躺滴法测量干湿循环条件下土壤固-液接触角的滞后特性

接触角滞后是使土壤的土水特征曲线产生滞后现象的主要因素之一,而土水特征曲线的滞后特性是土壤干湿循环的显著特征。该文采用混合制样法制备不同接触角的土样,通过躺滴法对干湿循环过程中土体的固-液接触角随时间的变化关系进行测量,结果表明:随着土样表面固滴的蒸发,其固-液接触角是不断减小的,且初始接触角越大,固滴完全蒸发所用的时间越长,黏土接触角随时间变化关系曲线呈线性,而砂土的则表现出一定的非线性。不论土体的初始接触角多大,临近固滴蒸发结束,接触角都会变为0,且整个蒸发过程中固-液-气三相接触线不发生移动,固-液接触面积保持不变。试验结果证实了土壤脱湿过程把固-液接触角假设为0是合理的,并且可以断定接触角滞后特性也可能是非饱和土土水特征曲线在反复干湿循环下滞回圈不断减小的原因之一。     

干湿循环对土壤斥水性的影响

处于地表的各类土壤总是处于不断的干湿循环过程,土壤性质也会因此而发生改变。本文通过试验对干湿循环过程中斥水性土壤的"斥水–亲水"特性展开研究,试验结果表明:干湿循环对斥水性土壤的接触角及斥水性有重要影响。在干湿循环过程中,增湿时的初始状态不同则其初始接触角会发生变化,土壤斥水性对初始状态的敏感性随着黏粒含量的增加而增大。干湿循环开始时,土壤越干则初始接触角越大。当黏土和黏壤土试样含水量减小时,增湿或脱湿过程中滴水穿透时间(waterdroppenetrationtime,WDPT)先增加后减小,在某一时刻达到峰值,试样含水量相同时,脱湿过程所对应的WDPT要明显小于增湿过程,两种类型的土样在干湿循环中均没有临界含水量。随着含水量的降低,壤质砂土的WDPT是不断增加的,且干湿循环过程中斥水性砂土并没有出现峰值,存在明显的临界含水量。     

干湿循环下云南非饱和红土土—水特性研究

以云南红土为研究对象,以脱湿、吸湿引起的干湿循环作为控制条件,考虑初始干密度(1.20,1.25,1.30g/cm3)、初始含水率(30.0%,33.0%,36.0%)、预固结压力(0,50,100,200kPa)、过筛粒径(0.5,1.0,2.0mm)等影响因素,通过压力板仪法,研究干湿循环下云南非饱和红土的土—水作用特性。结果表明:干湿循环过程中,不同影响因素下红土的基质吸力随含水率的增大而减小,其土—水特征曲线呈直线型或"倒J"形,其脱湿变化过程可以分为快速脱湿、缓慢脱湿、稳定脱湿3个阶段,对应的吸湿变化过程也可以分为快速吸湿、缓慢吸湿、稳定吸湿3个阶段。相同基质吸力下,随初始干密度、初始含水率、预固结压力的增大,红土的含水率增大;随粒径的增大,红土的含水率减小。初始干密度、预固结压力、粒径(0.5mm除外)影响下的红土的土—水特征曲线可采用幂函数关系进行拟合,不同初始含水率、粒径0.5mm时的土—水特征曲线可采用线性函数关系进行拟合。红土脱湿过程的含水率高于吸湿过程的含水率,脱湿—吸湿过程中的土—水特征曲线存在滞后现象,其实质在于干湿循环作用下红土具有孔隙效应、瓶颈效应、角度效应的综合结果。     

伊毛缟石对蒙脱土和高岭土分散凝聚特性的影响

[目的]探究伊毛缟石对蒙脱土和高岭土分散凝聚特性的影响,为水土保持和环境保护工作提供理论依据。[方法]采用浊度法测定黏土的分散性、离子交换法测定黏土电荷特性、电子显微镜观察等实验方法,将蒙脱土和高岭土溶液分别按一定比例混合伊毛缟石溶液,观察伊毛缟石对蒙脱土和高岭土分散凝聚特性的影响。[结果]伊毛缟石和蒙脱土的1∶1混合溶液,在全部pH值范围内保持凝聚;未脱铁处理的高岭土在pH值为5.9以下凝聚,在pH值为6.0以上分散,添加约5%的伊毛缟石使它的分散凝聚特性逆转。[结论]从微观上看,无论在酸性还是碱性条件下,伊毛缟石混合溶液都呈凝聚状态。酸性时,伊毛缟石的可变电荷和结晶性黏土矿物的永久电荷之间的引力形成凝聚;碱性时,伊毛缟石的表面变成中性形成凝聚。     

