Approaches for modeling longitudinal dispersion in pore-networks

The purpose of this study is to quantify the dispersivity in the longitudinal direction by upscaling pore scale mixing over a network domain and to verify the dispersivity with that obtained through the more rigorous upscaling technique, the Brownian particle tracking model (BPTM). We model a porous medium with a network of pore-units that are comprised of pore bodies and bonds of finite volume. Such a pore-unit is assumed to be a mixing cell with the steady state flow condition for a single fluid. Dispersivity can be obtained by solving the mixing cell model (MCM) for the concentration in each pore-unit and by averaging the concentrations for a large number of pore units (as a function of time and space). A minimal size of network that ascertains an asymptotic value of dispersivity was determined and verified with large size pore networks. This numerically computed dispersivity is compared with the results from the BPTM for the same porous medium and flow conditions. We show that the dispersivity obtained from the MCM is equally reliable for the heterogeneous pore-networks and can be estimated as a function of pore size heterogeneity. For homogeneous networks with the MCM, the iteration time step plays an important role. On the other hand, for networks with the BPTM, the assumption of intra-bond velocity profile affects the results.     

The monosaccharide spectra of natural waters

Monosaccharides were determined in waters and sediment pore waters from a wide variety of environments and locations. Desalting was performed by electrodialysis and concentrated extracts were analyzed by two forms of liquid chromatography. At least 12 sugars were identified. Glucose and fructose were the dominant monosaccharides in nearly all samples examined. Analyses of over 150 seawater and sediment pore water samples showed that fructose is highly significantly correlated (>0.99) with glucose concentrations. Laboratory kinetic experiments on the epimerization reaction, glucose ? fructose, in sterilized natural seawater in the dark, yielded a forward rate constant, k₁, of 1.2 × 10^?5 h^?1 at 25°C and 1.6 × 10^?7 h^?1 at 2°C. The approximate time required to attain equilibrium at 25°C was 1.1 y and at 2°C, 15.4 y; the measured equilibrium constant was in the range 0.3–0.4. The actual ratio of fructose to glucose in natural water samples was usually in the range 1.0–1.4/l, independent of the total monosaccharide concentrations, which varied in the samples by a factor of ～100. Several possible explanations for the apparent discrepancy in the determined and found ratios are discussed: the presence of universal, as yet, undiscovered major biological sources for fructose in marine environments; preferential utilization of glucose; preferential incorporation of fructose into or onto inorganic colloids; and preferential formation of fructose-transition metal ion associations.     

基于线要素动态化简的匹配算法比较与评价

矢量线要素数据来源多样,细节层次不一,限制了已有匹配算法正确率的提高,同时也给算法评价带来困难。化简可以减少线要素细节层次,提取其主要形态,据此提出一种基于线要素动态化简的匹配算法评价新方法。对不同匹配算法采用相同数据,在相同化简算法支撑下进行匹配,从而实现对不同匹配算法的评价。首先,阐述动态化简方法提取线要素主要形态的过程;其次,利用动态化简分别辅助4种已有匹配算法,获取每个匹配算法的最优匹配正确率;最后,将4种匹配算法的原始匹配结果与加入动态化简后的匹配结果进行对比,分析化简对匹配结果的影响,并把该影响运用到匹配算法的比较和评价中来。其中,1通过匹配正确率变化、误匹配等分析了匹配算法的数据适用性;2通过化简比例系数K变化时新增匹配数量的统计,评价了匹配算法对线要素局部细节的敏感程度并提出该指标的量化方法;3结合匹配算法采用的匹配相似度指标对其作出评价。     

2000～2015年会理县地表覆盖变化监测

以LandSat多时相影像为数据源,采用基于规则的面向对象分类方法,监测会理县2000～ 2015年地表覆盖变化.结合1∶50 000 DEM数据,分析了会理县地表覆盖构成与转移、变化动态度及潜在退耕地情况.监测分析结论能为会理县加强空间管制、促进土地资源集约利用、指导生态文明建设等提供决策信息支撑.     

高海拔隧道涌突水预测分析——以四川小卡子隧道为例

小卡子隧道是连接九龙县城和石棉县城的一条便利通道,它是连接S215和S211的绿色保障,九龙和石棉之间是海拔高度4 000 m以上,九龙县城周边为高原宽谷丘陵地区,地势起伏较大。九龙至周边沿线不良地质和特殊褶皱构造发育,其中冰雪害几乎每年冬春都发生,且影响线路较长,其它地质灾害也时常暴发,致使交通事故频繁发生,成为制约九龙县发展,因而急需要对线路进行改造,拟建连接九龙县至石棉县小卡子隧道即为公路改建工程。     

