Infiltration characteristics of non-aqueous phase liquids in undisturbed loessal soil cores

The widespread contamination of soils and aquifers by non-aqueous phase liquids （NAPL）, such as crude oil, poses serious environmental and health hazards globally. Understanding the infiltration characteristics of NAPL in soil is crucial in mitigating or remediating soil contamination. The infiltration characteristics of crude and diesel oils into undisturbed loessal soil cores, collected in polymethyl methacrylate cylindrical columns, were investigated under a constant fluid head （3 era） of either crude oil or diesel oil. The infiltration rate of both crude and diesel oils decreased exponentially as wetting depth increased with time. Soil core size and bulk density both had significant effects on NAPL infiltration through the undisturbed soil cores; a smaller core size or a greater bulk density could reduce oil penetration to depth. Compacting soil in areas susceptible to oil spills may be an effective stratage to reduce contamination. The infiltration of NAPL into soil cores was spatially anisotropic and heterogeneous, thus recording the data at four points on the soil core is a good stratage to improve the accuracy of experimental results. Our results revealed that crude and diesel oils, rather than their components, have a practical value for remediation of contaminated loessal soils.

Colloid-facilitated release of polybrominated diphenyl ethers at an e-waste recycling site: evidence from undisturbed soil core leaching experiments

Polybrominated diphenyl ethers (PBDEs), a class of persistent organic pollutants, have been frequently detected in soil at e-waste recycling sites. However, the key factors controlling the transport of PBDEs from surface soil to the vadose zone and groundwater are unclear. Here, colloid-enhanced leaching of PBDEs from undisturbed soil cores collected at an e-waste recycling site in Tianjin, China, is reported. Spatially heterogeneous release of colloids and PBDEs was observed in all the tested soil cores under chemical and hydrodynamic perturbations, indicating the presence of preferential flow paths. Colloid concentration in the effluent significantly increased as ionic strength decreased (from 10 to 0.01 mmol/L), probably due to the stronger electrostatic repulsion between colloidal particles and the soil matrix at lower ionic strength. In contrast, colloid mobilization was not significantly affected by the changes in pH of the influent (from 4.0 to 10.0) and flow rate (from a Darcy velocity of 1.5 to 6.0 cm/h). The concentrations of 2,2′,3,3′,4,4′,5,5′,6,6′-decabromodiphenyl ether (BDE-209), the predominant PBDE congener at the site, detected in the leachate (ranging from 1.09 to 3.43 ng/L) were much lower than previously reported results from packed column leaching tests, and were positively correlated with colloid concentrations. This indicates that remobilization of colloids at e-waste recycling sites can promote the leaching and downward migration of PBDEs from surface soil. The findings highlight the potential risk of surface soil PBDE contamination to groundwater quality and call for further understanding of colloid-facilitated transport for predicting the fate of PBDEs at e-waste recycling sites.

Vertical distribution of rare earth elements in a wetland soil core from the Sanjiang Plain in China

The objective of this study was to investigate the vertical distribution of rare earth elements （REEs） in a natural wetland soil core to understand the influence of natural and anthropogenic activities on geochemical behavior of REEs. A natural wetland soil core of 95 cm was collected from the Sanjiang Plain in China and sliced into 5 cm slices for analyses of REEs, Fe, Al, Mn, Sc, Y, and soil organic matter （SOM）. Results indicated that SOM was accumulated in the upper part of the soil core （0 to 20 cm depth）, while Fe and Mn was reductively leached from the upper part of the soil core and accumulated in the low part. The content of total REEs ranged from 137.9 to 225.9 mg/kg in the soil core. Content profiles obtained for all REEs were almost identical except for Ce. The highest contents of REEs generally occurred at about 20 cm depth, but enrichment factor （EF） of REEs except Ce was usually the highest in the surface horizon. Average EF ranged from 1.1 for La to 2.1 for Gd. The pronounced shift in EF occurred at about 40 cm depth and it gradually increased from 40 cm depth to surface （except for Ce）, probably suggesting anthropogenic atmospheric deposition of REEs. In comparison with chondrite, Eu was depleted in all horizons, while Ce was negatively anomalous in the top horizons and positively anomalous in the bottom horizons. This positive anomaly of Ce in the bottom horizons was due to its preferential adsorption on Fe and Mn oxides, relative to other REEs. Although both natural and anthropogenic activi-ties influence the geochemical behaviors of REEs in soils, enrichment or mobility of REEs is low in the natural wetland soil core of the San-jiang Plain.