地面机械触土部件仿生涂层的减粘降阻特性

对研制的11种地面机械触土部件仿生涂层的减粘降阻特性进行了试验研究,探讨了触土部件表面形态、仿生涂层的固有接触角、土壤含水量及推土板切削速度对减粘降阻特性的影响,并测试了部分典型涂层与土壤的滑动阻力,分析了仿生涂层固有接触角对滑动阻力的粘附分量及涂层与土壤摩擦角的影响。     

测量土壤颗粒密度的体积置换法

土壤颗粒密度测量在土壤和水的关系研究和实践中有重要意义。该文提出一种采用体积置换测量土壤颗粒密度的方法。该方法可以从2种途径进行测定。第1种途径是湿土测量法。第2种途径是干土测量法。湿土测量法:将任意质量和含水量的湿润土样装入容积已知的恒容容器后,称量得到其质量,再将恒容容器中注满水,置换出容器和土壤充气孔隙中气体的体积,再称量得到容器中土颗粒与水的总质量,进而计算得到补水置换体积。然后将土样充分烘干测量得到土颗粒的质量,计算原始土样中土壤水的体积与质量,进而计算得到土颗粒体积,由此测得土粒密度。干土测量法:将土样充分烘干测定土颗粒质量,再将烘干土样置于恒容容器中并注满水,测量并计算得到补水所置换的容器和土壤孔隙的体积,由此确定出土颗粒体积,进而由土颗粒体积和土颗粒质量计算得到土粒密度。采用4种土壤:陕西杨凌的黏黄土、北京的粉壤土、吉林的黑土和江西的黏红土,配制成5种不同土壤含水率(10%、15%、20%、25%、30%)。用上述体积置换法的2种途径,分别测定了每种土壤的土粒密度,并将测得的结果与常规比重瓶法、容量瓶法的测量结果进行比较。试验结果表明,所采用的4种土壤,持续烘干72 h(105℃),湿土法测量得到的土粒密度分别为2.6576、2.6301、2.6411和2.6687 g/cm3,采用干土法测得土粒密度分别为2.6557、2.6320、2.6423和2.6660 g/cm3。4种土壤烘干8 h(105℃)可能使测量得到的土壤颗粒密度偏小1%~2%。土壤颗粒密度测量误差随着烘干时间的延长而逐渐减小。干土法和湿土法测量土壤颗粒密度的散点都聚集在1∶1线上,表明2种方法测量得到的结果基本相同,测量结果比较的最大相对误差小于0.5%,说明体积置换法2种途径可以达到同等测量效果。所提出的方法测量精准度高,操作过程优于常规比重瓶法和容量瓶法。     

基于光释光测年法的三江源地区高山草甸土形成年代与成因研究

[目的]分析三江源区高山草甸土壤的年代及发生发育过程,为维系该区土壤安全和生态安全提供指导.[方法]采用粗颗粒石英与钾长石光释光(OSL)测年法,对三江源区4个高山草甸土剖面夏琼(XQ)、歇武(XW)、桐勒栋(TLD)、斗地村(DDC)土壤的形成发育时间进行研究,结合土壤粒度、元素地球化学特征分析该区土壤形成过程.[结...     

犁壁材料表面特性与土壤粘附间的关系

选取机引犁壁和畜力犁壁，研究其表面特性与土壤粘附间的内在联系。首次将材料的土壤粘附特性与表面电化学现象联系起来，从理论与试验的结合上证明提高材料的耐蚀性有利于金属材料表面减粘脱土，为触土部件的材料选取、成分优化以及铁基减粘材料的研制提供了简捷有效的参考指标和理论依据     

黄土高原坝淤土发生特性与系统分类研究

[目的]黄土高原区沟坝地经过人工筑坝后自然淤积或者拦蓄洪水淤积而形成坝淤土,为了解坝淤土的发生特性及系统分类归属开展研究.[方法]为本文选取5个典型坝淤土剖面,分析坝淤土的成土环境、剖面形态特征理化性质,检索坝淤土在中国土壤系统分类高级及基层分类的归属.[结果]坝淤土剖面土体深厚,成土母质为人为淤积物质,色调以浊黄橙为...     

