复合衬垫土工膜褶皱网络水力连通性分析方法

褶皱的水力连通长度是复合褶皱渗漏量评估的关键参数,褶皱网络的水力连通性分析还缺乏客观高效的分析方法。基于对漏洞周围水头分布的简化,提出以搜索长度为标准判定褶皱间水力连通性。通过将褶皱线段化,建立了褶皱网络连通性数字化分析方法,并编制了相应的分析程序,研究了该方法在文献报道的褶皱网络和处于良好状态的GM/GCL（土工膜/土工复合膨润土垫）衬垫中的应用。结果表明：搜索长度的定义给出了判定褶皱间水力连通性的客观标准,能反映衬垫的不同参数（如水头、界面导水系数以及渗透系数等）对褶皱间水力连通性的影响。褶皱线段化使褶皱位置和尺寸的描述更容易,数字化的水力连通分析简便且高效。基于该水力连通性分析方法的渗漏量评估结果偏保守。在进行渗漏量计算时,若假定统一的长度来描述褶皱网络,则需要根据漏洞频率的不同选择不同值。该水力连通性分析方法作为渗漏量评估完全数字化的关键环节,具有重要的应用前景。     

有机污染物在复合衬垫中的运移分析

有机污染物在垃圾填埋场复合衬垫中有两种不同的运移方式:土工膜上缺陷处污染物的运移和完好复合衬垫中污染物的扩散。文章分别用有限差分法和解析法对两种方式下污染物的累积量进行计算,分析了两种方式对有机污染物运移所做的贡献。研究表明:GCL(人工合成材料粘土衬垫)复合衬垫以有机污染物在完好复合衬垫中的扩散为主,可以忽略缺陷处污染物的运移;而CCL(压实黏土衬垫)复合衬垫中两种运移方式所做的贡献在同一数量级,需要考虑两种方式的共同作用。在GCL复合衬垫下铺设粘土层能有效改善GCL复合衬垫对有机污染物的阻止效果。     

Development of a technique for modelling clay liner desiccation

This paper presents a model for the analysis of clay liner desiccation in a landfill barrier system due to temperature effects. The model incorporates consideration of fully coupled heat‐moisture‐air flow, a non‐linear constitutive relationship, the dependence of void ratio and volumetric water content on stress, capillary pressure and temperature, and the effect of mechanical deformation on all governing equations. Mass conservative numerical schemes are proposed to improve the accuracy of the finite element solution to the governing equations. The application of the model is then demonstrated by examining three test problems, including isothermal infiltration, heat conduction and non‐isothermal water and heat transport. Comparisons are made with results from literature, and good agreement is observed. Copyright © 2003 John Wiley & Sons, Ltd.     

Determinants of poverty: lessons from Kenya

Poverty and food security are twin concerns of Kenya in a manner similar to many affected developing countries. It is characterized by the inability of the affected households in the country to acquire and retain sustainable livelihoods. The picture in Kenya is bound to be complicated by the projected changes in climate, as well as by population increase and environmental degradation, all which will put pressure on the natural resource base and militate against the achievement of sustainable development. The poverty picture in Kenya has hardly changed since independence over four decades ago despite the enormous resources and efforts which have been directed at tackling it. The current national poverty level remains high at well over 70% in some pockets which remain particularly vulnerable. Following the recent post-election violence, there is now a fear that the situation could degenerate into famine conditions and further hopelessness for a sizeable proportion of the rural population. Government efforts to eradicate poverty and food insecurity spelled out in a thirty year development plan are unlikely to succeed unless underlying causes of inequality are properly addressed. The paper contains suggestions for new approaches to addressing the twin problems.     

加肋土工膜衬垫系统稳定性分析

针对填埋场衬垫系统薄弱界面容易失稳,在加肋土工膜与砂土界面力学机制分析的基础上,改进了传统双楔体分析法,考虑了加肋土工膜肋块端部端承阻力对衬垫系统稳定性的影响,建立了加肋土工膜衬垫系统稳定性分析解析解。结合某实际工程初步设计,对加肋土工膜衬垫系统进行了稳定性分析,探讨了肋块形状、肋块高度和加肋间距对衬垫系统安全系数的影响。分析结果表明,该解析解能更好地计算加肋土工膜衬垫系统的安全系数。当加肋间距为20 mm时,肋块高度对安全系数的影响较大;当肋块高度一定时,安全系数随着加肋间距增加而逐渐减小;在加肋间距大于200 mm之后,加肋土工膜已接近光面土工膜的剪切特性。     