预留核心土法隧道爆破围岩损伤与振动特性研究

目的 研究预留核心土法爆破开挖影响下的山岭隧道围岩损伤与振动特性,为爆破参数优化以及隧道加固设计提供理论参考。方法 依托新疆阿克特蒲2号左洞隧道工程,借助ANSYS/LSDYNA软件建立隧道爆破开挖数值模型,基于现场实际开挖轮廓和振速监测数据验证数值模型的合理性,进而分析围岩累积损伤特性、振速分布和振速衰减规律。结果 爆破结束后,隧道轮廓平整,预留核心土上部损伤严重;隧道拱顶y方向、拱肩z方向及拱脚x方向的振速最大;距离掌子面越近,采用萨道夫斯基经验公式预测的振速结果误差越大。结论 为保证结构稳定性,在下次爆破施工前可以通过减少掏槽孔、辅助孔的装药量或者调整其孔网参数来减小爆炸荷载,沿最大振速方向进行重点加固;采用萨道夫斯基经验公式预测距离掌子面10 m内的振速时,避免仅用z方向距离近似为爆心距大小,应同时考虑三个方向的距离。

混凝土芯水泥土复合桩竖向承载特性分析方法

基于Euler梁理论和状态空间法,建立了综合考虑非线性芯桩-水泥土-桩周土界面作用的双层叠合直梁分析模型及其状态方程,推导了成层土中不同组合形式的复合桩截面内力与变形的统一解析解,有效地考虑了复合桩分析中土与结构相互作用、结构局部参数发生变化等难点。通过与已有文献中现场试验和数值计算结果对比,验证了该方法的有效性,并讨论了桩径比、芯长比和水泥土弹性模量对桩承载特性的影响。研究结果表明:(1)桩径比增大,可提供的桩侧摩阻力和桩端阻力增大,复合桩竖向承载力基本呈线性增长;(2)芯长比增大,复合桩竖向承载力的增长幅度逐渐增大;(3)水泥土弹性模量对于桩竖向承载力影响较小。

梅雨气候区膨胀土填芯路基设计研究

将膨胀土作为路基填料,可有效利用膨胀土路堑开挖产生的弃土。以铜陵江北港铁路专用线膨胀土路基工程为依托,提出了梅雨气候区膨胀土填芯路基的设计方法。首先,进行膨胀土的膨胀力试验;然后,研究梅雨季节膨胀土填芯路基内部体积含水量与包边黏性土种类、包边厚度、路基压实系数的关系,分析梅雨季节填芯膨胀土膨胀力发育情况;最后,确定了膨胀土填芯路基设计方案,并将膨胀力引入折线型滑动面安全系数计算公式进行稳定性验算。结果表明,铜陵江北港铁路专用线膨胀土填芯路基采用亚黏土包边,包边厚度取1 m,压实系数取0.92,不仅能减少浪费,安全系数也满足规范要求。

