水膜理论在非饱和土中吸力的应用研究

非饱和土中总吸力问题一直是非饱和土土力学研究的一个重要分支。本文引用并引伸了水膜理论,把水膜理论的水膜范围扩展到包括结合水和毛细作用及基质吸力等引起的自由水（重力水）等部分,相应的水膜分离压也包括基质吸力和毛细作用,因此,非饱和土中的总吸力相应地可表示为扩展后的水膜分离压。从广义水膜理论及土性方面分析非饱和土总吸力,探讨了非饱和土中水膜对总吸力的影响,导出了广义非饱和土水膜理论下的总吸力公式,给出了非饱和土总吸力当土颗粒大小不同时与饱和度的关系。理论计算与试验结果吻合较好,表明了广义水膜理论对研究非饱和土总吸力具有一定的指导意义。     

Effects of surfactant adsorption and surface forces on thinning and rupture of foam liquid films

The properties of thin liquid films (TLF) are of paramount significance for colloidal disperse systems, and a number of industrial processes, including froth flotation. In flotation, the bubble–particle attachment is controlled by the thinning and rupture of the intervening liquid film between an air bubble and a mineral particle. The froth evolution and its transient stability are also a function of the drainage and rupture of liquid films between air bubbles. Surface-active substances (surfactants) are used as flotation reagents to control the behavior of the liquid films. This paper presents a review of our research in the area of surfactant adsorption, surface forces and liquid films. It mainly focuses on the validation, application and extension of the Stefan–Reynolds theory on the liquid drainage. The extension of the Stefan–Reynolds theory comprises surface forces (disjoining pressure), surface tension variation, caused by the adsorption and diffusion of surfactants. Both the experimental and theoretical results are mostly related to the free (foam) films formed between two bubbles but can be principally extended to emulsion films between two oil drops and wetting films between an air bubble and a solid surface.     

Aeration characteristics of laboratory flotation machine impellers

The aeration characteristics of several laboratory flotation machine impellers have been studied paying special attention to the pressure generated by impeller rotation. Correlations have been established between pressure (or Euler) number and Reynolds number, pressure ratio and air flow number, and these correlations have been compared with the conventional power correlations. Aeration and addition of frother affect both the power and the pressure generated by the rotating impeller; both decrease with increasing frother concentration, although in the low-impeller-speed region at relatively high frother concentrations the decrease in pressure is more pronounced than the decrease in power. Possible applications are mentioned and suggestions for further work are made.     

Effect of humidity on dynamic foam stability

It is experimentally shown that the stability of non-overflowing pneumatic foams, such as those used in the Bikerman foam stability test, is strongly dependent upon the gradient of humidity within the freeboard of the column. Growing foams can be prevented from exhibiting collapse, even at surfactant concentrations significantly lower than the critical micelle concentration, by saturating the air above the foam surface thereby preventing liquid evaporation. These observations have important implications for the performance of flotation devices, as well as instruments designed to measure the stability of aqueous foams. Meteorological data for two mining sites in Australia throughout a single year shows the variability of humidity, and therefore stability, of flotation froths.     

Interaction of calcium dioleate collector colloids with calcite and fluorite surfaces as revealed by AFM force measurements and molecular dynamics simulation

Spherical calcium dioleate particles (∼ 10 μm in diameter) were used as AFM (atomic force microscope) probes to measure interaction forces of the collector colloid with calcite and fluorite surfaces. The attractive AFM force between the calcium dioleate sphere and the fluorite surface is strong and has a longer range than the DLVO (Derjaguin–Landau–Verwey–Overbeek) prediction. The repulsive AFM force between the calcium dioleate sphere and the fluorite surface does not agree with the DLVO prediction. Consideration of non-DLVO forces, including the attractive hydrophobic force, was necessary to explain the experimental results. The non-DLVO interactions considered were justified by the different interfacial water structures at fluorite– and calcite–water interfaces as revealed by the numerical computation experiments using molecular dynamics simulation. The density of interfacial water at the fluorite surface is low and the fluorite surface is not strongly wetted by water molecules. In contrast to the water at the fluorite surface, water molecules at the calcite surface form tightly packed monolayer structures and the calcite surface is extensively hydrated by water molecules. The interfacial water structure agrees with the AFM force measurements and the flotation recovery data. The strong attraction between the calcium dioleate colloid and the fluorite surface, and the moderately wetted fluorite surface by water molecules explain the better flotation response of fluorite with the oleate collector colloid.     

