多孔介质中溶质有效扩散系数预测的分形模型

依据分形理论和方法,探索溶质在多孔介质中的有效扩散系数的替代预测方法。在多孔介质溶质扩散的弯曲毛细管束模型的基础上,以分形维数作为介质的基本几何特性参数,建立了多孔介质中溶质扩散的分形毛细管束模型,推导出了溶质有效扩散系数与介质孔隙度之间的幂定律关系式,幂指数是介质孔隙分维和表面分维的函数,反映了介质孔隙体积的层次分布与孔隙通道曲折程度对扩散的影响。对粘性土的分形维数测定数据和有效扩散系数试验测定数据的分析表明,利用该关系式预测多孔介质中溶质的有效扩散系数是较为准确可靠的。     

A new matrix for multiphase couplings in a membrane porous medium

The empirical Darcy's law of water transport in porous media, Fick's law of chemical diffusion, and Fourier's law of thermal transport have been widely used in geophysics/geochemistry for over 150 years. However, the strong couplings between water, temperature, and chemicals in a membrane porous medium have made these laws inapplicable and present a significant hurdle to the understanding of multiphase flow in such a material. Extensive experiments over the past century have observed chemical osmosis and thermal osmosis, but a model for understanding their underlying physicochemical basis has remained unavailable, because of the highly cross‐disciplinary and multiscale‐multiphase nature of the coupling. Based on the fundamental principles of nonequilibrium thermodynamics and mixture coupling theory, a rigorously theoretical and mathematical framework is proposed and a general model accounting for all of the coupled influences is developed. This leads to a simple and robust mathematical matrix for studying multiphase couplings in a membrane porous medium when all chemical components are electrically neutral.     

泥石流堆积过程数值模拟及防灾效益评估方法

根据动量守恒和质量守恒原理 ,研究建立了泥石流堆积过程的数学模型 ,运用有限差分法求解数学模型 ,用以模拟泥石流堆积的动态过程。在此基础上 ,结合云南省东川市深沟泥石流堆积区的实际情况 ,对泥石流灾害的危险范围和程度进行了分析评价 ;结合各类受灾体经济损失评价 ,对比防灾工程造价 ,进行了减灾效益分析评价。     

Solute transfer during consolidation based on a solid‐fluid‐solute coupling model

The migration of contaminant through soil is usually modeled using the advection‐dispersion equation and assumes that the porous media is stationary without introducing a constitutive equation to represent soil structure. Consequently, time‐dependent deformation induced by soil consolidation or physical remediation is not considered, despite the need to consider these variables during planning for the remediation of contaminated ground, the prediction of contaminated groundwater movement, and the design of engineered landfills. This study focuses on the numerical modeling of solute transfer during consolidation as a first step to resolve some of these issues. We combine a coupling theory‐based mass conservation law for soil‐fluid‐solute phases with finite element modeling to simulate solute transfer during deformation and groundwater convection. We also assessed the sensitivity of solute transfer to the initial boundary conditions. The modeling shows the migration of solute toward the ground surface as a result of ground settlement and the dissipation of excess pore water pressure. The form of solute transport is dependent on the ground conditions, including factors such as the loading schedule, contamination depth, and water content. The results indicate that an understanding of the interaction between coupling phases is essential in predicting solute transfer in ground deformation and could provide an appropriate approach to ground management for soil remediation.     

