Application of Iron Nanoparticles Synthesized by Green Tea for the Removal of Hexavalent Chromium in Column Tests

Nano zero valent iron particles (nZVI) are popular the last few years because of the numerous applications in remediation of a wide range of pollutants in contaminated soils and aquifers. The nZVI particles can be 10 - 1000 times more reactive than granular or micro-scale ZVI particles due to the small particle size, large specific surface area and high reactivity. An alternative green synthesis procedure was used for the production of nano zero valent iron particles (nZVI) using green tea (GT) extract, which is characterized by its high antioxidant content. Polyphenols in green tea extract possess double role in the synthesis of nZVI, because they not only reduce ferric cations, but also protect nZVI from oxidation and agglomeration as capping agents. The objective of current study was to simulate ata laboratory scale the attachment of GT-nZVI particles on soil material and study the effectiveness of attached nanoparticles for removing hexavalent chromium (Cr(VI)) from contaminated groundwater flowing through the porous soil bed. Column tests were carried out with various flowrates in order to examine the effect of contact time between the attached on porous medium nZVI and the flow-through solution on Cr(VI) reduction. After the completion of column tests the soil material in each column was split in 5 vertical sections, which were further subjected to chemical analyses and leaching tests. According to the results of the study increasing the contact time favors the reduction and removal of Cr(VI) from the aqueous phase. The reductive precipitation of Cr can be described as a reaction that follows a pseudo-first order kinetic law, with rate constant equal to k = 0.0243 ± 0.0011 min-1. Leaching tests indicated that precipitated chromium is not soluble. In the examined soil material, the total amount of precipitated Cr was found to range between 280 and 890 mg/(kg soil), while soluble Cr was less than 1.4 mg/kg and most probably it was due to the presence of residual Cr(VI) solution in the porosity of soil.

Studies on parallel seismic testing for integrity of cemented soil columns

The principle and process of parallel seismic (PS) testing for the integrity testing of cemented soil columns are in- troduced in this paper. A three-dimensional (3D) finite element model (FEM) for the pile-soil system is established for impulse responses. Under saturated soil or unsaturated soil condition, several vibrating velocity-time histories at different depths in parallel hole are obtained based on the numerical simulation. It shows that the length of the pile and the one-dimensional (1D) P-wave velocity in the pile can be determined easily from the features of the mentioned velocity-time histories. By examining the slopes of the first arrival time plotted versus depth or the depth where the amplitude of the first arrival significantly decreases, the length of the pile can be determined. The effects of the 3D P-wave propagation through the saturated soil and the defect of the cemented soil column on the velocity-time histories are also investigated.

Earthquake simulation test of circular reinforced concrete bridge column under multidirectional seismic excitation

Structures behave multi-directionally when subjected to earthquake excitation. Thus, it is essential to evaluate the effect of multidirectional loading on the dynamic response and seismic performance of reinforced concrete bridge columns in order to develop more advanced and reliable design procedures. To investigate such effects, a 1/4 scaled circular reinforced concrete bridge column specimen was tested under two horizontal and one vertical components of a strong motion that has long duration with several strong pulses. Damage progress of reinforced concrete columns subjected to strong excitation was evaluated from the test. The test results demonstrate that the lateral force response in the principal directions become smaller than computed flexural capacity due to the bilateral flexural loading effects, and that the lateral response is not significantly affected by the fluctuation of the axial force because the horizontal response and axial force barely reached the maximum simultaneously due to difference of the predominant natural periods between the vertical and the horizontal directions. Accuracy of fiber analyses is discussed using the test results.

Monotonic and Cyclic Pushover Tests of Wood Beam-Column Connections:Ancient Chinese Tenon Joint vs Typical and Simplified US Connections

Wood beam-column frame is a popular structural system in United States and in ancient China. Chinese wood beam-column frame structures showed better seismic resistance properties than the US ones.The tenon joint is one of the reasons.This study performed monotonic and cyclic pushover tests to understand the behavior of Chinese tenon joints versus the behavior of the commonly used US wood beam-column connections. The test results indicate that the typical US wood beam-column connection is very strong under monotonic loads.The ancient Chinese tenon joint has the best behavior under cyclic loads.