基坑降水中渗流破坏归类及抗突涌验算公式评价

基坑降水工程中的渗流引发一种体积力即渗流力,尤其当坑底下覆承压含水层时可能引发以下渗流破坏现象如流砂、管涌、坑底突涌安全等,需要进行安全验算。以力的性质将安全验算分为2种判别标准：一种为面积力安全验算,另一种为体积力安全验算。对于抗突涌安全验算公式,在目前规范公式的基础上考虑了被浮托土块侧面抗剪强度安全储备的发挥,并结合天津市区内典型地铁车站基坑几何性状和取值极为保守的土性参数进行验算,结果表明抗剪强度可发挥至少1/4以上抗突涌贡献,对于基坑下呈透镜体状分布局部承压砂层,发挥作用更大。如考虑抗剪强度发挥减少井孔数量,既可节约工程费用,又可减少钻孔处的安全隐患。     

Shale gas fracturing using foam-based fracturing fluid: a review

World energy resources are depleting at an alarming rate, and natural gas has been identified as an environmentally friendly energy resource, with shale gas being one option. However, the extremely low permeability of shale plays has caused them to fail to produce a commercially viable amount of gas. Therefore, appropriate production enhancement techniques, including hydro-fracturing, are required. This paper reviews the research on shale gas production enhancement using foam-based hydro-fracturing and focuses on research on shale deposit distribution around the world, the importance of shale gas recovery, major shale gas recovery enhancement techniques, the effectiveness of foam-based fracturing depending on the foam type used and the formation properties, advantages and limitations of foam-based fracturing compared to other fluids, and existing experimental and numerical studies and field studies. According to the available experimental and modelling studies on foam fracturing, N₂-based foams are stronger than CO₂-based foams. The effective viscosity that controls the foam rheology decreases with increasing temperature and decreasing pressure and foam quality, and fracture length reduces and fracture width increases with increasing foam quality. Although this technique has been tested in few shale plays worldwide, most studies have been performed in the USA and Canada. Therefore, the foam fracturing technique is still comparatively novel for other countries around the world.     

Predominance of even carbon-numbered n-alkanes from lacustrine sediments in Linxia Basin,NE Tibetan Plateau: Implications for climate change

This study reports the first observation of predominant even C-numbered n-alkanes from sediments in the continuous lacustrine-sedimentary section (Maogou) from the Late Miocene to the Early Pliocene (13–4.4 Ma) in the Linxia Basin, NE Tibetan Plateau. The n-alkanes showed a bimodal distribution that is characterised by a centre at n-C₁₆–n-C₂₀ with maximum values at n-C₁₈ and n-C₂₇–n-C₃₁ as well as at n-C₂₉. The first mode shows a strong even C-number predominance (OEP_16–20 0.34–0.66). In contrast, the second mode has a strong odd C-number predominance (OEP_27–31 1.20–2.45). Certain types of special autochthonous bacteria are a possible source for this distribution of even C-numbered n-alkanes in lacustrine sediments. These bacteria may have a high production rate in weak oxic–anoxic and arid depositional environments, in which a variety of geochemical parameters have recorded palaeoclimate change.     

A case study on the behaviour of a deep excavation in sand

A complete case record of an excavation in sand is explored in this study. Numerical analyses were conducted to evaluate the influences of soil elasticity, creep and soil–wall interface. Back-analyses indicate small strain parameters should be used if an elastic–perfect plastic model is selected. In addition, excavation-induced seepage has only a limited effect on vertical displacements. Delayed installation of 3rd level struts and base slab construction caused significant time-dependent (creep) movements during the excavation. Back-analyses show that the dynamic viscosity (D_v) used in the visco-elastic model for creep simulation is in the range of 1.5 × 10¹⁵–2.0 × 10¹⁵ Pa, but there are still inconsistencies in movements both near to and far from the excavation. Interpreting from observation data, the creep rate of wall movement caused in the non-supported stage of the excavation varies between 0.14 and 0.38 mm/day. Finally, parametric studies of interface elements indicate that the most sensitive parameters are the normal (K_n) and shear stiffness (K_s) of the interface. Back-analyses using an elastic–perfect plastic model indicate that using 3 × 10⁶ Pa for K_n and K_s produces more acceptable results.     

