A New Approach for Smoothing Soil Grain Size Curve Determined by Hydrometer

In hydrometer analysis for soil grain size distribution, usually, the grains passing sieve No. 200 (<0.074 mm) are used. However, the hydrometer results occasionally give diameters greater than 0.074 mm. This event causes a mismatch in the curve of grain size distribution obtained from sieving and hydrometer methods. Hence, a new approach is proposed for smoothing soil grain size curve determined by hydrometer using Excel-2007 with simple statistical methods. The treatments show that in case of large sizes, there are big differences between the values of soil grain diameters smoothed by Excel-2007 in comparison and the values measured by references. These differences generally decrease with decreasing soil grain size diameters. The statistical treatments also divulge whether the hydrometer results are accurate or not. Furthermore, a general equation has been derived to estimate values of K factor, which is used for calculating the grain diameters in hydrometer analysis. The equation can be applied for any specific gravity of soils and for wide range temperatures.

Experimental study on grain size and soluble salt of saline soil in western Jilin Province, China

Western Jilin Province is a typical seasonal frost region, and is also one of the severest salinization areas of China. In this study, we aim to examine the saline soil in Da＇an and Wukesong areas, western Jilin Province, and mainly analyze the granulometric composition and distribution of salt in soil profiles. Four sampling sites, two in Da＇an and two in Wukesong respectively, are chosen for study. The granulometric composition, especially silt and clay content change in different sites and soil depths are analyzed. Analysis of total and components of soluble salt shows that the surface soil is weak carbonate saline, in which the main cation is Na＋ and the main anion is HCO3-. The total amount of soluble salt presents a decreasing tendency with increasing depth. The comprehensive analysis ofgranulometric composition and soluble salt shows that the clay content and soluble salt content present similar variation tendency with an increase of depth.

The Soil Moisture and Grain Size Characteristics of Micro-area: A Case Study of Minqin Oasis- Desert Ecotone

To elaborate soil moisture and grain size characteristics of 3 typical micro-areas in Minqin oasis-desert ecotone,samples were collected in runoff generation area and accumulated area using soil profile and multi-point sampling method,for soil moisture and physicochemical property analysis. Research results that( i) water accumulation trace of accumulated area is significant and the vegetation coverage is larger than the runoff generation area. The crust development in clay sand barrier + Haloxylon ammodendron forest accumulated is better than runoff generation area,while the situation is contrary in Nitraria tangutorum sand dune lowland and clay flat land.( ii) Moisture of accumulated area in fixed Nitraria tangutorum sand inter-dune lowland is better than the runoff generation area; the moisture of accumulated area in clay flat land topsoil is significantly better than the runoff generation area,while the topsoil moisture of clay sand barrier + Haloxylon ammodendron forest is better in the runoff generation area than in the accumulated area.( iii) Soil moisture of accumulated area in 3 types of micro-areas is in the range of 20- 40 cm; the fixed Nitraria tangutorum sand inter-dune lowland is better than clay flat land and clay sand barrier + Haloxylon ammodendron forest,while the lowest moisture of corresponding runoff generation area is basically consistent with the depth.( iv) The topsoil clay and powder content in accumulated area of fixed Nitraria tangutorum sand inter-dune lowland is lower than the runoff generation area,while the fine sand content in deep layer of runoff generation area is greater than the accumulated area; soil in two areas of clay flat land mainly consists of coarse and fine sand,and clay particles are better in runoff generation area than in accumulated area. Soil in the clay sand barrier + Haloxylon ammodendron forest is mainly coarse sand and the structure is single. In sum,through adjusting allocation of rainfall,micro-areas influence soil moisture and grain size distribution,and further influence spatial- temporal distribution of vegetation in sand micro-areas.

Grain Size and Major Oxide Analyses of Selected Anthill Soils from Winneba Area, Ghana

Termites build their habitat in the form of anthills or termitaria or termite mounds which are characterised by soil of clayey texture. This paper investigated the relative grain size from the base, middle and near the peak of three anthills located 20 km west of Winneba near the Apam-Winneba highway in Ghana and also correlated their elemental compositions. The results showed significant grain size gradation of soils which range from 2O3 (22.18 - 28.88), MnO (0.08 - 0.09), and K2O (0.4 - 0.61). However, as K2O decreased with height on anthill, SiO2, total FeO and Al2O3 increased. Probably soils used to construct these anthills were derived from different rock types and/or the termites were selective in the use of soils rich in silica or iron oxide.