储层特低渗透成因分析与评价——以安塞油田沿25区块为例

应用测井资料和铸体薄片、扫描电镜、X 衍射、粒度分析、压汞等化验分析资料综合研究了安塞油田沿25区块长6储层的特低渗透成因和影响因素,并评价了储层储集性能。分析表明,该区块储层物性总体较差,发育粒间孔、溶蚀孔,孔隙结构类型属小孔隙、微细喉道型。其特低渗透成因主要受沉积作用和成岩作用的共同影响,具体表现为：不同沉积微相储层的物性差异较大,软组织含量大、粒度细和成分成熟度较低是造成储层特低渗透特征的主要原因。同时成岩压实、胶结作用使得储层的孔隙度、渗透性进一步减小、变差,而溶蚀作用和成岩缝的产生又在很大程度上改善了储层的特低渗透特征。根据物性和孔隙结构参数分析,将研究区储集岩分为3类,水下分流河道与河口坝砂体是主要储层分布相带。     

多孔介质中水泥浆三维锋面特征研究

深层渗滤效应普遍存在于多孔介质的渗透注浆过程中,并起着非常重要的作用。基于质量守恒方程、线性滤过定律、渗流连续性方程及Darcy定律,建立了水泥浆三维锋面的理论模型;通过现场试验,研究了水泥浆三维锋面扩散运移及沉积层渗透系数的变化规律,并将试验值与模型理论值进行了对比分析。结果表明,沉积层渗透系数随水泥浆锋面的扩散运移动态变化;当注浆压力恒定时,水灰比越小,深层渗滤效应越显著,浆液扩散距离相应越短;相同扩散距离时,受重力效应的影响,注浆点源之上的沉积层渗透系数大于注浆点源之下的沉积层渗透系数;浆液扩散距离及固定位置处的沉积层渗透系数均与水灰比呈正相关。研究成果可指导工程设计,具有一定的实际应用价值。     

考虑固结效应的溶质传输研究

传统的孔隙介质水动力学采用对流-扩散方程,研究溶质在流体中的迁移。在这个过程中,孔隙介质被认为是不变形的,因而是一个稳态问题。针对二维情况下孔隙介质变形对溶质传输的影响,给出了考虑孔隙介质固结效应的溶质传输方程,并且探讨了该类问题的求解方法。     

Mathematical and numerical filtration–advection–dispersion model of miscible grout propagation in saturated porous media

The development of a predictive model of behaviour of porous media during injection of miscible grout, taking into account convection, dilution and filtration of grout solution with interstitial water, as well as consolidation aspects, is presented. Model assumptions are reviewed and discussed first. During the establishment of the model, we insist on surface terms and their physical relevance in expressing adsorption effects. Constitutive laws such as Fick's law for diffusive mass transport, hydrodynamic dispersion tensor dealing with miscibility, are modified by taking into account filtration effects. A new surface term appears in mass balance equations as a consequence of filtration. According to the filtration laws used, an initial filtration rate is estimated on the basis of a one‐dimensional experimental campaign. The field equations are discretized by using Galerkin finite element and θ‐scheme standard method. For transport equation, Streamline Upwind Petrov Galerkin method is employed to prevent numerical oscillations. Lastly, confrontation of numerical results with laboratory experiments constitutes a first step to validate the model on a realistic basis. Copyright © 2001 John Wiley & Sons, Ltd.     

基于流网单元的污染物优势运移数值模型

垃圾填埋场滤出液、入侵海水、核废物及生产生活废水等污染物随地下水的迁移威胁人类生存。地下水渗流的随机性导致溶质运移问题更加复杂。根据流网特点,利用流线与水头等势线对求解域进行离散,基于质量守恒原理建立流网单元内溶质浓度求解的隐式有限体积差分格式。基于多孔介质孔隙流速分布规律,利用蒙特卡洛法建立流管单元随机流速场进行溶质运移过程的数值模拟,最后根据数值模拟和模型试验的结果对比,验证了数值模拟方法的准确性。基于流网单元的数值模型中沿流线方向的物质交换由对流和扩散共同作用,而流管间的物质交换只有扩散作用,因此,可在不使用弥散系数下进行污染物运移的模拟。引入随机方法确定流管内流速为研究非均匀流场中染污物的优势迁移提供了新的思路。     