Geochemical characterization of surface waters and groundwater resources in the Managua area (Nicaragua,Central America)

This paper reports new geochemical data on dissolved major and minor constituents in surface waters and ground waters collected in the Managua region (Nicaragua), and provides a preliminary characterization of the hydrogeochemical processes governing the natural water evolution in this area. The peculiar geological features of the study site, an active tectonic region (Nicaragua Depression) characterized by active volcanism and thermalism, combined with significant anthropogenic pressure, contribute to a complex evolution of water chemistry, which results from the simultaneous action of several geochemical processes such as evaporation, rock leaching, mixing with saline brines of natural or anthropogenic origin. The effect of active thermalism on both surface waters (e.g., saline volcanic lakes) and groundwaters, as a result of mixing with variable proportions of hyper-saline geothermal Na–Cl brines (e.g., Momotombo geothermal plant), accounts for the high salinities and high concentrations of many environmentally-relevant trace elements (As, B, Fe and Mn) in the waters. At the same time the active extensional tectonics of the Managua area favour the interaction with acidic, reduced thermal fluids, followed by extensive leaching of the host rock and the groundwater release of toxic metals (e.g., Ni, Cu). The significant pollution in the area, deriving principally from urban and industrial waste-water, probably also contributes to the aquatic cycling of many trace elements, which attain concentrations above the WHO recommended limits for the elements Ni (∼40 μg/l) and Cu (∼10 μg/l) limiting the potential utilisation of Lake Xolotlan for nearby Managua.     

The separate production of H2S from the thermal reaction of hydrocarbons with magnesium sulfate and sulfur: Implications for thermal sulfate reduction

The yields and stable C and H isotopic composition of gaseous products from the reactions of pure n-C₂₄ with (1) MgSO₄; and (2) elemental S in sealed Au-tubes at a series of temperatures over the range 220–600 °C were monitored to better resolve the reaction mechanisms. Hydrogen sulfide formation from thermochemical sulfate reduction (TSR) of n-C₂₄ with MgSO₄ was initiated at 431 °C, coincident with the evolution of C₂–C₅ hydrocarbons. Whereas the yields of H₂S increased progressively with pyrolysis temperature, the hydrocarbon yields decreased sharply above 490 °C due to subsequent S consumption. Ethane and propane were initially very ¹³C depleted, but became progressively heavier with pyrolysis temperature and were more ¹³C enriched than the values of a control treatment conducted on just n-C₂₄ above 475 °C. TSR of MgSO₄ also led to progressively higher concentrations of CO₂ showing relatively low δ¹³C values, possibly due to input of isotopically light CO₂ derived from gaseous hydrocarbon oxidation (e.g., more depleted CH₄).     

An induction time model for the attachment of an air bubble to a hydrophobic sphere in aqueous solutions

A phenomenological model is developed to describe the induction time of an air bubble in contact with a hydrophobic sphere, based on an analytical solution of Reynolds approximation under the specific boundary conditions. A modified version of induction time apparatus is used to measure the induction time of an air bubble with a methylated silica bead, an untreated silica bead in dodecylamine solutions and a bitumen droplet in alkaline solutions. It was found that the induction time between an air bubble and a silica bead (or a bitumen droplet) increased with increasing bubble size. The bubble size dependence is stronger for the large silica beads (or bitumen droplets) tested. The induction time, obtained from two different methylated silica beads diameters, is used to estimate the average net driving force (F̄_o) for the intervening liquid film drainage and rupture and the critical film thickness (h_c) in the established model. Through curve fitting, the values for F̄_o and h_c are found to be 3.5×10⁻⁸ N and 150 nm, respectively, for a methylated silica–bubble system. The predicted values of critical film thickness and the net driving force for the systems used in this study are in excellent agreement with those reported in the literature, confirming the present theoretical analysis and model development. The suitability of using the liquid drainage time to represent the induction time, or the attachment time, is experimentally justified.     