Distribution and characteristics of gravelly soil liquefaction in the Wenchuan M_s 8.0 earthquake

In this paper,a distribution map of gravelly soil liquefaction that was caused by the Wenchuan M8.0 earthquake in China is proposed based on a detailed field investigation and an analysis of geological soil profiles. The geological background of the earthquake disaster region is summarized by compiling geological cross sections and borehole logs. Meanwhile,four typical liquefied sites were selected to conduct sample drillings,dynamic penetration tests (DPT),and shear wave velocity tests,to understand the features of liquefied gravelly soil. One hundred and eighteen (118) liquefied sites were investigated shortly after the earthquake. The field investigation showed:(1) sandboils and waterspouts occurred extensively,involving thousands of miles of farmland,120 villages,eight schools and five factories,which caused damage to some rural houses,schools,manufacturing facilities and wells,etc.; (2) the Chengdu plain is covered by a gravelly soil layer with a thickness of 0 m to 541 m according to the geological cross sections; (3) there were 80 gravelly soil liquefied sites in the Chengdu plain,shaped as five belt areas that varied from 20 km to 40 km in length,and about ten gravelly soil liquefied sites distributed within Mianyang area; and (4) the grain sizes of the sampled soil were relative larger than the ejected soil on the ground,thus the type of liquefied soil cannot be determined by the ejected soil. The gravelly soil liquefied sites are helpful in enriching the global database of gravelly soil liquefaction and developing a corresponding evaluation method in further research efforts.

甘肃民勤人工梭梭林土壤粒度特征研究

梭梭(Haloxylon ammodendron)作为石羊河流域人工固沙林的主体,对维持区域生态环境稳定具有重要作用。通过对民勤不同年代营造的人工梭梭林0~100 cm层土壤粒度特征进行分析,研究梭梭造林后植被恢复过程中土壤粒度组成、分形维数及与土壤理化性质的作用关系。结果表明,1)民勤人工梭梭林土壤以细砂(100~250μm)为主(33.08%~65.83%),其次是中砂(15.42%~40.79%)。20世纪70年代营造的梭梭林土壤黏粒、粉粒及极细砂高于其他年代梭梭林。人工梭梭林对土壤粒度的影响主要在表层(0~10 cm)区域,较深土层变异较小。2)民勤人工梭梭林风沙土质地较粗,分选系数介于较好和较差之间,偏度为近对称-正偏度,峰值为中等-尖窄,分形维数变化范围为1.400~2.166。3)分形维数与黏粒、粉粒、极细砂含量呈极显著正相关(P<0.01),与细砂、中砂含量分别呈极显著(P<0.01)、显著(P<0.05)负相关。民勤人工梭梭林土壤粒度的形成受到土壤有机质、全N、速效P及pH的影响较大。研究结果为民勤人工林建设、沙化土地治理以及生态恢复提供理论依据。

Environmental and Mineralogical Studies of the Sabkhas Soil at Ismailia—Suez Roadbed, Southern of Suez Canal District, Egypt

Eight surface sabkha soils samples were collected from Ismailia—Suez roadbed, southwestern of Suez Canal district. Sedimentological and mineralogical analyses were conducted using grain size;X-ray diffraction and Scanning Electron Microscopy (SEM). Grain size analysis indicates high contents of fine sand and mud as well as presence of salts. X-ray diffraction;Scanning Electron Microscopy (SEM) and EDAX tool clarified that the sabkha soils are enriched by quartz, sulfate minerals (gypsum, anhydrite), carbonate minerals (calcite-dolomite-aragonite), chlorides (halite and bischofite), and clay minerals. The results elucidate that the appearance of sabkha deposits and their distribution in the study area are controlled mainly by the content of water soluble salts through parent materials;ground water table;subsurface structural;and physiographic features for instance surface relief or topography;and human activity.