浅埋软弱围岩隧道掌子面锚杆预加固参数分析

大断面浅埋隧道在软弱围岩中全断面开挖时,隧道掌子面核心土处于短暂稳定或不稳定状态,处理不慎便会造成核心土的失稳,因此采用玻璃纤维锚杆对核心土进行预加固是有必要的。结合格鲁吉亚某隧道工程实例,采用新意法理念,运用FLAC3D有限差分软件,对浅埋软弱围岩隧道全断面开挖时掌子面玻璃纤维锚杆加固长度l(5个工况)和加固密度β(7个工况)进行优化分析,结果表明:随着l或β的增大,目标掌子面挤出位移和拱顶前方位移逐渐减小,目标掌子面拱顶前方应力逐渐趋于原始状态;当l>6 m或β>0.75时,掌子面锚杆对核心土的预加固效果不明显,综合工程的安全性和经济性,取l=8 m、β=0.75较为合理,为类似工程提供了一定的参考依据。

基于新意法理念的隧道施工方法研究

随着我国隧道建设重心的逐步西移,所涉及的工程地质条件和地应力情况愈发复杂,运用传统隧道施工方法存在诸多问题,如难以克服大变形问题、无法在施工过程中精准预测隧道变形特征等。新意法理念为这些问题的解决提供了新的思路。为推广新意法施工设计理念,系统性论述了新意法的基本原理及其设计施工相关流程,并在此基础上分析与传统工法相比其优势所在,为相关工作人员提供参考与指导。

高土石坝心墙砾石土料掺配施工技术

高砾石土心墙土石坝防渗体砾石土料的质量对坝体结构稳定和长期安全运行至关重要,通过对不同土料掺配施工技术研究,制定出精确掺配的相关施工工艺参数,解决了常规施工存在的诸多问题,提高了高土石坝砾石土料掺拌和填筑施工质量,节约了工程施工成本,确保了坝体结构稳定和运行安全,为工程正常有序施工及完建创造了良好的条件。

软弱围岩隧道三台阶预留核心土带仰拱一次开挖工法定额测定研究

在软弱围岩隧道施工过程中,合理确定隧道开挖施工技术及投资是铁路建设者需要关注的重点问题之一。本文选取玉磨铁路立新隧道和月牙田隧道相关工点进行现场调研和数据统计,采用写实统计法和现场测定法,分析工法方案和要求,收集测定现场工料机组成及费用情况,并与正常施工条件下的数据进行对比分析,提出三台阶预留核心土带仰拱一次开挖工法定额。为铁路相关部门下一阶段造价标准修订补充、完善隧道工程的预算定额体系、促进我国铁路投资控制良性发展提供了技术支撑。

黏土心墙堆石坝防渗土料掺配加工技术研究

针对土石坝项目因周边环境、水文地质不良以及征地问题造成的土料场料源储量少、质量不合格等问题,笔者以广西蒙山古皂水库为例,分析土料加工控制原理,研究土料开采、加工、运输等环节的控制措施,总结出控制黏土心墙堆石坝防渗土料质量优化的施工技术,提出适用于该项目的防渗土料掺配加工工艺。结果表明:所提出的工艺将土料生产效率从600 m3/d提高到850 m3/d,效率提高了41.67%;大坝心墙填筑工期由原计划的12个月缩减至9个月。研究成果可为土石坝土料加工提供参考。

黄土区大跨度隧道开挖技术探讨

临洮(安家咀)至临夏一级公路百和隧道均为Ⅴ级围岩,主要有黄土浅埋段、岩质地段、黄土深埋段、小净距段以及黄土深埋段等情况,针对不同的围岩情况和地质条件,有针对性的采用CD法、上下台阶留核心土法及三台阶分步法进行开挖。

海相淤泥质黏性土加芯搅拌桩竖向承载特性室内模型试验

加芯水泥土搅拌桩结合了搅拌桩与钢筋混凝土预制桩的优点,弥补了双方的缺点,是一种正在被广泛推广的深厚淤泥质软土复合地基处理方式。文章通过采取加芯水泥土搅拌桩单桩、复合地基竖向承载室内模型试验,研究等芯桩、短芯桩的竖向承载特性,得到单桩承载力、桩侧阻力、桩身轴力、桩土应力比的变化关系。试验结果表明,加芯水泥土搅拌桩具有更强的单桩承载力,能显著提高传统水泥土搅拌桩的承载能力。