Effects of pressure on PbWO4-III

In a hydrostatic pressure environment condition and in manual milling, respectively, investigations of PbWO₄-III (P2₁ /n) have been performed by X-ray diffraction and Raman scattering techniques. Experiments found that PbWO₄-III keeps its monoclinic structure under hydrostatic pressures with the sample’s anisotropic compressibility up to 14.6 GPa, but transforms to PbWO₄-I (I4₁ /a) in a grinding process. The stability and variability of PbWO₄-III depending on the strain states were also explored by first-principles calculations of elasticity. Calculations show PbWO₄-III has an anisotropic compressibility and a ductile nature with increasing pressure up to 15 GPa.     

Use of biomarkers indices in a sediment core to evaluate potential pollution sources in a subtropical reservoir in Brazil

The presence of PAHs, n-alkanes, pristane, and phytanes in core sediment from the Vossoroca reservoir (Parana, southern Brazil) was investigated. The total concentration of the 16 PAHs varied from 15.5 to 1646 μg kg⁻¹. Naphthalene was present in all layers (3.34–74.0 μg kg⁻¹). The most abundant and dominant n-alkanes were n-C₁₅ and n-C₃₆, with average concentrations of 198.1 ± 46.8 and 522.9 ± 167.7 μg kg⁻¹, respectively. Lighter n-alkanes were distributed more evenly through the layers and showed less variation, specially n-C₉, n-C₁₂, and n-C₁₈, with average concentrations of 14.6 ± 3.0, 31.6 ± 1.9, and 95.0 ± 5.2 μg kg⁻¹, respectively; heavier n-alkanes were more unevenly distributed.     

Reusable nanocomposite-coated polyurethane foams for the remediation of oil spills

Cost-effective oil absorbents for the remediation of oil spills have been developed following a facile process involving the modification of polyurethane foam surfaces with mixtures of silicon oxide nanoparticles and polydimethylsiloxane. Polyurethane foams with different pore sizes and connectivity are tested, and it was found that the proposed treatment, applied by dip coating and spray coating, strongly improves the intrinsic foams’ performance in terms of selectivity and oil absorption capacity. The modified foams reach oil absorption capacities up to 60 g/g and simultaneous negligible water uptake. The treatment is stable after multiple absorption cycles, and therefore, the foams can be reused without significant decrease in their performance, being possible, after five cycles of absorption and recovery of oil, to reach overall oil absorption capacities up to 250 g/g.     

泡沫钻进流体循环用消泡器设计与数值模拟分析

高效、经济、环保的消泡技术是泡沫钻进流体循环利用的基础。根据气体引射器原理,设计了一种新型旋内喷式机械消泡装置,以压缩空气为动力介质,联合真空负压、冲击剪切、充气饱和及减速增压扩散4种作用方式快速消泡,实现泡沫流体的循环利用。利用计算流体动力学软件FLUENT对消泡器内部速度和压力流场进行了数值模拟分析,结果表明：旋内喷式消泡器内部产生两个相邻重叠的真空负压区域,能够对外界流体产生巨大的抽吸力,抽吸量是入口压缩空气质量流的1.6倍左右;当入口压缩空气的质量流为0.1 kg/s时,消泡器中心最大负压值达到了21 kPa;在交汇式喷射孔的多股射流交汇碰撞点附近,由于速度的提升,形成了一个更大的负压区域,对消泡产生积极作用。     

Characterization of the structure and the surface reactivity of a marcasite thin film