电场-渗流场-应力场耦合的电渗固结数值分析

在非饱和土多孔介质力学理论的基础上,根据电荷守恒原理、质量守恒原理、应力平衡方程、达西定律以及欧姆定律,推导了考虑电场、渗流场以及应力场相互耦合作用的电渗固结理论方程。采用Galerkin加权余量法对电渗固结理论方程进行空间离散,得到其有限元计算列式,编制了相应的计算程序,对室内电渗模型试验进行了数值模拟。结果表明,数值模拟与试验结果基本吻合,表明该电渗固结理论方程能够定量预测电渗固结过程中土体的孔隙水压力和位移发展规律。     

Experimental and numerical study of pollution process in an aquifer in relation to a garbage dump field

The water quality of shallow aquifers that have direct relationship to human heath and ecological safety has been seriously threatened by widespread dumping of industrial solid waste, urban and rural garbage. A garbage dump field with hydrogeological, environ-geological characteristics typical of the Beijing plain was selected for investigation. A hydrogeological model was constructed and the equations used to describe pollutant transport in one-dimensional (1D) steady, uniform groundwater flow to investigate the transport/diffusion processes. In addition to the coefficients for calculation, diffusion coefficient and other coefficients of the aquifer were obtained by conducting in situ diffusion experiments and sample tests. Velocity and scope of pollutant transport/diffusion process were calculated. Accordingly, the real pollution situation in the aquifer was evaluated through in situ drilling and sample testing. Transport/diffusion processes of pollutants within the aquifer abide by the solute equation applicable to 1D steady flow. The transport and diffusion dominate in the direction of groundwater flowing at a speed of about 120 m per year. Comparably, the lateral diffusive width is much smaller. Pollution degree decreases by the law of Y=1.08 exp(33.533/X), where Y is the distance from the garbage dump field and X is the overall pollution index.     

非火山地热区玛旁雍热田土壤CO_2脱气研究

地热活动是地球脱气的重要形式之一,其过程常伴随大量温室气体排放。选取非火山地热区西藏玛旁雍热田作为研究对象,基于菲克扩散定律对地热田区土壤CO_2脱气量进行评估。结果表明:该区一般土壤CO_2脱气通量为0.167~0.771 kg/(m2·a),含喷气孔区域土壤CO_2脱气通量为2.054~7.877 kg/(m2·a),含喷气孔地区的土壤CO_2脱气通量是一般土壤脱气量的18.9倍;与全球火山区土壤脱气量(0.001~2.25 Mt/(m2·a))相比,其值显著偏低;但比青藏高原高寒草原生态系统土壤的CO_2排放量(187.46 g/(m2·a))大。结合区域地质背景推测地热系统中的CO_2含量主要来源于岩浆脱气和热液同长石等围岩矿物的蚀变反应。区内土壤CO_2的低脱气通量受透水性较差的碎屑岩沉积盖层约束。     

作用在裂隙中的渗透力分析

裂隙岩体中流体对岩体的作用力, 是研究岩体稳定性的重要问题。本文认为流体作用于裂隙壁面上的力包括两部分, 即垂直于裂隙壁面的流体静水压力 (导致裂隙垂向变形)和平行于裂隙壁面的拖曳力 (导致裂隙切向变形), 此拖曳力为面力。文中以单裂隙水流的立方定律为基础, 运用流体力学的动量方程, 推导出了单一平直光滑无充填裂隙、有充填的裂隙及水流和充填物一起运动情况下, 裂隙壁面承受的切向拖曳力公式。该公式对于分析流体对裂隙岩体变形性能及强度的影响具有重要价值。     

