oxygen level is 0.5 on a several thousand hour time scale for both 24° and 50°C experiments. Activation energies, determined under 24° and 50°C conditions, were ≈40 kJ/mol O2 indicating that the oxidation reaction is surface reaction controlled.The oxygen consumption rate obtained in this study is two to three orders of magnitude smaller than that for pyrite oxidation in water, but still rapid on a geologic time scale. Aqueous coal oxidation results in the formation of dissolved CO2, dissolved organic carbon (DOC), and solid oxidation products, which are all quantitatively significant reaction products.  相似文献   

20.
Increasing the prediction rate in the identification of mineralization zones using the stream sediment geochemical data is an essential issue in the regional exploration stage. The various univariate (such as fractal and probability plot (PP) methods) and multivariate methods (such as principal component analysis (PCA)) have been performed for interpreting the geochemical data and detecting the mineralization areas. In this study, a new geochemical criterion named geochemical anomaly intensity index (GAII) was proposed for geochemical anomaly mapping. This approach was developed based on the PCA method and the catchment basin coefficient (CBC). The GAII as a weighted geochemical index is calculated using the mineralization principal component (MPC) scores and CBC. GAII can be mapped and utilized for geochemical anomaly mapping and detecting the mineralization areas. Besides, GAII can identify paragenesis elements better than the current methods. In this research, GAII was successfully used to generate geochemical anomaly maps on shear zone gold mineralization in the southwest of Saqqez, NW Iran. The geochemical data have been divided into three groups based on catchment basins and the host rock type. Then the MPCs and paragenesis elements of Au mineralization have been obtained individually using PCA. Three mineralization paragenesis groups consisting of (Au, Sn), (Au, W), and (Au, As, Sb and Ba) have been recognized for different catchment basins of the southwest of Saqqez district using PCA. GAII was calculated and mapped based on the CBC(Au, Sn), CBC(Au, W), CBC(Au, As, Sb, Ba), and their MPC scores. GAII accurately detected the Au mineralization zones and improved the geochemical anomaly map in this area compared to the PP method, concentration-area fractal model, and U-spatial statistics method. The results demonstrated that GAII was successfully used for (a) identifying the mineralization paragenesis elements, (b) intensifying the geochemical anomaly, and (c) increasing the prediction rate of mineralization zones. The shear zone gold mineralization areas in the southwest of Saqqez district were effectively detected using this new data analysis approach. GAII has provided better results than the current PP method, concentration-area fractal model, and U-spatial statistics method.  相似文献   

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