A thin film of marcasite, FeS₂, was synthesized under vacuum and its structure and reactivity under oxidizing conditions was investigated by means of diffraction and surface analytical techniques, respectively. Synthesis of the film was carried out by codepositing Fe and S₂ onto a Ta support. The thickness of the film could be varied from approximately 10 Å to 1 μm. High-resolution S 2p synchrotron-based photoemission showed S22−, with undetectable amounts of S²⁻ impurity that is typically present on natural sample surfaces. X-ray diffraction of the micron-thick films showed that the film crystallized in the marcasite phase of FeS₂. Atomic force microscopy indicated that the thin film had a nanometer-scale roughness suggesting the film contained defects such as steps and kinks. X-ray photoelectron spectroscopy studies found the thin marcasite film to be more reactive than natural pyrite (the most ubiquitous FeS₂ dimorph) after exposure to a gaseous O₂/H₂O environment on the basis of the amount of sulfate formation. Likely the oxidation of marcasite was dominated by its short-range order (e.g., presence of steps), because the density of nonstoichiometric defect sites (e.g., S²⁻) was low as assessed by photoelectron spectroscopy.     

A synthetic fluid inclusion study of copper solubility in hydrothermal brines from 525 to 725 °C and 0.3 to 1.7 GPa

Fluid inclusions were synthesized in a piston-cylinder apparatus under mineral-buffered conditions over a range of Cl concentration (0.29 to 11.3 mol kg⁻¹), temperature (525 to 725 °C), and pressure (0.3 to 1.7 GPa). All fluids were buffered by the mineral assemblage native copper + cuprite + talc + quartz. In situ fluid composition was determined by analysing individual fluid inclusions by LA-ICPMS and independently analysing the quench solution. The solubility data provide basic information necessary to model the high temperature behaviour of Cu in magmatic-hydrothermal systems. Copper concentrations up to ∼15 wt% were measured at 630 °C and 0.34 GPa. These results give an upper limit for Cu in natural fluids and support field-based observations of similar high Cu concentrations in fluids at near-magmatic conditions. Experimental evidence indicates that Cu⁺ may form neutral chloride complexes with the general stoichiometry with n up to 4, though n ? 2 is typical for the majority of the experimental conditions. At high pressure (>∼0.5 GPa) there is evidence that hydroxide species, e.g., CuOH⁰, become increasingly important and may predominate over copper(I)-chloride complexes. The roles of fluid mixing, cooling and decompression in ore-forming environments are also discussed.     

Comparison of arsenic geochemical evolution in the Datong Basin (Shanxi) and Hetao Basin (Inner Mongolia), China

Insightful knowledge of geochemical processes controlling As mobility is fundamental to understanding the occurrence of elevated As in groundwater. A comparative study of As geochemistry was conducted in the Datong Basin (Shanxi) and Hetao Basin (Inner Mongolia), two strongly As-enriched areas in China. The results show that As concentrations ranged from <1–1160 μg L⁻¹ (n = 37) in the Datong Basin and <1–804 μg L⁻¹ (n = 62) in the Hetao Basin. The groundwater is of the Na-HCO₃ type in the Datong Basin and Na-Cl-HCO₃ type in the Hetao Basin. Silicate mineral weathering and cation exchange processes dominated the groundwater geochemistry in the two study areas. Principal component analysis of 99 groundwater samples using 12 geochemical parameters indicated positive correlations between concentrations of As and Fe/Mn in the Datong Basin, but no correlation of As and Fe/Mn in the Hetao Basin. Phosphate correlated well with As in the Datong Basin and Hetao Basin, suggesting phosphate competition might be another process affecting As concentrations in groundwater. High concentrations of As, Fe, and Mn occurred in the pe range −2 to −4. The results of this study further understanding of the similarities and differences of As occurrence and mobility at various locations in China.     

The surface dilational viscosity of polypropylene glycol solutions and its influence on water flow and foam behavior

The non-equilibrium interfacial properties of a homologous series of aqueous polypropylene glycol solutions (400–2000 g/mol) were investigated as a function of concentration to understand their role in determining foam behavior. The overflowing cylinder technique was used to generate a continually expanding surface. Static and dynamic surface tensions, as well as the surface velocity of the expanding surface, were characterized. The surface dilational viscosity was compared to water flow rate and foam retention time of the polypropylene glycol solutions reported in the literature. This study suggests that the surface dilational viscosity is a key parameter in the Marangoni effect which retards water drainage, resulting in wetter foam and increased water recovery across flowing foams.