极细颗粒黏土渗流的微电场效应分析

采用渗流固结法试验结合颗粒表面电位分析,研究极细颗粒黏土的渗流的微电场效应,在相同试验条件下完成了5种含不同百分比的人工高岭土与人工膨润土的试样的渗流特性测试。测试结果表明,微孔渗流的微电场效应对极细颗粒黏土的渗流特性有相当显著的影响,随着孔隙液离子浓度的升降或土颗粒表面电位的增减,试样的渗透系数会随之发生改变;在相同的孔隙液离子浓度下,随着膨润土相对含量的增加,试样的渗透系数随之降低。对科威特软土的渗流固结试验证实了人工土的微电场效应的产生机制与变化规律同样适用于天然软土。试验结果分析认为,在黏土-水-电解质系统的相互作用下,黏土矿物通过土颗粒表面的结合水影响试样的渗流特性,而土颗粒表面电荷的微电场作用是极细颗粒黏土渗流特性改变的内在原因之一。     

均质非饱和土一维稳态流水头垂直分布的解析解

渗流场水头分布计算是进行渗流量和渗流水力坡降计算的基础,准确、有效地求取渗流场水头分布是渗流计算的关键环节。对均质非饱和土体一维稳态流的流动方程进行分析,考虑到渗透系数是与基质吸力相关的函数,通过数学变换,给出了稳定渗流场的解析通式,并基于渗透性函数中的Gardner模型,给出了非饱和土一维稳态流水头垂直分布的解析解。该解析通式表明,均质非饱和土一维稳态流水头垂直分布主要受地表水头、深度和流动率3个因素控制。分别计算了一维稳态蒸发条件下粉土和黏土两种典型土类水头沿垂直方向的分布。计算结果表明：稳态蒸发条件下粉土层和黏土层内的水头分布表现出相似的变化规律,即自地表至地下水位处随着土层深度的增加,水头分布呈现出加速递减的趋势;在相同的蒸发条件下,对于相同深度处的黏土和粉土而言,黏土层内水头更高些;对同一种土类而言,在较大的蒸发状态下同一深度处土层内水头更高。反之,则较低。     

求解热质输运—反应体系动力学模型的指数拟合有 …

热质输运－反应体系对于热液成矿,污染物迁移等均十分重要,该体系包括热质输运,流体渗流,地球化学平衡计算,多组分化学反应－输运过程耦合等动力学过程。介绍了求解热质输运－反应动力学是数拟合有限体积方法,并编制了相应的计算机软件。     

黏土岩温度-渗流-应力耦合特性试验与本构模型研究进展

高放废物处置库、垃圾填埋场等工程中常常涉及到温度场（T）、渗流场（H）和应力场（M）的耦合作用的问题。从试验和理论模型两个角度综述国内外黏土岩温度-渗流-应力耦合特性的研究进展,主要包括其传热特性、温度影响下的渗流特性、变形、强度、蠕变特性。在此基础上,重点分析了黏土岩水-热迁移模型以及热-力耦合本构模型的适应性。基于上述认识,通过试验研究了比利时Boom clay在温度作用下的强度、渗透性、蠕变性等特征。结果表明：随着温度升高,Boom clay的强度有所降低,渗透性显著增强,蠕变速率明显加快。提出了适用于Boom clay的THM耦合弹塑性损伤模型,计算结果验证了模型能合理反映温度的影响。最后,探讨了黏土岩THM耦合机理研究的不足和今后的研究方向。     

渗流的PFC-CFD耦合细观数值模拟

本文针对饱和多孔介质中渗流特点,在分析渗流连续介质力学模型的基础上,采用描述多孔介质中固相颗粒和液相流体耦合的细观力学模型,其中固相颗粒采用离散元的颗粒流理论(PFC)模拟,液相流体通过求解平均Navier-Stokes方程的计算流体动力学(CFD)技术计算,并利用建议的模型对二维渗流问题进行了模拟验证。数值模拟结果表明,采用PFC-CFD耦合细观力学模型能够描述从低雷诺流到高雷诺流范围很大的流体运动,可以用于多孔介质中的渗流问题分析。     