饱和土中任意形状衬砌对稳态压缩波的散射

采用不同的复平面间的保角映射法,对无限饱和土中任意形状的多孔衬砌结构对弹性压缩波的散射问题进行了研究。首先,通过引入位移势函数将饱和土和衬砌两种介质的Biot波动方程解耦成6个Helmholtz方程,并求出复平面极坐标下相应势函数的通解;之后,利用两个复平面间的极角变换关系,得到位移、应力和孔压在映像平面上势函数表达式。在此基础上,将原像平面中任意形状的衬砌内外边界处的边界条件代入到映像平面中圆环势函数的关系式中,从而求出饱和土中衬砌介质在弹性稳态体波作用下产生的动态响应。最后通过具体算例,变换不同的入射角及介质参数得出相应数值解及规律。     

Fracture in a heterogeneous medium: a network approach

Fracture in a heterogeneous medium is simulated by a network model. Heterogeneity is introduced by randomly distributing an initial population of cracks on a triangular network of bonds. Each ruptured bond represents a crack. External stresses are applied onto the network and the evolution of the crack population is analysed when the stresses are increased. A crack will propagate to an intact bond if the critical crack extension force is reached. This propagation leads to the coalescence of bonds: crack clusters are formed. When their shapes are complex we approximate them by simpler ones to compute a crack extension force. Crack interactions are introduced by adding for a given bond the contributions of all adjacent dusters. By using this kind of approach combining fracture mechanics and network modelling, we are able to simulate the rupture of a rock specimen under compression/ traction or shear stresses and to give some characteristics of the macroscopic fracture.     

Physical simulation and application of a new TEM configuration

In some applications, especially for tunnel surveys and ancient tomb investigations, the scale of survey location is so small that it is impossible to lay a large enough transmitter loop for detection. A small-scale and high-power Transient Electromagnetic (TEM) transmitter configuration must be adapted to detect longer distance or greater depth. Redesigning the TEM surveying configuration may facilitate improving signal penetration and precision of TEM soundings. Based on physical simulation, a newly designed special-loop-source TEM survey configuration has been introduced, which employs four square apertures within a single large transmitter loop to excite stronger fields. The primary and secondary fields have been measured using both the new special-loop system and standard normal single loop TEM configuration for different receiver-transmitter separations and for different target depths. The response curves were compared, revealing that the primary field intensity and the secondary field response were improved by the special-loop transmitter system as compared to the standard system. The new special-loop configuration can be used for tunnel TEM prediction and other TEM investigations. A case study was conducted on tunnel forecasting in Hubei Province, China. This terra TEM survey showed that it is an effective and successful method for exploring and predicting challenging geological structures ahead of a tunnel wall during excavation.     

膨润土改性黄土衬里防渗性能室内测试与预测

试验测定了膨润土改性黄土试样的渗透系数,研究膨润土改性黄土用作废弃物填埋场衬里的可行性,为天然黏土匮乏地区防渗材料本土化提供依据。选取两种代表性黄土,即黏性较大的兰州黄土(LH)和砂性较大的榆林黄土(YH),分别向其中添加不同比例的两种膨润土后击实成样,利用柔性壁渗透仪测定改性黄土的渗透系数,分析了改性黄土渗透系数随膨润土添加率增大的变化规律,确定了满足衬里防渗要求的膨润土添加率。利用扫描电镜照片统计了改性黄土的孔隙特征参数,发现添加膨润土后黄土中原有的大孔隙被充填或分隔成更多的中、小孔隙,有效阻滞了渗流液体通过,从微观结构的角度揭示了改性黄土渗透性降低的实质。依据实测数据建立了膨润土改性黄土的渗透回归模型,据此可以预测不同添加量的膨润土改性黄土的渗透系数。     

GCL与CCL复合衬垫的等效性分析

土工合成材料粘土衬垫(GCL)与土工膜(GM)形成的复合衬垫在垃圾填埋场中的应用日益广泛.我国规范中允许在特殊情况下用GCL代替压实粘土(CCL)做垃圾填埋场的衬垫,但是对于"特殊情况"没有明确说明.本文采用数值方法对复合衬垫中无机污染物的对流和扩散进行了计算,从衬垫底部污染物通量和累积量两个角度对GCL复合衬垫和CCL复合衬垫阻滞污染物运移的效果进行了比较,分析两种复合衬垫的等效性,并研究了GCL复合衬垫的适用范围.结果表明,当渗滤液水头较高时,GCL复合衬垫体现出其优势.     