黄土-古土壤互层对土壤水分运移及土体微结构的影响

黄土地区地质灾害问题的发生大多与水在黄土中的入渗有关,而马兰黄土-古土壤互层结构对土壤水分入渗规律的影响显著。为揭示古土壤阻滞作用下黄土水分运移规律及其对黄土体微结构的影响,为黄土地区工程实践提供理论基础,该研究以陕西省泾阳县南塬的黄土为研究对象,采用土柱模型进行水分入渗试验,研究黄土-古土壤互层条件下土壤水分运移规律。在此基础上,通过微结构测试、分形维数和概率熵等指标的计算,分析黄土-古土壤互层条件下土壤水分运移对黄土微结构的影响。结果表明:古土壤层的透水性弱,湿润锋抵达黄土与古土壤界面处产生瞬态滞水,且随着入渗强度增加滞水时间增加;古土壤层影响下黄土与古土壤界面处的滞水会导致孔隙结构相互连通,孔隙空间平均增加4.13%,孔隙方向概率熵平均减少0.029,分形维数平均减小0.076,即古土壤层的阻水作用使得界面处黄土的孔隙空间增大,孔隙排列有序,孔隙形态规则。研究结果为黄土地区的工程建设和生态环境保护提供科学支撑。

盾构施工扰动对天津结构性黏土动力特性影响的试验研究

盾构隧道施工扰动会改变周围土体的应力、应变状态,破坏土的结构性,从而影响隧道后期的地震响应.通过共振柱试验和动单剪试验,分析了施工扰动对天津结构性黏土动剪切模量和阻尼比的影响.试验结果表明:施工扰动程度越大,平均应力归一化动剪切模量的初始值越小(应力释放程度较大的D4试样的平均应力归一化动剪切模量初始值为无应力释放的D1试样的74%),在相同剪应变下的归一化动剪切模量越小,动剪切模量的衰减速率越快,在相同剪应变下的阻尼比越大;土的结构性越弱,初始动剪切模量越小(无水泥掺量的B1试样的初始动剪切模量为4%水泥掺量的B4试样的59%),在相同剪应变下的动剪切模量越小,动剪切模量衰减速率越快,在相同剪应变下的阻尼比越大.盾构隧道施工扰动对结构性黏土动力特性的影响机理为:施工扰动会使结构性黏土的结构破损、结构性减弱,从而导致其归一化动剪切模量减小,动剪切模量衰减速率增大,阻尼比增大.因此,在进行盾构隧道抗震设计时应考虑前期施工扰动引起的结构性黏土的结构破损对动剪切模量的影响.

Dynamic Performance Test and Estimation of Reinforcement Effect on a Workshop after Column-Cut Supported by Joist

The reinforcement effect of a reconstruction scheme for a steel factory building was investigated using finite element method and dynamic performance test. The workshop concerned is a portal frame structure with four spans and two slope roofs, of which ten columns need cutting for expanding span. The design and reconstruction project of column-cut supported by joist were introduced, which includes column reinforcement, connection rebuilding between brackets and crane beams, and the changing of rigid joint into hinge joint. The construction scheme was put forward in the light of the characteristics of the reinforcement and reconstruction. Spot test of dynamic performance on the workshop and comparison with theoretical analysis results show that the column-cut supported by joist design is effective and the reconstruction project is successful.

Statistical Tests of the Validation of TCO Satellite Measurements, Recorded Simultaneously by TOMS-OMI (2005) and OMI-OMPS (2012-2018)