砂质黏性紫色土粒组缺失对降低持水特性的影响

紫色土结构松散、具高生产性,但具有较弱的抗侵蚀能力,侵蚀后表现出土壤干密度减小、细颗粒流失严重等现象,影响其持水特性。为探讨紫色土降雨侵蚀后土壤持水特性的变化,该研究选取砂质黏性紫色土在降雨条件下最易变化的3组粒组(>0.250~0.500、>0.075~0.250、0~0.075 mm),开展广义吸力范围内粒组缺失的土-水特征曲线(soil-water characteristic curve,SWCC)试验,分析粒组缺失对砂质黏性紫色土持水特性的影响。结果表明:1)粒组缺失会降低土体持水特性,在边界效应区和过渡区最为明显,残余区影响较小。缺失粒组质量分数与进气值和残余含水率呈反比;2)使用粒径参数(限制粒径、平均粒径、中值粒径、有效粒径)表征土体级配状况,建立土体级配曲线与SWCC特征值的关系,发现除有效粒径,其余参数均与进气值和残余值呈线性反比关系;3)使用Fredlund-Xing模型对不同方法所得数据进行拟合,发现使用单一试验方法所得数据结果拟合优度较高,但SWCC明显偏离其余试验数据点。提出获得准确的紫色土全吸力SWCC仅需确定吸力最大值,并引入3种评价指标进行验证,拟合结果表明,此方法可有效缩短SWCC试验周期,为SWCC在三峡库区紫色土地区的工程运用提供了可靠的思路。

基于双分形级配模型参数的粗粒土渗透系数计算公式

粗粒土在自然界中分布广泛且在工程中应用普遍。渗透性是粗粒土的重要性质,对于同种粗粒土,因颗粒级配与孔隙特征几乎决定其渗透性,原则上其渗透系数应该可基于颗粒级配和孔隙特征参量计算得到。采用基于分形理论建立的双分形级配模型对粗粒土的连续级配、间断级配进行定量描述,以确定该级配模型的适用性并获得级配模型参数。在此基础上,基于双分形级配模型参数和Kozeny-Carman公式构造出包含级配参量及孔隙率的渗透系数计算公式。在论述了计算公式中各项物理意义后,基于现有文献的实测数据验证该计算公式的有效性。结果表明,双分形级配模型能准确唯一地定量描述粗粒土的颗粒级配;建立的含颗粒级配参量和孔隙率的粗粒土渗透系数计算公式是合理的,该公式适用于计算连续和间断级配粗粒土的渗透系数。

缩尺效应对粗颗粒土静止侧压力系数影响规律试验

准确把握粗颗粒土静止侧压力系数K_(0)对分析及设计土石坝等岩土工程具有十分重要的作用。由于缩尺效应的存在,粗颗粒土室内K_(0)试验结果往往无法正确反映其真实值。本文利用自行研制的大型K_(0)测试仪对某砂卵砾石料及堆石料进行大量试验,以研究分析缩尺效应对粗颗粒土K_(0)影响规律,找出消除缩尺效应影响的方法。通过改变试样颗粒的最大粒径d_(M)、缩尺方法、初始相对密实度D_(r0)等初始条件,设置24组试样,利用大型K_(0)测试仪对各组试样进行直剪试验,定量研究d_(M) 、缩尺方法和D_(r0)对粗粒土K_(0)的影响规律,并探讨以室内试验数据推求现场粗粒土K_(0),从而消除缩尺效应的方法。结果表明:D_(r0)及缩尺方法不变时,粗颗粒土K_(0)随着d_(M) 的增加而显著减小,因此,缩尺效应会导致粗颗粒土K_(0)显著增高,且缩尺后土料d_(M) 越小,其K_(0)受影响程度越高;D_(r0)及d_(M)相同时,缩尺方法对粗颗粒土K_(0)有一定影响,采用等量替代法缩尺后,试样K_(0)值增加最小,因此,采用等量替代法缩尺可减小缩尺效应对粗颗粒土K_(0)的影响;相比d_(M) ,D_(r0)对粗粒土K_(0)的影响更为显著,D_(r0)越大的土样,d_(M)对粗粒土K_(0)影响更明显。基于砂卵砾石料K_(0)试验结果及前人的研究,建立根据室内试验结果反推现场粗颗粒土料K_(0)的公式,以消除缩尺效应对粗颗粒土K_(0)的影响。利用堆石料K_(0)试验结果验证了该经验公式的准确性及适用性。