Determinants of migration decision-making for rural households: a case study in Chongqing,China

Migration is a global strategy for promoting economic growth and sustainable urbanization, specifically in developing countries. It is critical for governments to understand the determinants of migration decision for rural households so that proper migration measures can be taken. Different from previous studies that mainly focus on migration determinants without considering migration patterns, this paper divides migration patterns into three types—no migration, labor migration, and family migration, and examines the determinants for “no migration–migration” and “labor migration–family migration,” respectively. The binary logistic model is adopted to analyze the impacts of various migration factors in Chongqing city. Results show that: (1) per capita non-agricultural income plays the most significant positive role in driving “no migration–migration.” This is followed by the number of household labor force, whereas road accessibility is the key factor for inhibiting migration. (2) The key contributory factor for “labor migration–family migration” is per capita non-agricultural income. This is followed by the residential distance from towns, whereas the number of household labor force and the average age of labor force are restraining factors. The research results can effectively provide scientific reference for local governments to advance the transfer of the surplus rural labor force to promote sustainable urbanization.

     

有机污染物在完好复合衬垫中的迁移分析

在复合衬垫中,有机污染物除了在土工膜缺陷处发生迁移外,在完好土工膜中的迁移也是主要方式。考虑有机污染物在土工膜边界处的浓度跳跃现象,建立了有机污染物在完好复合衬垫中迁移的一维模型,得到了解析解。通过与有限差分解的比较,验证了解答的合理性。应用该解答分析了GCL复合衬垫和CCL复合衬垫防止有机污染物渗漏的效果。结果表明,CCL复合衬垫的效果较好,可以通过黏土改性和增加黏土厚度的方法来提高其有效性。有机污染物类型的选择对GCL复合衬垫的分析结果影响较大,而阻滞系数的变化对分析结果影响较小。     

Characterization of geosynthetic clay liner bentonite using micro-analytical methods

In barrier design, familiarity of the structure and composition of the soil material at the micron scale is necessary for delineating the retention mechanisms of introduced metals, such as the formation of new mineral phases. In this study, the mineralogical and chemical makeup of the bentonite from a geosynthetic clay liner (GCL) was extensively characterized using a combination of conventional benchtop X-ray diffraction (XRD) and micro X-ray diffraction (μXRD) with synchrotron-generated micro X-ray fluorescence (μXRF) elemental mapping and μXRD (S-μXRD). These methods allow for the non-destructive, in situ investigation of a sample, with μm spatial resolution. Synchrotron-based hard X-ray microprobes are specifically advantageous to the study of trace metals due to higher spatial resolution (<10 μm) and higher analytical sensitivity (femtogram detection) than is possible using normal laboratory-based instruments. Minerals comprising less than 5% of the total bentonite sample such as gypsum, goethite and pyrite were identified that were not accessible by other conventional methods for the same GCL bentonite. Two dimensional General Area Diffraction Detector System (GADDS) images proved to be particularly advantageous in differentiating between the microcrystalline clay, which appeared as homogeneous Debye rings, and the ‘spotty’ or ‘grainy’ appearance of primary, more-coarsely-crystalline, accessory minerals. For S-μXRD, the tunability of the synchrotron X-rays allowed for efficient distinction of both clay minerals at low scattering angles and in identifying varying Fe oxide minerals at higher angles. GCL samples permeated with metal-bearing mining solutions were also examined in order to consider how mechanisms of metal attenuation may be identified using the same techniques. In addition to the cation exchange capacity from the montmorillonite clay, tests showed how minerals comprising only 1–2% of the bentonite such as goethite could potentially play a significant role in sequestering a range of metals, specifically Ni, Zn and Cu.     