Two statistical validation methods were used to evaluate the confidence level of the Total Column Ozone (TCO) measurements recorded by satellite systems measuring simultaneously, one using the normal distribution and another using the Mann-Whitney test. First, the reliability of the TCO measurements was studied hemispherically. While similar coincidences and levels of significance > 0.05 were found with the two statistical tests, an enormous variability in the levels of significance throughout the year was also exposed. Then, using the same statistical comparison methods, a latitudinal study was carried out in order to elucidate the geographical distribution that gave rise to this variability. Our study reveals that between the TOMS and OMI measurements in 2005 there was only a coincidence in 50% of the latitudes, which explained the variability. This implies that for 2005, the TOMS measurements are not completely reliable, except between the -50° and -15° latitude band in the southern hemisphere and between +15° and +50° latitude band in the northern hemisphere. In the case of OMI-OMPS, we observe that between 2011 and 2016 the measurements of both satellite systems are reasonably similar with a confidence level higher than 95%. However, in 2017 a band with a width of 20° latitude centered on the equator appeared, in which the significance levels were much less than 0.05, indicating that one of the measurement systems had begun to fail. In 2018, the fault was not only located in the equator, but was also replicated in various bands in the Southern Hemisphere. We interpret this as evidence of irreversible failure in one of the measurement systems.

内蒙古芒来铀矿石酸法柱浸试验

为获得溶浸液在不同硫酸质量浓度条件下的铀浸出特征及试验参数,探究内蒙古芒来铀矿床矿石酸法浸出的可行性,开展了不同硫酸质量浓度(5、10、15、20 g/L)的溶浸液下室内柱浸浸铀试验。试验结果表明,随着溶浸液硫酸质量浓度的增高,浸出液铀质量浓度及铀浸出率随之增高,浸出周期缩短,故酸法工艺适合该矿床铀浸出。试验后期浸出液流量降低与长石类矿物的黏土化蚀变有关。针对铀平均品位为8.8×10^(-5)的矿石,铀浸出率为49.80%~54.35%,从浸出率、防堵塞及浸铀成本等方面综合分析,认为质量浓度为10 g/L的硫酸溶浸液较适合该铀矿酸法地浸开采。

RPC外包方钢管混凝土柱轴压受力性能研究

为了研究活性粉末混凝土(Reactive powder concrete,RPC)外包方钢管混凝土柱的轴压受力性能,以RPC厚度和长细比为参数,对6根构件开展轴压试验研究,探讨该类组合柱的破坏模式、受力机理、套箍效应和承载力。试验结果表明:外层RPC可为内部方钢管混凝土柱提供较强的约束力,在受力后期套箍效应凸显。随着RPC厚度的增加,组合柱的承载力逐渐提高;随着组合柱长细比的增大,虽然其弹性刚度和承载力逐渐降低,但延性改善。采用ABAQUS软件建立RPC外包方钢管混凝土柱的有限元模型,分析RPC强度、RPC厚度、钢管强度等级、含钢率、内部混凝土强度和长细比等参数对组合柱承载力的影响规律,可得方钢管混凝土柱发挥系数的变化幅值为0.78~1.01。在试验研究、有限元参数分析和理论探讨的基础上,借鉴钢管混凝土结构技术规范,提出了RPC外包方钢管混凝土轴压短柱和长柱的承载力简化计算方法,公式计算值与已有数据样本吻合良好。

Analysis and seismic tests of composite shear walls with CFST columns and steel plate deep beams

A composite shear wall concept based on concrete filled steel tube （CFST） columns and steel plate （SP） deep beams is proposed and examined in this study. The new wall is composed of three different energy dissipation elements： CFST columns; SP deep beams; and reinforced concrete （RC） strips. The RC strips are intended to allow the core structural elements - the CFST columns and SP deep beams - to work as a single structure to consume energy. Six specimens of different configurations were tested under cyclic loading. The resulting data are analyzed herein. In addition, numerical simulations of the stress and damage processes for each specimen were carried out, and simulations were completed for a range of location and span-height ratio variations for the SP beams. The simulations show good agreement with the test results. The core structure exhibits a ductile yielding mechanism characteristic of strong column-weak beam structures, hysteretic curves are plump and the composite shear wall exhibits several seismic defense lines. The deformation of the shear wall specimens with encased CFST column and SP deep beam design appears to be closer to that of entire shear walls. Establishing optimal design parameters for the configuration of SP deep beams is pivotal to the best seismic behavior of the wall. The new composite shear wall is therefore suitable for use in the seismic design of building structures.