极细颗粒黏土渗流离子效应的试验研究

采用常规固结仪对孔隙液离子浓度对极细颗粒黏土渗流固结特性的影响进行试验研究,在相同试验条件下进行了4组孔隙液含NaCl浓度不同的膨润土试样固结性质的测试,得到了各试样的固结曲线,求得相应的固结系数,再由固结系数求得相应的渗透系数。通过对各组试样的渗透系数对比分析,结果表明,孔隙液离子浓度对土体的渗流性质有重要影响,土体的渗透系数随孔隙液离子浓度的增加而增大,存在明显的离子效应。试验结果分析认为,黏土颗粒表面的扩散双电层厚度随离子浓度变化而变化,可能是产生离子效应的主要原因。试验结果有助于分析土体渗流离子效应的起因,对改进和完善现有渗流固结计算理论有一定指导意义。     

岩体裂隙网络非线性非立方渗流研究与应用

裂隙岩体渗流与岩体其他分析密切相关。岩体裂隙网络渗流理论最初主要是建立在线性立方定律的基础基上的,当裂隙水头较大或者流速较大时,裂隙水流不再满足线性立方定律,此时如仍用线性立方水流分析,无疑将会给渗流分析带来较大的误差,甚至引起工程事故。当裂隙水流不满足线性立方定律时,研究这种渗流自身的规律则是非常重要的,也是必要的。通过研究裂隙网络稳定和非稳定情况下的非线性渗流、非立方渗流规律,得出以下结论：①当渗流规律偏离线性渗流较远时,按非线性渗流计算出的水头分布和流量与线性渗流相差较大;当偏离不远时,计算出的水头分布和流量与线性渗流相差较小,可近似简化为线性渗流分析;②当渗流偏离立方渗流较远时,按非立方渗流计算出的水头分布和流量与立方渗流相差较大;当偏离不远时,计算出的水头分布和流量与立方渗流相差较小,可近似简化为立方渗流分析;③对于非线性非立方渗流,应综合考虑非线性与非立方两种因素对渗流的影响。     

白云母—流体界面盐离子分布的计算模拟研究:对离子地球化学循环的启示

黏土矿物是表生土壤、沉积物、碎屑岩结晶颗粒表面的常见矿物,常与地质流体处于共存状态。离子–水–黏土矿物的相互作用影响着表生环境的流体组成、元素输运、土壤有机质分馏和沉积物的力学特性等。通过分子动力学模拟认识离子在黏土矿物–流体界面的分布,是揭示黏土矿物参与离子地球化学循环过程的基础。以白云母为研究对象,使用分子动力学模拟和热力学计算方法,分析了白云母–碱金属盐溶液界面的离子吸附结构和静电作用特性。研究发现Na⁺离子在白云母表面形成了两个内球络合吸附层, K⁺、Cs⁺离子仅形成一个内球络合吸附层。内球络合吸附层外可以形成多个外球络合吸附层,表现为离子的层状吸附结构。增大盐浓度没有改变同种离子的吸附结构,仅改变吸附层分布的大小。定量对比了使用伞状采样方法计算的离子吸附自由能曲线和基于离子密度分布得到的自由能曲线,二者总体一致,基本确证了模拟采样的充足性。研究表明界面流体不能视为均一的介电环境。     

裂隙岩体渗流-传热耦合的复合单元模型

基于复合单元法建立了裂隙岩体渗流-传热耦合的复合单元模型。该模型前处理简便快捷,网格剖分不受限制,可依据裂隙的真实信息自动将其离散在单元内。其次,采用交叉迭代算法,对裂隙岩体的渗流场和温度场进行耦合分析,耦合算法不仅考虑了温度对流体运动黏度的影响,而且可计算裂隙中流体与相邻岩块间渗流-传热过程以及两者间的渗流量和热量交换。通过与已有近似解析解相比较,验证了复合单元耦合算法的可靠性。算例分析表明,渗流-传热耦合作用对裂隙岩体的渗流场和温度场均有一定的影响。分析了不同岩块热传导系数和裂隙开度对热能提取效率的影响,结果显示,岩块热传导系数越大、裂隙开度越大,低温流体从高温岩块中吸取的热能会较多,出口处流体温度下降得较快。     