Irrigation in sub-humid environments: a comparison of three cultures

The use of irrigation to intensify crop production is widespread. Superficial morphological, administrative, and socio-economic similarities between sites separated by time, space and culture prompted an analysis of three cultural groups in similar geographical settings to determine the extent of cross-cultural similarities in irrigation practice. The groups analyzed were Mormon settlements in the Wasatch Mountains of the United States, and Jewish and Arab settlements in the Jordan Valley of Israel and Jordan. Analysis of irrigation use among the three groups revealed marked similarities in organizational, administrative and technological practices. In each case, irrigation practice has progressed from simple community-based diversion to large-scale diversion schemes as population and political organization increased. Minor differences concerning ownership of water rights were the only notable exceptions to the broad similarity between the groups. In terms of water development practice, each group progressed through essentially similar stages, reflecting the level of water demand in each society. We hypothesize on the basis of the examination of the study groups that irrigation-based societies progress through a sequence of irrigation practices, from Stage 1 (simple diversion) to Stage 5 (societal-wide adoption of laws and projects to maximize efficiency of water use), as population growth intensifies demand on limited water resources in sub-humid environments.     

Characterization of locally available soil as a liner material for solid waste landfills in Sri Lanka

This study aimed to develop a low-cost and effective clay liner material for solid waste landfills in Sri Lanka. A locally available clayey soil and its admixtures with 5 and 10% bentonite were examined for this purpose. Laboratory experiments to determine soil plasticity and swell index were carried out on the tested samples. Hydraulic conductivity (k) tests were carried out in the laboratory using water and an aqueous solution of CaCl₂ on unconsolidated samples prepared by either dry or slurry packing and pre-consolidated samples with five different consolidation pressures (p) from 10 to 200 kPa. Measured liquid limits for tested admixtures increased with increasing bentonite contents and correlated well with measured values of the swell index. The difference in permeant solutions had little effect on measured k values for both unconsolidated and pre-consolidated samples. The hydraulic conductivities were highly affected by changing p, i.e., the k values decreased on two orders of magnitude as p increased from 10 to 200 kPa. The Kozeny–Carman equation, a theoretical permeability model that expresses the k-porosity relationship, was applied to measured data including reported values. Results showed the Kozeny–Carman equation captured well the porosity-dependent k values for tested soils and their admixtures with bentonite under a wide range of void ratios, suggesting that the Kozeny–Carman equation is a useful tool to estimate the magnitude of k values for differently compacted soil and its bentonite admixtures.     

Analysis of biological clogging potential in a simulated compacted clay liner subjected to high-strength leachate infiltration

A bench scale study was conducted to assess the possibility and extent of biological clogging in compacted clayey soil exposed to high-strength leachate simulating conditions in a landfill. In two series of experiments, distilled–deionized water, slightly acidic water and fresh high-strength leachate were permeated through compacted clayey soil and the rate of infiltration was recorded. Colony-forming units per unit mass of soil were counted, and scanning electron microscope photographs were taken before and after termination of experiments. Results indicated that infiltration of leachate containing a very high concentration of organic matter followed a logistic fit indicating hydraulic clogging of the porous media. This was in agreement with a five order of magnitude greater bacterial growth compared to the original state of the soil and to cases where distilled–deionized and acidified water was used as the permeant. Water and acidified water infiltration followed a power fit indicating persistent infiltration through the end of experiments with no sign of clogging. Bacterial counts in these cases were similar to that of the original state of the soil. Photographs taken by scanning electron microscope also indicated formation of plate-like material within the soil texture in contrast to no change when water was used as the permeating fluid and to formation of holes when acidified water was infiltrated through the soil. It was concluded that biological clogging considerably reduced the rate of infiltration within compacted clayey soil shortly after exposure to high-strength leachate.     

Seismic velocity structure and gravity anomalies: a comparison

The question was examined as to whether the same gravity anomaly is produced for a range of crustal velocity structures all of which produce similar seismic record sections. The results indicate that the maximum errors in the computed gravity anomalies for the various velocity structures is around 20–30 mGal for some models and is around 50 mGal for many others. A major source of error is underestimating the effect of a seismic low-velocity zone which is at one end of the correct velocity structure and which was not detected by several of the interpretations presented at a recent workshop. If no low-velocity layer is included, the error in the gravity anomaly is 30 mGal. The choice of a particular velocity-density relationship does not seem to be a serious problem in the analysis, except for the case of the low-velocity zone, as long as we use a continuous velocity-density curve.