考虑桩-土体系渐进破坏的单桩承载特性研究

针对目前桩基承载特性确定时未考虑桩-土体系渐进变形过程的现状,采用现场试验和理论分析等手段对考虑桩-土体系渐进破坏的单桩承载特性展开研究。首先,利用现场试验数据对侧阻和端阻的软化特性展开深入探讨,提出了侧阻和端阻软化模型,明确了模型中各参数取值方法,并验证了其合理性。同时,根据提出的侧阻和端阻软化模型,建立了一种可考虑桩-土体系渐进破坏的单桩承载特性的迭代算法。算例分析表明,计算获得的破坏性单桩承载特性与实测值有较好的一致性,且可反映侧阻和端阻的破坏特性。实际工程中,结合单桩承载特性分析算法,可根据单桩的实际受力特点灵活选用不同形式的侧阻和端阻荷载传递函数来分析不同桩顶荷载水平下的单桩受力特性。     

高压旋喷双液分喷法在高层建筑地基加固中的应用

广东花都市新世纪大厦是一座29层的四星级宾馆，其场地素填土、第四系冲积层分散、基岩溶沟、溶槽发育，第四系孔隙水与基岩岩溶裂隙水通过导水天窗发生水力联系。大厦地基处理工程是项大型的复杂岩土工程，采用高压（30－38MPa）旋 喷双液分喷法处理后，对施工的2653根桩进行了雷达扫描，检测结果桩身质量良好，桩体分布均匀；抽样291根桩的小应变检测亦表明，桩身完整，桩体密度、单桩与桩土复合地基的允许承载力均达到或超过设计要求；35个点的19次沉降观测，大厦基础9个月累计沉降0．965－0．892mm，符合规范要求；设计方和建设方对大厦地基加固工程给予了较高的评价。     

Changing power relations in the WTO – Why the India–U.S. trade agreement should make us worry more,rather than less,about global trade governance

This review offers a critical reading of the November 2014 India–U.S. trade deal that unblocked an impasse in the World Trade Organization’s (WTO) Doha round and considers what it means for the way we govern global trade. It argues that the agreement, rather than being a ‘victory’ for the developing world or a cause for celebration, may simply reinforce an unfair and problematic system of distributing trade opportunities among WTO members. It may also obscure further the need for a fundamental overhaul of the way global trade is governed. In so doing, the review speaks to broader debates about what happens when ‘rising’ powers replace established states in global institutions in the absence of wider processes of reform; and it adds to growing concerns about the increasing precariousness of least developed countries (LDCs) in international economic regimes.     

Applied geophysics for cover thickness mapping in the southern Thomson Orogen

Abstract

Potentially mineralised Paleozoic basement rocks in the southern Thomson Orogen region of southern Queensland and northern New South Wales are covered by varying thicknesses of Mesozoic to Cenozoic sediments. To assess cover thickness and methods for estimating depth to basement, we collected new airborne electromagnetic (AEM), seismic refraction, seismic reflection and audio-frequency magnetotelluric data and combined these with new depth to magnetic basement models from airborne magnetic line data and ground gravity data along selected transects. The results of these investigations over two borehole sites, GSQ Eulo 1 and GSQ Eulo 2, show that cover thickness can be reliably assessed to within the confidence limits of the various techniques, but that caveats exist regarding the application of each of the disciplines. These techniques are part of a rapid-deployment explorers’ toolbox of geophysical techniques that have been tested at two sites in Australia, the Stavely region of western Victoria, and now the southern Thomson Orogen in northern New South Wales and southern Queensland. The results shown here demonstrate that AEM and ground geophysics, and to a lesser extent depth to magnetic source modelling, can produce reliable results when applied to the common exploration problem of determining cover thickness. The results demonstrate that portable seismic systems, designed for geotechnical site investigations, are capable of imaging basement below 300 m of unlithified Eromanga Basin cover as refraction and reflection data. The results of all methods provide much information about the nature of the basement–cover interface and basement at borehole sites in the southern Thomson Orogen, in that the basement is usually weathered, the interface has paleotopography, and it can be recognised by its density, natural gamma, magnetic susceptibility and electrical conductivity contrasts.     

余震作用下堰塞坝体破坏及溃决过程大型振动台试验研究

山区特大地震往往导致大量堰塞湖,例如2008年汶川地震形成了至少257个堰塞湖,并且主震后发生了大量余震,这些余震可能会影响堰塞坝体的安全状态。通过大型振动台模型试验,研究了余震及库水耦合作用下堰塞坝体的破坏及溃决机理和过程。共进行了两组不同材料的振动台模型试验,分别模拟含黏粒较多且颗粒较小（坝体Ⅰ）和基本不含黏粒且颗粒较大（坝体Ⅱ）的两种坝体。在不同水位条件下进行振动台试验。研究成果表明：（1）地震和库水耦合作用下堰塞坝体的主要溃决方式是漫顶溢流,主要溃决过程为地震力使松散的堰塞坝体发生沉陷,库水渗入使沉陷加剧,最终水位上升漫过坝顶发生溢流冲蚀破坏。（2）地震一般不会直接引起堰塞坝体的破坏。地震力对坝体稳定性的主要影响是使坝体发生沉陷变形。在地震和库水耦合作用下,坝体沉陷比单一因素作用下更为剧烈,因此地震作用会使漫顶溢流提前发生。（3）地震和库水耦合作用下坝体Ⅰ沉陷量大于坝体Ⅱ,说明现实中由大粒径岩土体组成的堰塞坝体具有更好的稳定性。