甘青青兰根际土壤理化性质及微生物群落结构特征分析

为研究甘青青兰根际土壤理化性质与根际土壤细菌和真菌群落结构组成特征,以西藏自治区工布江达县(GB)、卡诺区(KR)和洛隆县(LL)的甘青青兰根际土壤微生物为研究对象,采用IlluminaMiSeq高通量测序技术对根际土壤细菌和真菌群落结构组成进行分析,同时测定根际土壤的理化性质,并与根际土壤核心微生物菌群进行相关性分析。结果表明,不同地区甘青青兰根际土壤理化性质差异显著。甘青青兰根际土壤共获得3900个细菌OTUs和1990个真菌OTUs,不同地区间土壤微生物多样性存在明显差异。在门水平,GB、KR和LL样品的优势细菌门均为放线菌门(Actinobacteria),GB样品的优势真菌门是担子菌门(Basidiomycota),KR和LL样品的优势真菌门是子囊菌门(Ascomycota);在属水平,不同地区甘青青兰根际土壤优势微生物菌群存在明显差异。主成分分析显示,不同地区甘青青兰根际土壤细菌和真菌群落结构组成差异较大。核心微生物菌群分析表明,甘青青兰根际土壤核心细菌菌群有257个属;核心真菌菌群有102个属。相关性分析表明,核心微生物菌群的改变与根际土壤理化因子间存在不同程度的相关性,且土壤全钾、全磷、全氮、速效钾和速效氮含量是影响甘青青兰根际土壤微生物群落结构组成的重要因子。综上所述,不同地区甘青青兰根际土壤微生物群落结构组成存在显著差异,且根际土壤微生物群落结构的变化与土壤理化因子密切相关,为甘青青兰人工种植及筛选有益微生物菌群提供了理论依据。

基于孔压静力触探的心墙黏土水平渗透系数测定方法研究

为了提出一种准确快速的土石坝心墙黏土渗透系数测定方法,基于孔压静力触探建立了渗透水流的椭球形水平渗流模型,该模型可以较好的适用于夯实土体的水平向渗透系数评估。首先回顾了前人基于孔压静力触探测算土体渗透系数的研究成果,再从实际角度出发,分析推导了探头贯入土体产生超静孔隙水压力分布的力学模型,与实测数据对比后认为超静孔隙水压力负指数函数分布形式具有一定准确性。然后推导了基于椭球形水平向渗流模型的渗透系数评估方法。经工程实例验证,本文方法从理论和计算精度等方面对前人方法进行了完善,具有较好的工程应用前景。

砾石土料的湿化变形试验技术难点与解决方法

砾石土心墙料的大尺寸样品湿化变形试验难度极大,这主要是砾石土料的性质决定了其饱和固结排水困难、样品难以达到饱和状态、试验周期太长。从试验技术、测试方法等方面进行攻关,分析试验成果出现偏差的原因并修正,针对砾石土湿化变形离散性大、存在应力饱和问题,进行了艰难地研究探索。通过对湿化试验过程中的体变修正、进水量修正、饱和度实时计算、成果离散性处理等关键细节的严格把控,最终成功地完成了典型砾石土料的湿化变形试验,获得了规律性较好的砾石土心墙料湿化变形成果。试验过程中出现的异于常规的现象,如围压施加过程中三轴压力室的整体向上变形、高应力状态下没有湿化变形量等,通过试验数据分析和理论分析,最终都得到了合理的解释,加深了对砾石土心墙料土工试验技术和砾石土料湿化变形的认识。