拉萨河流域不同植被类型坡面砾石形态与分布特征

坡面砾石的分布特征显著影响着地表土壤侵蚀及水文过程,而目前针对高寒区坡面砾石形态与分布特征的研究较为薄弱。为此,在西藏拉萨河流域选择9个典型坡面的山坡及其下堆积坡,将其按山坡—堆积坡的植被类型分为草—草坡面(A)、灌草—草坡面(B)和灌草—灌草坡面(C)3类,并对各坡面样点进行现场拍照采样,利用ImageJ软件获取砾石粒径、圆度、形状比率以及覆盖度,分析不同类型坡面砾石的粒度组成、形态特征以及覆盖度,研究坡面砾石的形态与分布特征。结果表明:(1)A类坡面山坡砾石平均粒径显著大于堆积坡,B类坡面山坡和堆积坡砾石平均粒径无显著性差异,C类坡面山坡砾石平均粒径显著小于堆积坡;同一类坡面之间的砾石粒度组成存在差异。(2)整体上A,B,C这3类坡面的山坡和堆积坡砾石圆度和形状比率无显著性差异。(3)A类坡面山坡砾石覆盖度大于堆积坡,B类坡面山坡和堆积坡砾石覆盖度相差不大,C类坡面山坡砾石覆盖度小于堆积坡;同一类坡面之间的砾石覆盖度大小存在差异。(4)同一坡面山坡和堆积坡砾石平均粒径及覆盖度主要受坡度的影响,而同一类坡面之间的砾石粒度组成及覆盖度大小因受植被、气候、岩性、海拔等的影响也存在差异。研究结果可为研究青藏高原土壤侵蚀与水文过程提供理论依据,为该区域水土流失治理工作提供科学支撑。

粗粒土抗剪强度的缩尺效应规律试验研究

抗剪强度是评价土体稳定性的重要指标,研究缩尺效应对粗粒土抗剪强度的影响,对高土石坝工程土体强度估算有重要的理论意义和应用价值。根据前人的研究,颗粒最大粒径d_(max)和级配结构两部分变化是导致缩尺后试样存在缩尺效应的主要原因,其中级配结构可由级配面积S作为特征参数表示。通过改变试样的d_(max)和S,设计了24组不同级配试样,利用大型直剪仪对各组试样进行直剪试验,从而定量研究颗粒最大粒径和级配结构对粗粒土抗剪强度的影响规律。研究结果表明:粗粒土的抗剪强度指标黏聚力c和内摩擦角φ均表现出随着d_(max)增大而增大的规律,且c和φ均与d_(max)呈对数函数关系;黏聚力c和内摩擦角φ随着S的减小而增大,到达某一特定值后呈略微减小的趋势,并根据相应试验数据分别建立c和φ与S的关系式。最后,基于试验结果建立了考虑缩尺效应的粗粒土抗剪强度的预测模型,并用相关文献试验数据验证了该模型对不同类型粗粒土的适用性。

基于离散元的碎片尺寸随机的颗粒破碎模拟方法

依据天然堆石颗粒的破碎特性,构建了子颗粒粒径随机的碎片替换模式,即立方体替换模式.采用立方体替换模式可得到符合天然堆石颗粒破碎特性的子颗粒粒径分布.单轴压缩模拟试验表明,与子颗粒粒径固定的4球和18球替换模式相比,立方体替换模式能提高试样级配曲线的连续性,并改善中间粒径缺失的问题.对比不同子颗粒数量替换模式的模拟结果可知,立方体替换模式对应试样的接触数目和平均接触力分布符合替换模式子颗粒数量对分布的影响规律;剔除无接触和单接触颗粒后,3种替换模式的细观力学特性的变化规律一致,表明立方体替换模式可以用于模拟粗粒土的颗粒破碎.