铰接方钢管组合异形柱框架抗震性能研究

为解决村镇住宅体系存在的装配式程度及标准化程度较低、现场焊接工作繁多、室内建筑面积浪费等问题,提出了一种铰接方钢管组合异形柱框架体系。该体系中异形柱采用3根空钢管通过钢板与加劲肋组合而成的L形柱,梁柱节点为腹板螺栓连接的铰接节点。通过拟静力试验对该体系的抗震性能进行研究。研究结果表明:相比于铰接钢管混凝土组合异形柱,铰接空钢管组合异形柱框架体系先于梁端出现转角,最后破坏模式为柱脚破坏,具有更优良的抗震耗能和更缓慢的强度与刚度退化,并通过对比刚接节点和铰接节点的骨架曲线,发现节点刚接程度对结构整体的抗侧刚度影响较大。

预制拼接槽型UHPC柱偏心受压性能试验研究

为研究预制拼接槽型UHPC柱在受压条件下的力学性能及其影响因素,开展2根整浇UHPC柱及14根预制拼接槽型UHPC柱在不同拼接形式、不同偏心受压方向及不同偏心距下的轴心或偏心受压试验研究.通过考察试件的极限承载力、破坏形态、轴向及侧向变形性能,研究了拼接方式、偏压方向和偏心距对其静力性能的影响.试验结果表明:钢纤维延缓了UHPC的开裂,增强了试件的变形能力,但预制拼接槽型UHPC柱在轴压和小偏压荷载下仍表现出明显脆性破坏特征;在该试验中,偏压柱的破坏形态主要为小偏心受压破坏及大偏心受拉破坏;在相同偏心距下,不同拼接形式、不同偏心受压方向的柱体破坏形态及承载能力表现趋于一致;在相同尺寸与配筋下,预制拼接槽型UHPC柱承载力随偏心距的增加而减小.最后,通过对比试件承载力试验值和我国现行规范理论计算值,定性地指出了现行规范的局限性.本文试验数据可为预制拼接槽型UHPC柱设计提供参考.

铬污染土壤动态浸出特征及对地下水影响的模拟

以原长沙铬盐厂污染土壤为研究对象,利用动态淋溶试验,研究不同淋溶模式下土壤六价铬[Cr(Ⅵ)]淋出特征及其对地下水的影响。结果显示,淋溶流速会影响土柱中Cr(Ⅵ)达到解吸稳定所需要的时间,即在连续淋溶模式的高、中、低3种流速条件下,达到平衡的时间分别为1、4、15 d,而间歇淋溶模式的Cr(Ⅵ)浸出效率略低于连续淋溶模式,这主要是受到土壤中孔隙水更新效率的控制。利用COMSOL Multiphysics?5.6构建试验中Cr(Ⅵ)迁移的模型,计算连续、间歇2种淋溶模式下6种不同情景中Cr(Ⅵ)的质量浓度变化及累积浸出质量,结合模型计算与柱实验结果分析发现,当土壤中Cr(Ⅵ)质量分数达到二类用地筛选值(5.7 mg/kg)后,淋出液中Cr(Ⅵ)质量浓度仍为地下水Ⅴ类水标准(0.1 mg/L),此时淋出液中Cr(Ⅵ)质量浓度仍对地下水环境造成威胁;同一时间段内,间歇淋溶柱高流速情景下有最小淋出率(33.67%),连续淋溶柱高流速情景有最大浸出率(83.99%)。研究表明,在场地地下水污染治理过程中,需要考虑土壤修复标准对地下水的影响,即水土共治。研究成果可为重金属污染场地修复工程提供参考。

某难处理金矿生物预氧化

某金矿石中黄铁矿含量5.31%、氧化率6.02%,直接氰化金浸出率仅27.78%,属典型的低品位硫化物包裹型难处理金矿。为评估生物堆浸预氧化工艺对该矿石的工业化应用前景,开展了直接氰化试验、生物搅拌预氧化-氰化试验和生物柱浸预氧化-氰化试验,考察了黄铁矿氧化率和金浸出率的关系以及温度对黄铁矿氧化率和金浸出率的影响。生物柱浸试验获得良好指标:原生矿破碎至D80=5.5 mm,在室温条件下(8~30℃)预氧化221 d后,黄铁矿氧化率52.30%,金的浸出率为62.70%,氰化渣金品位为0.47 g/t,较直接氰化浸出金浸出率(27.78%)提高34.92个百分点。