含水饱和度和含油饱和度对柴油污染土壤电阻率的影响研究

为研究含水饱和度和含油饱和度对石油污染土壤电阻率产生的影响,以柴油作为代表污染物,粉土、粉质亚粘土和砂土为研究对象,将其按不同油水比配制成污染土,利用Miller Soil Box法进行电阻率测试。结果显示,不同类型的污染土在相同的条件下电阻率存在差异,其中含水饱和度的影响大于含油饱和度。不同油水比砂土的电阻率变化最大,粉质亚粘土次之,粉土最小。随含水饱和度的增大,污染土电阻率呈幂函数降低,符合Archie公式,其中砂土的电阻率下降最快。初始含水率对柴油污染土电阻率影响较大,含水率为5%时,出现高阻石油污染低阻异常;含水率为15%时,电阻率随含油饱和度增大先降低后升高。     

Effects of hydrophobic and hydrophilic organic matter on the water repellency of model sandy soils

Soil water repellency affects the hydrological functions of soil systems. Water repellency is associated with the content and the composition of soil organic matter. In the present study, we examined the effects of hydrophobic and hydrophilic organic matter contents, the hydrophobic/hydrophilic organic matter ratio and the total organic matter content on water repellency using model sandy soils. Stearic acid and guar gum were used as the hydrophobic and hydrophilic organic compounds, respectively. Water repellency was estimated using the sessile drop method. Hydrophobic organic matter content was found to be the dominant factor affecting soil water repellency. Hydrophilic organic matter was found to increase the contact angle to some extent without the presence of hydrophobic organic matter. With the presence of both hydrophobic and hydrophilic organic matter, the effects of the hydrophilic organic matter content on contact angle were found to be dependent on the hydrophobic organic matter content of the soil. This relationship was explained by the differences in the surface free energies of different organic matter and mineral surfaces. The contact angle increased with increasing hydrophobic/hydrophilic organic matter ratio when the hydrophilic organic matter content was constant. When the hydrophobic organic matter content was constant, contact angles were roughly comparable, irrespective of the hydrophobic/hydrophilic organic matter ratio. The contact angles were not comparable at each total organic matter content. Accordingly, the hydrophobic/hydrophilic organic matter ratio and the total organic matter content in soil may not provide satisfactory information about soil water repellency.     

Universality of a surface tension—contact‐angle relation for hydrophobic soils of different texture

Wettability of soil affects a wide variety of processes in soils like infiltration, percolation, preferential flow, and surface runoff. Even though efforts have been made to determine contact angles and surface tension or energy of smooth surfaces, the determination on granular materials like soil particles remains unsolved. One objective of this study was to test the consistency of contact angles (CA) measured with the newly modified and easy‐to‐apply Wilhelmy plate method by using solid particles and liquids with defined variations of surface tension. A second objective was to derive basic physical surface properties for the irregularly shaped and chemically heterogeneous soil particles. Advancing contact angles were determined by using model soils varying in texture from clay to coarse sand to check the impact of grain size on the CA measurements. Varying the solid‐surface tension with dichlorodimethlylsilane treatments provided for pure‐water wetting stages ranging from wettable to extremely hydrophobic. The surface tensions of the liquids were varied from 72 mN m^–1 to 25 mN m^–1 by using water or water‐ethanol mixtures. The surface tensions of the model soils were determined with the zero degree–contact angle method following Zisman's critical–surface tension concept. Results show that the measured CA varied continuously with the variations of the surface tension of the liquid and the solid phase, respectively. A general interpretation of the results is possible by using the concept of the Equation of State Approach.     