鄱阳湖泗洲头湿地土壤粒度组成及其对有机碳的影响

为探究土壤质地对天然湿地土壤有机碳含量的影响,以鄱阳湖泗洲头湿地为研究对象,利用激光粒度分析仪测定苔草(Carex cinerascens)、南荻(Triarrhena lutarioriparia)、芦苇(Phragmites australis)、荻(Miscanthus sacchariflorus)和狗牙根(Cynodon dactylon)5种优势植被下的表层(0~20 cm)和下层(20~40 cm)土壤粒度组成,采用Folk-Ward公式计算土壤粒度参数,分析土壤粒度分布特征,利用结构方程模型(structural equation model,SEM)和Pearson相关性探讨土壤粒度组成与土壤有机碳的关系。结果表明,鄱阳湖泗洲头湿地土壤质地以粉黏土和砂壤土为主,分选性较差。粉黏土质地组成主要以粉粒(67.76%~79.28%)为主,平均粒径(Mz)为6.91Φ,粒度频率曲线为双峰或三峰分布;砂壤土质地组成主要以细砂(32.90%~56.55%)为主,Mz为3.00Φ,粒度频率曲线为单峰分布。粉黏土土壤有机碳含量为(10.52±3.86)g/kg,显著高于砂壤土土壤有机碳含量((1.67±1.66)g/kg)。土壤质地对土壤有机碳含量具有直接影响,黏粒、粉粒和砂粒均是影响土壤有机碳含量的重要影响因子。研究区黏粒与粉粒对土壤有机碳的固持能力显著高于砂粒,因此,对鄱阳湖湿地进行保护时应重视土壤质地对固碳的影响。

Grain-size features of a Miocene loess-soil sequence at Qinan: Implications on its origin

In this study, grain-size of 507 bulk samples from the QA-I Miocene loess-soil sequence at Qinan were analyzed, and the grain-size features are compared with those of typical Quaternary loess and soil samples, representative lacustrine and fluvial samples. The results indicate that the grain-size distribution pattern of the Miocene loess is essentially similar to that of Quaternary loess, but greatly differs from the lacustrine and fluvial sediments. Loess layers are regularly coarser than soil layers, indicating cyclical climate changes. Median grain-size along the 253.1 m sequence varies from 6 to 13 μm and the >63 μm fraction represents only 5.3% in maximum, 0.9% in average. Long-term grain-size variations are consistent with the loess accumulation rate at Qinan and with the eolian mass accumulation rate in the North Pacific. These features firmly indicate an eolian origin of the studied sequence, and also reveal a coeval changes between the long-term changes of eolian grain-size and continental aridity in the dust source regions.

Kinetic and thermodynamic studies on partitioning of polychlorinated biphenyls (PCBs) between aqueous solution and modeled individual soil particle grain sizes

The significance of soil mineral properties and secondary environmental conditions such as pH, temperature, ionic strength and time in the partitioning of eight selected polychlorinated biphenyl(PCB) congeners between aqueous solution and soil particles with different grain sizes was studied. The mineral properties of a model soil sample were determined, and Brunauer–Emmett–Teller(BET) adsorption–desorption isotherms were employed to observe the surface characteristics of the individual modeled soil particles.Batch adsorption experiments were conducted to determine the sorption of PCBs onto soil particles of different sizes. The results revealed that the sorption of PCB congeners onto the soil was dependent on the amount of soil organic matter, surface area, and pore size distribution of the various individual soil particles. Low pH favored the sorption of PCBs,with maximum sorption occurring between pH 6.5 and 7.5 with an equilibration period of 8 hr.Changes in the ionic strength were found to be less significant. Low temperature favored the sorption of PCBs onto the soil compared to high temperatures. Thermodynamic studies showed that the partition coefficient(K_d) decreased with increasing temperature, and negative and low values of ΔH° indicated an exothermic physisorption process. The data generated is critical and will help in further understanding remediation and cleanup strategies for polluted water.