砾石土心墙料的湿化变形特性试验研究

针对砾石土心墙料,采用大型应力式三轴仪开展了单线法湿化变形试验,较系统地研究了湿化应变与应力水平、围压之间的变化规律。依据试验成果,砾石土心墙料的湿化变形是明显的,且与应力水平、围压密切相关,在高围压、高应力水平条件下,外力改变了试样的饱和状态,砾石土样品逐渐从非饱和状态过渡到饱和状态,砾石土料存在应力饱和现象,导致湿化过程中没有明显的湿化变形。当围压较小时,湿化应变随应力水平的增大而增大,当围压增大到一定量值时,湿化应变反而随应力水平的增大而减小,呈现明显的分叉现象,表现出更加复杂的规律。最后提出了砾石土料湿化变形模型及模型参数,提出的砾石土料湿化模型可作为高土石坝湿化变形分析的基础。

基于FOA-RF算法的心墙砾石土压实质量预测模型

针对随机森林(RF)算法预测心墙砾石土压实质量存在决策树数量选取缺乏深入研究和忽视P0.075质量分数对压实质量影响的问题,提出了一种基于果蝇优化(FOA)算法的随机森林算法(FOA-RF算法),并构建了基于FOA-RF算法的心墙砾石土压实质量预测模型(FOA-RF模型)。该模型一方面通过对料源参数和干密度进行相关性分析,新增了P0.075质量分数作为模型的输入参数;另一方面利用FOA算法对随机森林进行优化,解决了RF算法难以取得决策树数量最优解、没有同时考虑决策树数量与随机特征数影响的问题。以西南某在建砾石土心墙堆石坝工程为例,分别应用基于传统RF、BP神经网络、多元线性回归的预测模型和FOA-RF模型进行压实质量预测。结果表明,FOA-RF模型在预测精度上具有优越性,并基于该模型开发压实质量预测模块,将该模块嵌入碾压质量实时监控系统中可实现压实质量的实时预测。

Comparing Two Methods for Measuring Soil Bulk Density and Moisture Content

Soil bulk density and moisture content are dynamic properties that vary with changes in soil and field conditions and have many agricultural, hydrological and environmental implications. The main objective of this study was to compare between a soil core sampling method (core) and the CPN MC-3 EliteTM nuclear gauge method (radiation) for measuring bulk density (ρB) and volumetric moisture content (θv) in a clay loam soil. Soil ρB and θv measurements were determined using the core and radiation methods at 0 - 10 and 10 - 20 cm soil depths. The mean values of soil ρB obtained using the core method (1.454, 1.492 g·cm−3) were greater than those obtained using the radiation method (1.343, 1.476 g·cm−3) at the 0 - 10 and 10 - 20 cm depths, respectively. Mean ρB and θv values averaged across both depths (referred to as the 0 - 20 cm depth) measured by the core method were 4.47% and 22.74% greater, respectively, than those obtained by the radiation method. The coefficients of variation (CV) of soil ρB values measured by the core method were lower than the CV values of those measured by the radiation method at both depths;however, the CV’s of ρB values for both methods were larger at the 0 - 10 cm depth than those measured at the 10 - 20 cm depth. Similarly, the CV values of soil θv values measured by the core method were lower than the CV values of those measured by the radiation method at both depths. There were significant differences between two methods in terms of ρB and θv, with the core method generating greater values than the radiation method at the 0 - 20 cm depth. These discrepancies between the two methods could have resulted from soil compaction and soil disturbance caused by the core and radiation techniques, respectively, as well as by other sources of error. Nevertheless, the core sampling method is considered the most common one for measuring ρB for many agricultural, hydrological and environmental studies in most soils.

基于CNKI核心期刊数据的土壤团聚体文献计量分析

为了解2001~2020年土壤团聚体相关领域的研究现状,作者以中国知网(CNKI)中文核心期刊文献为研究对象,选用高级检索方式,以“土壤”AND“团聚体”为主题词,从年度发文量、主要发文期刊、发文机构、作者发文量、高被引论文、高频关键词等角度,对近20年土壤团聚体领域的文献进行计量分析,研究结果可为土壤团聚体领域进一步的研究提供参考依据。