Feasibility of measuring moisture content of green sand by a low frequency multiprobe detector based on dielectric characteristics

Green sand is a mixture of silica sand,bentonite,water and coal powder,and other additives.Moisture content is an important index to characterize the properties of green sand.Based on the dielectric characteristics of green sand and transmission line theory,a method for rapidly measuring the moisture content of green sand by means of a low frequency multiprobe detector was proposed.A system was constructed,where six detectors with different arrangements and probes were designed.The experimental results showed that the voltage difference of transmission line increases with the increasing frequency before 29 MHz while decreases after 35 MHz.A voltage difference platform occurs in the range of 29-35 MHz,which is suitable for measuring the moisture content due to its insensitivity to frequency.The electric field intensity gradually decreases with the increase of the probe depth,and the intensity of central probe is always greater than that of the edge probe.When the distance of the probe away from the sand sample surface is 80 mm,the electric field intensity of the edge probe is found to be very weak.The optimal excitation frequency for measuring the moisture content of green sand is 29-33 MHz.The optimal detector is the one with one center probe and three edge probes,and their lengths are 80 mm and 60 mm,respectively.The distance between the center and edge probes is 25 mm,and the diameter of probes is 5 mm.Taking the voltage difference of transmission line,bentonite content,coal powder content and compactability as parameters of the input layer,and the moisture content as a parameter of the output layer,a three-layer BP artificial neural network model for predicting the moisture content of green sand was constructed according to the experimental results at 33 MHz.The prediction error of the model is not higher than 3.3% when the moisture content of green sand is within the range of 3wt.%-7wt.%.

Influence of salinity and moisture on the threshold shear velocity of saline sand in the Qarhan Desert, Qaidam Basin of China: A wind tunnel experiment

Determination of the threshold shear velocity is essential for predicting sand transport,dust release and desertification.In this study,a wind tunnel experiment was conducted to evaluate the influence of salinity and moisture on the threshold shear velocity of saline sand.Saline sand samples(mean particle size of 164.50–186.08μm and the total silt,clay and salt content of 0.80%–8.25%)were collected from three saline sand dunes(one barchan dune and two linear dunes)in the Qarhan Desert,Qaidam Basin of China.Original saline sand samples were placed in two experimental trays for wet and dry processing to simulate deliquescence and desiccation,respectively.Surface moisture content ranging from 0.30% to 1.90% was generated by the steam method so that the saline sand can absorb water in a saturated water vapor environment.The motion of sand particles was determined by the observers with a solid laser.The laser sheet(0.80 cm thick),which was emitted by the solid laser,horizontally covered the sand surface and was bound to the sand.Results show that the cohesion of saline sand results from a combination of salt and water.The threshold shear velocity increases exponentially with the increase in crust thickness for the linear sand dunes.There is a positive linear correlation between the original moisture content and relative threshold shear velocity.The threshold shear velocity of dewatered sand is greater than that of wet sand with the same original moisture content.Our results will provide valuable information about the sand transport of highly saline soil in the desert.

Impact of Moisture Variation on Some Foundry Properties of Fori Silica Sand

Moulding Sand for metal casting is usually sourced from either natural deposit or synthetic mix of refractory sand grain binder and moisture. Each of the mix constituent is important in determining the characteristics of sand. The binding agent is responsible for bendability thereby determining the size of voids within the sand grain, while moisture level determines the plasticity of the foundry sand. Tests using American Foundry Society (AFS) Standard were followed in carrying out the experiment on Fori sand deposit to determine its suitability for foundry use. The sand was collected from the river bank of Fori, in Fori Community, Maiduguri, Borno State. The experimental test equipment includes: laboratory sand mixer, sand rammer, universal strength testing machine, permeability-meter, oven, mouldability machine, and as well as quick moisture teller. The chemical composition of the materials was carried out using atomic absorption spectrophotometer (AAS) model PG990AFG. The silica content in the material sample is about 78.65%, and with the traces of other elements, such as CaO (1.07%), Fe2O3 (0.76%), Al2O3 (15.81%), MgO (1.01%), TiO2 (2.21%), K2O (3.87%), and Na2O (1.16%), respectively. These percentages are within acceptable limits. The results of the physical properties revealed that the sand sample has clay content of 15.32% which is above the standard range of 10% - 12% recommended for natural moulding sands required for producing good quality castings. Other foundry properties of Forinatural moulding sand conducted include “moisture content” in the following ranges of percentages, 7.6%, 6.5%, 5.8%, 4.2% and 2.9% with the corresponding value of green compressive strength of (43.95, 53.47, 69.56, 68.21 and 61.16 KN/m2), dry compressive strength (93.50, 96.52, 105.50, 146.50 and 152.49 KN/m2), and permeability No. of 340, 390, 410, 430 and 440 respectively. It is clear from the test that, the lower the moisture content, the higher the dry compressive strength of the materials. The refractoriness value of the materials is 1400 ℃. The results of the physical and other foundry properties carried out show that Forisilica sand is suitable for casting non-ferrous alloys like bronze, brass and aluminium, and cast iron.