荒漠光伏电站对地表土壤机械组成分布的影响

在光伏发电和荒漠治理有机融合的新形势下,为探明荒漠光伏电站对地表土壤机械组成分布的影响,以期给荒漠光伏电站生态的恢复和治理提供参考。以库布齐荒漠光伏电站为研究对象,对光伏阵列内电板不同位置以及裸沙区对照地表0~5 cm的土壤进行取样,通过Mastersizer3000型激光粒度分析仪测量土壤粒度组成,计算并分析了光伏电板不同位置(电板前沿、电板中间、电板后沿)的土壤粒度组成、土壤颗粒统计特征,以及粒度特征(平均粒径、偏差),对比了光伏电板不同位置土壤机械组成及其分布的差异。结果表明:(1)库布齐荒漠光伏电站中,土壤以中沙和细沙为主,光伏电板前沿的中沙体积百分含量最多,较裸沙区的中沙体积百分含量多27.76%,电板中间处细沙体积百分含量最多,较裸沙区的细沙体积百分含量多3.76%,由光伏电站外缘到内部呈现土壤颗粒细化趋势;(2)库布齐荒漠光伏电站中,电板不同位置极细沙的变异性最大,可达37.36%,而中沙的标准差最大,各粒级平均值均表现为细沙>中沙>极细沙;(3)光伏电板不同位置平均粒径差异较为明显,电板前沿处地表0~5 cm的沉积物的平均粒径范围在Ф1.8836~Ф2.0248,平均值为Ф1.9112,属于中沙范围,较裸沙区地表沉积物平均粒径差异显著,而电板中间和电板后沿处的平均粒径均属于细沙范围;(4)电板不同位置的偏差均在负偏范围内,电板中间的偏差较大,这也说明其偏差向对称性发展。光伏电站外缘中电板前沿处地表0~5 cm的土壤颗粒偏粗,而光伏电站内部电板中间处的地表呈现土壤颗粒细化趋势,故应在光伏电板前沿重点区域设置适当的防护措施,用来降低土壤颗粒粗化程度,防治土壤风蚀提高电站防风固沙能力,促进荒漠生态恢复。

嘉陵江流域紫色土区土壤磁化率和粒度对重金属污染的响应特征

【目的】嘉陵江流域紫色土区是长江上游重要的农业区,人为作用对土壤扰动较强,水土流失严重,探讨该区不同土地利用方式下土壤重金属污染现状及其对磁化率和粒度的影响,对长江上游生态环境保护具有重要意义。【方法】采集并测试了嘉陵江流域中段南充市城区和郊区不用土地利用方式下78个表层土壤的重金属元素(Cr、Ni、Cu、Zn、As、Cd、Pb和Mn)、磁化率和粒度组成,采用数理统计方法对这3个指标进行了相关性分析。【结果】研究区土壤质量磁化率与频率磁化率、粒度相关性不显著,有别于自然发育土壤和污染严重土壤,表明人为作用改变了土壤自然发育形成的物理性质,但土壤未受污染;土壤磁性颗粒主要受人类活动影响,表现为频率磁化率偏低;质量磁化率与主要重金属污染元素呈显著正相关,Pb、Cu和As是研究区主要的外源性输入物;土壤黏粒含量与Cr、Ni、Cu、Zn及As呈显著正相关,而与Cd呈显著负相关,粒度与Pb相关性不显著;土壤中Cd、Cr和Ni主要受控于自然因素,未受人为活动影响。【结论】土壤磁化率、粒度特征及其与重金属含量的相关性分析可初步判断土壤是否受到污染,并辨识主要重金属污染物。

Two categories of fractal models of rock and soil expressing volume and size-distribution of pores and grains

Based on the Sierpinski carpet and Menger sponge models, two categories of fractal models of rock and soil which are composed of the volume fractal model of pores, the volume fractal model of grains, pore-size or particle-size distribution fractal models are established and their relations are clarified in this paper. Through comparison and analysis, it is found that previous models can be unified by the two categories of fractal models, so the unified fractal models are formed. Experimental results presented by Katz indicate that the first category of fractal models can be used to express the fractal behavior of sandstone. A scanning electron microscope (SEM) will be used to study the microstructure of soft clay and it will be testified that the fractal behavior of soft clay suits the second category of fractal models.

考虑颗粒密度的细粒土分形特征研究

以广东地区两大水利工程项目的原状土为研究对象,针对细粒土颗粒结构的复杂性和不规则性,基于分形理论和数理统计,提出了考虑颗粒密度的细粒土质量分形维数模型,建立了细粒土质量分形维数预测方程,讨论了质量分形维数与宏观物理特性的关系。结果表明:考虑颗粒密度的质量分形维数模型具有更好的适用性;细粒土的质量分形维数与粉粒含量呈较强的负相关,与胶粒含量呈较强的正相关,以此建立的质量分形维数预测方程具有较好的预测效果,并初步确定了细粒土质量分形维数的变化区间为(2.674,2.921);仅用质量分形维数无法直接判断细粒土界限含水率的高低或可塑性的强弱。研究结果为今后细粒土的分形理论研究打下了基础。