化学非光滑表面和几何粗糙表面的润湿性

研究了弥散Al₂O₃粒子的尼龙1010基复合涂层和喷涂T8钢—浸渍聚有机硅氧烷的复合涂层两类化学非光滑表面及聚乙烯、聚苯乙烯、尼龙6、尼龙1010、T8钢、45钢和Al₂O₃粗糙表面的润湿性。导出了弥散球形粒子型化学非光滑表面上液体接触角与其组成相固有接触角关系的方程,该方程与尼龙1010—Al₂O₃粒子复合涂层表面接触角试验结果吻合良好。在尼龙1010基体中加入适量Al₂O₃粒子后,液体接触角未发生明显变化;T8钢喷涂层浸渍聚有机硅氧烷后,表面憎水性明显增强;材料的固有接触角越远离90°,表面粗糙性对接触角的影响越明显。     

烷基聚葡糖苷液滴在黄瓜叶面的润湿状态及动态铺展行为

为了探究烷基聚葡糖苷(alkyl polyglycosid,APG)在黄瓜叶面的动态润湿行为及其动态接触角变化规律,采用表面张力与接触角测量仪测量了一次去离子水和9种质量百分数APG水溶液(14.35%~85.78%)的表面张力、液滴叶面接触角与动态接触角、前进角与后退角、铺展直径等动态润湿参数。依据Tanner法则对接触角滞后现象、铺展驱动力成因进行分析和推测,并应用幂次法则拟合了铺展直径与幂值和时间的关系曲线。结果表明,9种APG水溶液的表面张力介于27.96~29.73 m N/m小幅范围内,而接触角却在11.35°~34.20°较大范围内变化;接触角滞后性(Δθ=46.89°)较大,反映出一次去离子水在活体植物黄瓜叶面的接触角变化符合粗糙表面上接触角滞后现象的基本规律;各质量百分数APG溶液的动态接触角在前1 s内急速下降,在之后1~10 s平稳减小并渐趋于稳定;APG在黄瓜叶面的铺展直径与时间的关系均较好地符合幂次法则,据此推测动态表面张力是黄瓜叶面(界面)占据绝对优势的铺展驱动力。     

面向结构参数的滚珠丝杠副动态接触角建模

为研究滚珠丝杠副结构参数对接触角的影响,基于Hertz理论和滚道控制理论,综合考虑滚珠、螺母和丝杠滚道的结构参数,以间隙、公称直径、滚珠直径、螺旋升角及滚珠数量作为变量,建立滚珠丝杠动态接触角模型,得到面向结构参数的接触角非线性方程组,给出采用Newton-Raphson法进行迭代求解的流程。基于动态接触角模型进行讨论和实例分析,研究不同工况下的结构参数对滚珠丝杠副动态接触角的影响规律。结果表明:工作中的滚珠丝杠副丝杠侧的内接触角始终大于螺母侧外接触角;滚珠与滚道间隙量增大0.1 mm,内、外接触角增大约7°;公称直径增加则外接触角减小、内接触角增大;滚珠直径和滚珠数量的增大会导致外接触角减小、内接触角先减小后增大;螺旋升角对接触角影响很小,内、外接触角变化幅值均不到0.006°。该研究为滚珠丝杠副结构尺寸优化、动态特性分析、提高设计精度提供了参考。     

微观尺度下黄土多级湿陷性研究

[目的]验证黄土多级湿陷性以及探究微观尺度下黄土的湿陷变形方式,为黄土的湿陷变形机理研究提供科学依据。[方法]分别设计、实施了室内循环加水湿陷试验和相同样品增湿前后微观结构观察试验,并分别对湿陷数据与扫描电镜影像进行分析和对比。[结果]湿陷数据表明,在黄土达到一次湿陷稳定以及去水稳定后,在装置内再次加水会导致试样再次发生明显形变,而黄土的微观结构在湿陷过程中发生了溶解、移动、重组三种变形方式。[结论]黄土结构这种破坏—重组—破坏的动态循环过程是黄土能够发生多级湿陷的内在原因。     

Time dependence of contact angle and its relation to repellency persistence in hydrophobized sand

Soil water repellency is a transient soil property varying with soil–water contact time. The purpose of the present study was to determine the time dependence of the sessile drop contact angle and its relation to repellency persistence estimated using the water drop penetration time (WDPT) test with hydrophobized sand. The contact angle decreased exponentially and almost reached apparent equilibrium after 20 min of soil–water contact time. Time dependence of the contact angle can mainly be attributed to the adsorption of water molecules onto low-energy hydrophobic organic matter surfaces. Contact angles initially greater than 90° decreased to less than 90° within about 40 s. However, the WDPT of these samples was longer than 3600 s. The WDPT responded to the initial contact angle, but not to the contact angle decreased with soil–water contact time. This was considered to be caused by differences in the surface free energy between the surface and the lower layers. Repellency persistence, or the WDPT, can be considered to be the time taken to increase the surface free energy to overcome water repellency, not only on the surface in contact with the droplet, but also in the adjacent layers below the surface.     