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.

沙坡头自然保护区不同固沙技术生态效益监测评价

【目的】为了深入了解设置沙障后不同固沙条件下植被物种组成、多样性的变化规律。【方法】以扎设草方格、尼龙网格、草绳方格固沙的沙地植被恢复技术示范区为研究对象,分析不同固沙模式对土壤风蚀、水分和电导率以及草本植物群落组成的影响,总结不同固沙模式对沙地植被恢复区的土壤风蚀、水分和电导率及植物多样性指数的影响规律。【结果】结果表明,①从总风蚀速率来看,流动沙丘风沙活动最强,为0.15 cm·d^(-1),且以沉积为主;草方格沙丘风沙活动最弱,为0.04 cm·d^(-1);土壤风蚀的总风蚀速率较流动沙丘减小0.11 cm·d^(-1)。沙丘风蚀与沉积的净变化速率在草方格沙丘最小,为-0.04 cm·d^(-1);流动沙丘最为剧烈,为0.15 cm·d^(-1);土壤风蚀的净变化速率较流动沙丘减小0.19 cm·d^(-1)。②流动沙丘和尼龙网格沙丘在不同土层深度的土壤水分和电导率无明显变化(P>0.05);草绳方格沙丘土壤水分含量由大到小依次为表层、深60 cm、深40 cm(P<0.05),不同土层深度电导率差异不显著(P>0.05);草方格沙丘土壤电导率由大到小依次为表层、深60 cm、深40 cm(P<0.05),土层深度对水分含量的影响较小(P>0.05)。③不同固沙模式对多度和物种数无显著影响(P>0.05)。不同固沙模式中,草本植被多样性指数无显著差异(P>0.05),表现较为一致的趋势;草方格沙丘的香浓-威纳指数、均匀度指数、物种数均最高,分别为0.93、0.57和1.80。【结论】综合分析表明,草方格固沙模式下植被恢复效果较好,对土壤水分和电导率影响较小;草绳方格固沙对土壤水分和电导率的影响较大。建议在后续沙地生态修复时,以草方格固沙为主,草绳方格为辅。

沙漠腹地风积沙压实特性试验分析

塔克拉玛干沙漠腹地修建石油钻井平台地基,地基材料运距远且会破坏沙漠地区生态环境,考虑到因地制宜,采用沙漠地区丰富的风积沙资源作为地基填料,其压实特性是影响地基施工工艺及质量的关键因素。为了研究其压实特性,进行了标准重型击实实验、超重型击实试验。研究结果表明:该地区风积沙粒径主要分布在0.075~0.25mm之间,属于级配不良的细砂;风积沙的重型、超重型击实曲线均呈“双峰”型,在干燥状态及最佳含水率时均能达到最大干密度,室内风积沙击实试验推荐使用大击实筒;不同的击实方式会产生不同的试验结果,最大干密度应结合现场确定。

砂砾石料含水率快速检测技术的探析及应用

众所周知,面板堆石坝的大坝填筑施工质量控制是以密度控制为主。在传统的检测方法中,含水率的检测时间较长且对粗粒土含水率的试验没有准确、可靠的方法。因此,面对大坝填筑量大、施工节奏快的具体情况,含水率的快速检测成为解决这一问题的重要因素。阐述了通过试验研究分析得出的一套快速、准确、实用性强的含水率快速检测方法,并予以应用,取得了较好的效果,为大方量大坝填筑保证工程质量、加快工程进度提供了必要的保障。