储层岩石流动电位的电化学影响因素

利用储层岩石的流动电位特性描述油藏的流动特性已引起地球物理领域的关注。依据多孔介质中的双电层模型与毛管电化学理论,建立了渗流场、离子流场和电流场的耦合关系,数值模拟了泥质砂岩储渗特性和电化学因素对流动电位耦合系数的影响。结果表明:当考虑储层岩石中存在浓差极化效应时,流动电位耦合系数的绝对值随溶液浓度、阳离子交换量、孔隙度和渗透率的增大而增大;浓差极化效应对流动电位具有放大作用。     

Heterogeneous Fe(II) oxidation and zeta potential

The determination of electrophoretic mobility and zeta potential was used as a diagnostic tool, alongside kinetic experiments, to delineate between three plausible mechanisms for the heterogeneous oxidation of Fe(II) by dissolved oxygen. One of these mechanisms is dependant on the positive surface charge that exists on Fe(III) (oxy)hydroxide surfaces at pH values below the Iso-Electric Point (IEP). However, this mechanism can be disputed as catalysis is observed on Fe(III) (oxy)hydroxide surfaces above the IEP despite a negative zeta potential. As well as an IEP shift an overall reduction of the magnitude of the zeta potential is observed in samples of field Fe(III) (oxy)hydroxide collected from the Taff Merthyr mine water treatment site in South Wales, UK. Low zeta potentials determined in mine water treatment systems will have beneficial effects for particle coagulation and settling in passive mine water treatment systems.     

Formulation of a unified constitutive model for clays and sands

This paper presents a new generalized effective stress model, referred to as MIT-S1, which is capable of predicting the rate independent, effective stress–strain–strength behaviour of uncemented soils over a wide range of confining pressures and densities. Freshly deposited sand specimens compressed from different initial formation densities approach a unique condition at high stress levels, referred to as the limiting compression curve (LCC), which is linear in a double logarithmic void ratio, e, mean effective stress space, p′. The model describes irrecoverable, plastic strains which develop throughout first loading using a simple four-parameter elasto-plastic model. The shear stiffness and strength properties of sands in the LCC regime can be normalized by the effective confining pressure and hence can be unified qualitatively, with the well-known behaviour of clays that are normally consolidated from a slurry condition along the virgin consolidation line (VCL). At lower confining pressures, the model characterizes the effects of formation density and fabric on the shear behaviour of sands through a number of key features: (a) void ratio is treated as a separate state variable in the incrementally linearized elasto-plastic formulation: (b) kinematic hardening describing the evolution of anisotropic stress–strain properties: (c) an aperture hardening function controls dilation as a function of ‘formation density’; and (d) the use of a single lemniscate-shaped yield surface with non-associated flow. These features enable the model to describe characteristic transitions from dilative to contractive shear response of sands as the confining pressure increases. This paper summarizes the procedures used to select input parameters for clays and sands, while a companion paper compares model predictions with measured data to illustrate the model capability for describing the shear behaviour of clays and sands. Copyright © 1999 John Wiley & Sons, Ltd.     

Analysis of influencing factors of clay particle diffusion in electric double layer北大核心CSCD

双电层结构对研究黏土力学特性、冻土水分迁移等具有重要意义。为了探究不同影响因素对黏土颗粒扩散双电层电势分布的影响,借鉴Gouy-Chapman-Stern双电层理论,基于Nernst-Planck方程和Poisson-Boltzmann方程,利用数值软件COMSOL定量分析了温度、浓度、颗粒尺寸、颗粒形状以及溶液相对介电常数对扩散双电层电势分布的影响规律。研究表明：温度对电势分布的影响不明显,但随着温度以及Stern层厚度增加,黏土颗粒表面电势和Stern电势均增加;而随着溶液浓度以及相对介电常数减小,表面电势值增加;在矿物成分、表面电荷密度以及颗粒形状确定的情况下,尺寸对于扩散双电层电势分布的影响不显著;但颗粒的不规则形状对电势分布的影响较为明显,当颗粒形状存在夹角时,夹角处的表面电势远大于其他位置,且夹角越小,夹角处表面电势值越大。     