注入时间和静水压力对孔隙热储层中Cl-运移影响

迄今为止,注入时间和静水压力对溶质在深层承压地热水中的运移规律影响研究少有报道。通过模拟35℃的低温地热环境,开展了注入时间1,2,3,4,5 h以及静水压力0,6,9 MPa条件下Cl^-的运移柱模拟试验。采用CXTFIT 2.1软件进行数值模拟,探讨了孔隙型热储砂土中Cl^-的运移规律和影响因素。结果表明：在模拟的低温孔隙型热储层中,不同注入时间和静水压力下,Cl^-的运移曲线均呈正态对称分布,一维对流弥散(CDE)模型也可较好地表征其穿透曲线,因此溶质扩散过程符合菲克定律。注入时间的不同,会引起Cl^-的穿透曲线、运移参数发生变化,这与不同注入时间条件下溶质注入总量、柱内溶质浓度差以及分子扩散能力不同有关。在不同静水压力条件下,弥散系数从0 MPa的25.22 cm²/h增加到9MPa的36.13 cm²/h,分子扩散系数、机械弥散系数以及弥散度也随之增大,因此溶质的弥散作用随静水压力的增大而增强。研究结果对于丰富地下水的溶质运移理论具有重要意义。     

Analysis of Blast Wave Interaction with a Rock Joint

The interaction between rock joints and blast waves is crucial in rock engineering when rock mass is suffered from artificial or accidental explosions, bursts or weapon attacks. Based on the conservation of momentum at the wave fronts and the displacement discontinuity method, quantitative analysis for the interaction between obliquely incident P- or S-blast wave and a linear elastic rock joint is carried out in the present study, so as to deduce a wave propagation equation. For some special cases, such as normal or tangential incidence, rigid or weak joint, the analytical solution of the stress wave interaction with a rock joint is obtained by simplifying the wave propagation equation. By verification, it is found that the transmission and reflection coefficients from the wave propagation equation agree very well with the existing results. Parametric studies are then conducted to evaluate the effects of the joint stiffness and incident waves on wave transmission and reflection. The wave propagation equation derived in the present study can be straightforwardly extended for different incident waveforms and nonlinear rock joints to calculate the transmitted and reflected waves without mathematical methods such as the Fourier and inverse Fourier transforms.     

Analytical solution to axisymmetric consolidation of unsaturated soil stratum under equal strain condition incorporating smear effects

This paper proposes closed‐form analytical solutions to the axisymmetric consolidation of an unsaturated soil stratum using the equal strain hypothesis. Following the 1‐dimensional (1D) consolidation theory for unsaturated soil mechanics, polar governing equations describing the air and water flows are first presented on the basis of Fick's law and Darcy's law, respectively. The current study takes into account the peripheral smear caused by an installation of vertical drain. Separation of variables and Laplace transformation are mainly adopted in the analytical derivation to obtain final solutions. Then, the hydraulic conductivity ratio, the radius of influence zone and smear parameters influencing time‐dependent excess pore pressures, and the average degree of consolidation are graphically interpreted. In this study, a comparison made between the proposed equal strain results and the existing free strain results suggests that both hypotheses would deliver similar predictions. Moreover, it is found that the smear zone resulting from vertical drain installations would hinder the consolidation rate considerably.     

砂土的流体动力学方程与本构模型的比较

目前砂土材料连续力学方程建模有两种途径,一种是源自于论证Navier-Stokes方程时所用的方法,称为流体动力学方法,主要针对普通固体、普通流体、超流、液晶、高聚物、颗粒物质等材料,它的基本做法是先给出守恒变量（如能量、动量、熵等）和对称破缺变量（如弹性应变、量子相位等）的一般运动方程,再用与具体材料有关的热力学函数和迁移系数来封闭它们;另一种方法是本构模型法,针对有塑性固体、非牛顿流体、砂土材料等材料,该做法特点是直接构建应力、应变、应力率、应变率、速度、密度、温度等变量之间的函数关系,并以此来封闭连续和牛顿方程。近年来采用这两种方法建立的砂土方程在文献上都有报道,因此,有必要对两者的特色、科学基础、适用范围,包括概念上的和具体方程等,进行比较,作为颗粒物理与土力学之间跨学科交流的一种尝试和沟通。通过比较得出,两种建模途径对表征砂土状态的完备变量集、屈服面、与塑性有关的耗散等使用了很不一样的思路和方程。