Analysis of drying and saturating natural gypsum samples for mechanical testing

The stability of underground abandoned gypsum mines is dependent on the gypsum pillar's strength,and most abandoned mines are in a fully saturated condition. Moisture affects the strength of gypsum and is therefore commonly measured when testing rock strength. For most rocks, this is a simple task of weighing the rock's mass before and after oven-heating at a specified temperature and duration. For natural gypsum, however, this is not a straightforward process. Heating natural gypsum can result in dehydration and transformation of gypsum to hemihydrate and anhydrite, thus changing the physical characteristics of the gypsum such as its particle density which in turn affects the moisture content and strength measurements. To prevent transformation when determining the moisture content of gypsum,the American Society for Testing Materials(ASTM) recommends lowering the drying temperature from 110℃ to 60℃ . To investigate the temperature at which gypsum transforms to hemihydrate, we used a helium pycnometer to measure the particle densities of gypsum, hemihydrate and anhydrite. In this research, we suggest that a higher drying temperature of 80℃ can be used for drying gypsum without transforming gypsum to hemihydrate. Further, preparing saturated samples for mechanical testing,which is required in stability analyses of abandoned mines, is challenging due to the dissolution of gypsum when placed in water. To address this problem, we investigated the following methods to saturate gypsum cores taking into account the solubility of gypsum:(1) water immersion,(2) vacuum saturation, and(3) improved vacuum saturation. The research indicates that all the three methods are acceptable but they should be conducted using a saturated gypsum-water solution to minimize dissolution. Further, the research found that the improved vacuum saturation method saturated the test samples within 24 h, while duration of 30 h was required for the other two methods.

干密度与含水率对标准砂抗剪强度的影响研究

抗剪强度是土的重要力学性质之一,是决定工程稳定性的关键因素。为研究砂土的强度特性,选取标准砂为试验材料,设计不同含水率与干密度水平的直剪试验,明确干密度与含水率对标准砂应力-应变曲线的影响,揭示其对标准砂抗剪强度特性的影响规律。研究结果表明:标准砂试样达到相同应变所需的应力随着标准砂的干密度及试验法向应力的增加而增加、随着标准砂含水率的升高而减少。在干密度为1.45cm^(3)与含水率为20%和25%的直剪试验中标准砂的应力应变曲线呈现出应变软化的特点,进一步分析表明标准砂的应力-应变曲线随着试样干密度增加、法向应力减小呈现出由硬化型应变向软化型应变转换的趋势。标准砂的抗剪强度随着干密度的增大而增大,随着含水率的增大而降低,其抗剪强度主要来源于材料颗粒之间的内摩擦角。在控制含水率不变的试验中内摩擦角随着干密度的增加依次增加0.54°,2.17°,1.99°和0.21°,呈现出平缓-陡峭-平缓的上升趋势;在控制干密度不变的试验中内摩擦角由含水率每降低1%降低0.5°降低至含水率每降低1%降低0.3°,随着含水率的升高呈现出陡峭-平缓的降低趋势。研究结果可以为与砂土相关工程的防灾预警等研究提供参考。

珊瑚砂界限干密度确定方法的比较研究

界限干密度(包含最大及最小干密度)是影响砂土力学性质的重要参数,将国标规范中干密度测定方法应用于岛礁珊瑚砂时,该类砂在干密度测定过程中产生了不可忽略的颗粒破碎,使得测定结果严重失真。分别采用中国(GB)、美国(ASTM)、日本(JIS)三国的相关规范,开展了针对珊瑚砂的界限干密度测定方法的比较研究;并与ISO标准砂的测定结果进行对比,进而提出适合于珊瑚砂干密度测定的建议方法。研究结果表明:对于不同粒径的珊瑚砂与标准砂,3种规范最小干密度测定结果为:ρ_(d min)^(JIS)<ρ _(d min)^(GB)<ρ _(d min)^(ASTM);最大干密度测定结果为:ρ_(d max)^(JIS)<ρ _(d max)^(GB)<ρ _(d max)^(ASTM)。珊瑚砂与标准砂在3种规范中干密度差异性大小△ρ_(d)随粒径变化规律存在显著的区别。随着含水率的增大,珊瑚砂的最大最小干密度均为:ρ_(d)^(JIS)<ρ _(d)^(GB)<ρ _(d)^(ASTM);不同规范间干密度差异性大小随含水率的增加先增大后基本保持不变。中国规范在干密度测定过程中的颗粒破碎远大于美国规范和日本规范。综合来看,美国规范所采用的干密度测定方法具有砂样状态定义清晰、操作简单、适用粒径范围广、界限干密度测定结果理想、颗粒破碎量少且干密度测定结果离散性小等优点,因而是一种适合珊瑚砂界限干密度测定的方法。