矿物-水界面的表面离子化和络合反应模式

表面络合模式已广泛应用于研究矿物表面吸附和溶解反应,尤其是(氢)氧化物和层状铝硅酸盐矿物。表面官能团是矿物参与表面络合反应的基本单元,(氢)氧化物矿物只具有表面羟基,而层状铝硅酸盐矿物除表面羟基外还具有离子交换位。矿物的表面电荷由永久结构电荷、配位表面电荷和离解表面电荷组成,各种零表面电荷状态可由不同的零电荷点来表征。恒电容模式、双层模式和三层模式是3种最常用的表面络合模式,它们在双电层结构、表面反应(质子化反应和络合反应)、表面电荷与质量平衡方程及应用范围上存在着一些差异。     

A three-scale model for pH-dependent steady flows in 1:1 clays

A new three-scale model to describe the coupling between electro-chemistry and hydrodynamics in non-swelling kaolinite clays in steady-state conditions is proposed. The medium is characterized by three separate nano-micro and macroscopic length scales. At the pore (micro)-scale the portrait of the clay consists of micro-pores saturated by an aqueous solution containing four monovalent ions (Na⁺, H⁺, Cl⁻, OH⁻) and charged solid particles surrounded by thin electrical double layers. The movement of the ions is governed by the Nernst–Planck equations and the influence of the double layers upon the hydrodynamics is modeled by a slip boundary condition in the tangential velocity governed by the Stokes problem. To capture the correct form of the interface condition we invoke the nanoscopic modeling of the thin electrical double layer based on Poisson–Boltzmann problem with varying surface charge density ruled by the protonation/deprotonation reactions which occur at the surface of the particles. The two-scale nano/micro model is homogenized to the macroscale leading to a precise derivation of effective governing equations. The macroscopic model is discretized by the finite volume method and applied to numerically simulate desalination of a clay sample induced by an external electrical field generated by the placement of electrodes. Numerical results indicate strong pH-dependence of the electrokinetics.     

A dual-porosity model for ionic solute transport in expansive clays

A microstructure model of dual-porosity type is proposed to describe contaminant transport in fully-saturated swelling clays. The swelling medium is characterized by three separate-length scales (nano, micro, and macro) and two levels of porosity (nano- and micropores). At the nanoscale, the medium is composed of charged clay particles saturated by a binary monovalent aqueous electrolyte solution. At the intermediate (micro) scale, the two-phase homogenized system is represented by swollen clay clusters (or aggregates) with the nanoscale electrohydrodynamics, local charge distribution, and disjoining pressure effects incorporated in the averaged constitutive laws of the electro-chemo-mechanical coefficients and the swelling pressure, which appear in Onsager’s reciprocity relations and in a modified form of Terzaghi’s effective principle, respectively. The microscopic coupling between aggregates and a bulk solution lying in the micropores is ruled by a slip boundary condition on the tangential velocity of the fluid, which captures the effects of the thin electrical double layers surrounding each clay cluster. At the macroscale, the system of clay clusters is homogenized with the bulk fluid. The resultant macroscopic picture is governed by a dual-porosity model wherein macroscopic flow and ion transport take place in the bulk solution and the clay clusters act as sources/sinks of mass of water and solutes to the bulk fluid. The homogenization procedure yields a three-scale model of the swelling medium by providing new nano and micro closure problems, which are solved numerically to construct constitutive laws for the effective electro-chemo-hydro-mechanical coefficients. Considering local instantaneous equilibrium between the clay aggregates and micropores, a quasisteady version of the dual-porosity model is proposed. When combined with the three-scale portrait of the swelling medium, the quasisteady model allows us to build-up numerically the constitutive law of the equilibrium adsorption isotherm, which governs the instantaneous immobilization of the solutes in the clay clusters. Moreover, the constitutive behavior of the retardation coefficient is also constructed by exploring its representation in terms of the local profile of the electrical double layer potential of the electrolyte solution, which satisfies the Poisson–Boltzmann problem at the nanoscale.     