两矿法氧化难处理金矿中的黄铁矿

对黄铁矿-软锰矿两矿法酸性浸出工艺进行了研究,考察了硫酸浓度、配矿比、反应时间、液固比、反应温度等因素对浸出率的影响,确定了单矿物最适宜的浸出条件,并在此基础上开展了甘肃某地难处理金矿的浮选金精矿预氧化-氰化浸出试验研究。结果表明,当配矿质量比FeS_(2)∶MnO_(2)=1∶6,反应温度90℃,液固比6∶1,初始硫酸浓度100 g/L,预氧化时间为12 h时,锰的浸出率达到76.0%。此时,黄铁矿的氧化率达到88.2%,预氧化渣氰化处理后金浸出率达到85.4%。

新型钢管混凝土梁柱节点力学性能试验研究

为研究内加强环式圆钢管混凝土柱与矩形钢管混凝土梁这种新型连接节点的力学性能,设计了缩尺钢管混凝土梁柱节点试件,开展了相同梁柱节点试件的静力加载试验和低周往复加载试验。通过研究该节点试件的破坏模式、荷载-位移曲线以及拟静力加载试验的骨架曲线、核心区剪切变形等,分析了节点试件的承载能力、延性和耗能能力,全面考察了同一梁柱节点在静力加载和低周往复加载两种工况下的受力性能和破坏模式。结果表明:钢管混凝土梁柱节点试件核心区强度较强,破坏模式主要为梁端破坏,低周往复加载试验时试件梁柱连接处附近的梁端钢板发生拉裂破坏和钢板鼓曲,静力加载试验时试件梁端焊缝发生拉裂破坏;试件延性较好,加载过程中经历了弹性、弹塑性和塑性发展阶段。最后提出了该类钢管混凝土梁柱节点核心区的抗剪强度计算公式。

重载铁路双柱式桥墩加固技术优化研究

为探索基于性能提升的桥墩加固优化设计方法,以重载铁路中数量较多的分离式双柱式桥墩为对象,基于数值模拟分析和桥墩加固运营性能试验,开展3种常用方法加固条件下的桥墩静力性能对比分析和动力性能对比试验研究,并进行加固技术优化研究.结果表明,设计荷载作用下,墩身外包加固抑制墩顶水平位移效果较好,而"增大基础和增补桩基"组合加固则能有效减少基底截面应力;运营列车作用下,3种方法加固条件的墩顶横向振幅较加固前均有不同程度降低,但也有部分桥墩受施工等因素影响出现振幅增大的情况.采用优化提出的"增大基础+增补桩基+墩身外包"三重加固法,墩顶横向振幅降低幅度超过50%,能够很好地满足重载铁路双柱式桥墩强化改造需求.

橡胶加筋膨胀土共振柱动力特性试验研究

废弃橡胶可以较好地改良膨胀土的力学性能及胀缩特性,本试验考虑不同初始条件对橡胶加筋膨胀土(Expansion Soil-Rubber,ESR)动剪切模量影响,采用NGZ-20共振柱试验机开展不同含水率、橡胶掺量和颗粒粒径的系列研究,得到了不同初始条件下ESR的最大动剪切模量、动剪切模量与剪应变的变化规律。试验结果表明:随橡胶掺量和含水率的增加,加筋土的最大动剪切模量降低;在1×10^(-6)<γ<1×10^(-4)剪应变范围内,动剪切模量衰退明显,橡胶掺量变化较含水率改变对动剪切模量衰减影响更为显著;橡胶粒径对最大动剪切模量影响明显,但对动剪切模量衰减曲线影响不大。试验所得动力参数可以为橡胶改良膨胀土工程应用提供参考。