基于微观球体颗粒模型的土水特征曲线研究

When variations occur in the water content or dry bulk density of soil,the contact angle hysteresis will affect the soil-water characteristic curve(SWCC).The occurrence of the contact angle hysteresis can be divided into slipping and pinning.It is difficult to determine the effect of pinning existence on SWCC by tests.In this study,the effect of contact angle hysteresis on SWCC was analyzed either in the case of no variations in soil dry bulk density with changes in soil water content or no variations in soil water content with changes in soil dry bulk density.In both cases,soil particles were simplified to the spherical particle model.Based on the geometrically mechanic relationship between the particles and connecting liquid bridges,a physical model for predicting the SWCC was derived from the spherical particle model.Adjusting parameters made the model applicable to various soils,that is,the cohesive soil was considered as micron-sized spherical particles.Through the simulations on SWCC test data of sand,silt,clay,and swelling soil,it was confirmed that the physical model possessed good reliability and practicability.Finally,the analysis of rationality of contact angle was performed based on the basic assumptions of the model.     

上舍流域两种林地土壤结构与抗蚀性

[目的]为了解土壤侵蚀的机理,探究土壤抗蚀性与土地利用类型、土壤结构的关系。[方法]以安徽省岳西县毛尖山乡上舍村典型小流域马尾松林(Pinus massoniana Lamb)和桑树林(Morus alba L)为研究对象,在0—40cm土壤深度范围内,按照10cm间隔分层取样,室内测定土壤孔径、比表面积、崩解指数、不同径别(0.5,0.5~1.0,1.0~2.0和2.0~2.5mm)根系长度特征。[结果]土壤抗蚀性强弱表现为马尾松林大于桑树林。表层0—10cm范围内,桑树林地土壤根系小于马尾松土壤根系,土壤的抗蚀性随着土层深度的增加而减小;桑树林和马尾松林土壤根系主要分布在0—30cm层次内,而且1mm的根系长度由表层向深层递减,土壤平均孔径随着深度的增加而减小,而比表面积随着深度的增加而增大;在0—40cm深度马尾松各层次孔径分布呈分层现象,而桑树林各层次土壤孔径分布差异不大。土壤孔隙度和土壤孔径越大,土壤抗蚀性越强,而土壤颗粒比表面积越大土壤抗蚀性越小;通过SPSS分析得到桑树林地土壤抗蚀性与土壤根系质量在0.01水平上显著相关,马尾松土壤平均孔径与土壤根系质量在0.05水平上显著相关。[结论]降雨时,由于马尾松林地地表覆盖均匀,坡面产生壤中流下渗,土壤20cm以下分化明显,不易透水,导致下坡壤中流蓄满流出地表带出土壤颗粒。而桑树林地原为耕地无地表覆盖,人为翻种活动频繁,导致土壤层次性质相似,表层土壤颗粒流失严重。     

Effects of contact angle on fingered flow during non-ponding infiltration into dry sand layers

Abstract

Gravity-driven fingered flow may readily occur in dry sand layers with small capillary force at the same order of magnitude as gravitational force. Capillary force is related to the contact angle. The present study examined the effects of contact angle on fingered flow development, finger size and fingertip velocity during non-ponding infiltration into dry sand layers. For contact angles of 48–87°, an induction zone always formed in the sand layer, and only one finger developed from the induction zone. Fingertip width reached a minimum value when the contact angle was approximately 70°, and the width and velocity of fingertips were negatively correlated. This finding suggests that a contact angle of approximately 70° has a physical significance for fingered flow to determine fingertip velocity and width. In addition, when the contact angle was 91°, the supplied water did not spontaneously penetrate the sand surface; instead, water drops built up on the surface and two fingers directly formed from the surface. This indicates that 90° is indeed the critical contact angle for water repellency and affects fingered flow development during non-ponding infiltration.