乌兰布和沙漠固沙梭梭林生长季土壤水分动态研究

土壤水分是干旱沙区荒漠植被生长发育的主要限制因子,为了解乌兰布和沙漠固沙梭梭林地的土壤水分动态变化特征,采用烘干法于2021年4—9月对梭梭林生长季土壤水分进行测定。结果表明,梭梭林地0—20 cm土壤含水量0.23%~2.13%,为浅层干沙层;20—80 cm土壤含水量0.36%~3.59%,为中层剧烈变化层;80—120 cm土壤含水量0.45%~1.63%,为深层稳定层。土壤含水量的月变化显示在4月处于土壤水分消耗较弱阶段;5—8月处于土壤水分消耗旺盛阶段;9月处于土壤水分缓慢恢复稳定阶段。土壤水分与土壤水势之间存在明显的对数函数关系(R~2均大于0.514 2)。综上所述,梭梭林地土壤水分垂直分布分层特征明显,时间上变异程度高于空间,具有较强的时间变异性,对该区人工植被建设具有重要意义。

塔克拉玛干沙漠腹地风积沙力学特性试验研究

为探究塔克拉玛干沙漠腹地风积沙作为地基土的物理力学特性,对该地风积沙进行了含水率、颗粒粒径、标准击实及直接剪切等物理力学试验。试验表明:该地区表层风积沙天然含水率为0.55%,距地表1 m深处含水率为1.59%;粒径范围主要分布在0.075~0.250 mm范围内,为级配不良的细砂;击实曲线表明该风积沙最佳含水率为19.63%时,在干燥状态和最佳含水率状态都可达到最大干密度1.65 g·cm^(-3);含水率和干密度的变化对风积沙抗剪强度有显著影响;干燥状态下风积沙的抗剪指标内摩擦角为32°。

影响三乙胺冷芯盒树脂砂强度的因素及应对措施

介绍了三乙胺冷芯盒树脂砂在冷芯盒射芯工艺、树脂加入量与三乙胺吹气时间为固定因素的情况下,原砂含泥量和含水量,制芯时的空气湿度和温度,芯砂可使用时间等因素的变化对强度性能的影响。分析总结出了南方地区冷芯盒树脂砂使用过程中的强度变化趋势曲线,确保冷芯盒制芯过程的质量控制及效率提升。最终制芯效率由280台/天提升到了320台/天,效率提升了15%。

白沙蒿种子萌发特性的研究II.环境因素的影响

白沙蒿 (Artemisia sphaerocephala Krasch.)是中国西北部沙漠的流动及固定沙丘上广泛分布的优势种灌木。白沙蒿种子为需光种子 ,种子在光下萌发而在黑暗中受到抑制。种子萌发的适宜温度为 2 5℃ ,在 10℃和 30℃萌发速率和萌发率都很低 ,萌发在 5℃受到抑制。种子在沙中被埋越深 ,其萌发速率和萌发率就越低。在沙平面下2 cm或更深层沙土下出苗率为零。但是 ,当将种子上层沙土移走 ,只保留 0 .5 cm沙土覆盖种子 ,这些种子的萌发率达到原先就位于沙土下 0 .5 cm的种子的萌发率 ,但是后者的萌发速率较高。土壤水分含量越高 ,从 1.7%到14.7% ,其萌发就越快。土壤水分含量从 19.4%起 ,种子的萌发受到了延迟 。

腾格里沙漠宁夏中卫沙层含水量研究

为了揭示腾格里沙漠地区沙层含水量、水分存在形式、运移和水分平衡等问题,对该沙漠东南部不同沙丘进行了含水量研究。结果显示,腾格里沙漠沙层含水量空间变化大,沙丘中、上部含水量低,下部与洼地含水量高。毛管水层指示毛管水上升高度一般为60cm左右,毛管水层平均含水量为14.9%。由于研究区相对降水量偏多,沙层水分存在饱和重力水、毛管水、高含量薄膜水和低含量薄膜水等多种形式,在毛管水层之上的沙层水分一般均为薄膜水,5%左右的高含量薄膜水的存在是该区沙层水分含量的突出特点。沙层中薄膜水带的上、中、下部均有含水量较高的层段,表明该区大气降水经蒸发、蒸腾之后,仍有剩余的水分向下入渗,并成为地下水的补给来源。