A new methodology for computing ionic profiles and disjoining pressure in swelling porous media

A new two-scale computational model is proposed to construct the constitutive law of the swelling pressure which appears in the modified form of the macroscopic effective stress principle for expansive clays saturated by an aqueous electrolyte solution containing multivalent ionic species. The microscopic non-local nanoscale model is constructed based on a coupled Poisson-Fredholm integral equation arising from the thermodynamics of inhomogeneous fluids in nanopores (Density Functional Theory), which governs the local electric double layer potential profile coupled with the ion-particle correlation function in an electrolytic solution of finite size ions. The local problem is discretized by invoking the eigenvalue expansion of the convolution kernel in conjunction with the Galerkin method for the Gauss-Poisson equation. The discretization of the Fredholm equation is accomplished by a collocation scheme employing eigenfunction basis. Numerical simulations of the local ionic profiles in rectangular cell geometries are obtained showing considerable discrepancies with those computed with Poisson-Boltzmann based models for point charges, particularly for divalent ions in calcium montmorillonite. The constitutive law for the disjoining pressure is reconstructed numerically by invoking the contact theorem within a post-processing approach. The resultant computational model is capable of capturing ranges of particle attraction characterized by negative values of the disjoining pressure overlooked by the classical electric double layer theory. Such results provide further insight in the role the swelling pressure plays in the modified macroscopic effective stress principle for expansive porous media.     

Behavior of mercury in the supergene zone of geothermal deposits,southern Kamchatka

Mercury distribution was determined in all types of solid materials from the supergene zone of geothermal deposits in southern Kamchatka: rocks, hydrothermally altered rocks (metasomatic rocks), soils, soil—pyroclastic cover, bottom sediments of perennial and intermittent streams, hydrothermal clays, artificial siliceous precipitates, and iron sulfides formed owing to thermal water discharge from a well. The mercury content varies from background values for the Kurile-Kamchatka region in fresh rocks to high and extremely high values in hydrothermal clays and monomineralic pyrite samples. The sources, migration conditions, and concentration mechanisms of mercury were evaluated. Mercury is supplied to the surface of geothermal deposits and thermal fields by a deep hydrothermal flow and is concentrated on thermodynamic barriers in hydrothermal clays, siliceous sinters (silica gel), and soils showing high salinity owing to the deposition in them of silica, sulfates, and other compounds from a vapor-water mixture. Newly formed clay minerals, iron sulfides (pyrite), silica gel, and biological materials (peat) can probably efficiently sorb mercury under geothermal conditions at atmospheric pressure and temperatures from 20°C to 120°C.     

Gas-chromatographic investigations on dimethyldioctadecyl ammonium derivatives of different clay minerals

The gas-chromatographic behaviour (selectivity performance for cyclohexanebenzene and m-, p-xylenes pairs separation) of dimethyldioctadecylammonium complexes with kaolinite, fire-clay, halloysite, attapulgite, hectorite and various montmorillonites, nontronites and vermiculites has been investigated. The obtained data indicate the influence of specific surface and charge density on relative retention value (), and of substitution location (tetrahedral versus octahedral sheet) within the clay lattice on selectivity. Hence, derivatives with nontronites and vermiculites, that is the clay minerals where the principal lattice substitutions are predominantly occurring within the tetrahedral sheet and possessing the highest surface charge density, are very effective sorbents for gas-chromatographic use. The application of gas-chromatography as investigation tool of clays surface is suggested.     

Influence of gas generation in electro‐osmosis consolidation

This paper presents a numerical model for the elasto‐plastic electro‐osmosis consolidation of unsaturated clays experiencing large strains, by considering electro‐osmosis and hydro‐mechanical flows in a deformable multiphase porous medium. The coupled governing equations involving the pore water flow, pore gas flow, electric flow and mechanical deformation in unsaturated clays are derived within the framework of averaging theory and solved numerically using finite elements. The displacements of the solid phase, the pressure of the water phase, the pressure of the gas phase and the electric potential are taken as the primary unknowns in the proposed model. The nonlinear variation of transport parameters during electro‐osmosis consolidation are incorporated into the model using empirical expressions that strongly depend on the degree of water saturation, whereas the Barcelona Basic Model is employed to simulate the elasto‐plastic mechanical behaviour of unsaturated clays. The accuracy of the proposed model is evaluated by validating it against two well‐known numerical examples, involving electro‐osmosis and unsaturated soil behaviour respectively. Two further examples are then investigated to study the capability of the computational algorithm in modelling multiphase flow in electro‐osmosis consolidation. Finally, the effects of gas generation at the anode, the deformation characteristics, the degree of saturation and the time dependent evolution of the excess pore pressure are discussed. Copyright © 2016 John Wiley & Sons, Ltd.