毛乌素沙地沙丘土壤含水量特点——兼论老固定沙地上油蒿衰退原因

土壤表面干沙层在冬春少雨季节较厚 ,流动沙地的又明显地大于固定沙地的。流动沙地地表干沙层以下的土壤含水量一般大于同深度固定沙地的 ,特别是在根系密集分布的土层。冬季或早春土壤含水量比较低 ,雨季的明显较高 ,雨季结束后 ,土层中的水分在重力的作用下会向深层运动 ,导致根系层土壤含水量下降。在植物生长季 ,缺少降雨时 ,固定沙地的土壤含水量会因植物的蒸腾消耗而变得很低 (1%～ 2 % ) ,而流动沙地的不受或受此影响很小。对土层持水能力的分析表明 ,土壤结构影响降水的有效性。固定沙地相对粘重的表土层影响降雨对灌木根系层土壤水分的补充。大于 1mm的降雨对流动沙地土壤水分的补给就有效果 ,但小于 5 mm的降雨基本上会被固定沙地的表土层吸收 ,对根系层土壤水分的补给效果不大。一般的小雨就有利于根系分布较浅的草本植物的生长 ,而只有较大的降雨才能有效地补给灌木根系层的土壤水分。然而 ,在固定沙地大暴雨还会因发生地表径流而降低其补给土壤水分的有效性。由此可知 ,固定沙地土壤结构对根系分布较深的灌木和半灌木的生长不利 ,而有利于其庇护下的草本植物的生长 ,并促使固定沙地油蒿群落在封闭的条件下向气候顶极的本氏针茅草原的演替。

库布齐沙漠含水率对风沙运动影响的风洞模拟

采用室内分析和风洞模拟试验的方法,研究了不同风速下库布齐沙漠沙丘沙含水率对粗糙度、风速廓线和风沙流结构变化的影响。根据风洞实际动力情况,确定试验进口风速为6,8,10,12,14,16m/s;除干沙外,人工配制了含水率为0.25%,0.5%,1.0%,1.5%,2.0%,2.5%6组不同湿度的沙样,分别开展了风洞模拟试验。结果表明,地表粗糙度随着风速的增加而增大,但随湿度的增加整体呈减小趋势;试验所包含的湿度范围内,其风速廓线均随高度呈对数分布,随风速的增大,风速廓线的对数规律越好,风速梯度逐渐减小;湿度越大输沙率随风速增加的绝对量变小,但相对量有所增加;随着湿度的增加输沙率呈整体下降趋势;不同湿度输沙率都出现随高度增加而减少的趋势,当湿度达到2.5%时,不管任何高度风蚀过程几乎停止;干沙输沙量80%集中于近地表5cm内,但随着湿度增加,5cm以上输沙率所占比重呈增加趋势,当湿度介于0.25%~1.5%时,地表5~8cm之间输沙量占总输沙率的30%以上。说明在地表含水率较高的库布齐沙漠,采用格状沙障等增加地表粗糙度的机械防沙措施能收到比西部沙漠和戈壁地区更为理想的效果,而且采用固沙措施的高度也应高于干沙地区。

二连浩特地区土壤湿度变化特征及其与沙尘暴关系的初步研究

利用内蒙古自治区中部二连浩特地区2001年4月-2004年4月土壤湿度的逐时观测资料,初步分析了二连浩特地区土壤湿度的变化特征;结合相应的地面气象资料,探讨了土壤湿度与沙尘天气之间的关系。结果表明,二连浩特地区土壤湿度具有1年为周期的变化,每年土壤湿度的峰值出现在降水较多的湿季,土壤湿度与沙尘暴发生次数呈负相关,土壤湿度对该地区沙尘暴的发生有重要影响。

低覆盖度行带式固沙林带间土壤水分动态特征

通过对低覆盖度（15%~30%）行带式赤峰杨固沙林不同部位降雨量和土壤含水量的定位观测,探讨了行带式分布格局下固沙林不同部位的土壤水分特征和时空动态变化。结果表明,在行带式这种特殊的分布格局下,在垂直于林带的方向上,土壤水分分布总体上表现出明显的区域差别。根据土壤水分空间分布规律发现,低覆盖度行带式分布格局的固沙林林带内存在水分利用带和入渗补给带;在0-40cm深度水分利用带和入渗补给带土壤水分含量受降雨量影响上下波动剧烈,但入渗补给带和带间6m处水分利用带土壤水分含量对于降雨的响应较18m处利用带更加敏感;40-160cm深度,土壤水分含量受降雨量和林带蒸腾耗水影响,入渗补给带对水分利用带的土壤水分具有一定的补给调控作用。

含湿沙导热系数的测试与实验研究

采用Hot Disk热常数分析仪(TPS 2500)对不同含湿率沙子的有效导热系数进行测量和实验研究。研究发现,非饱和含湿堆积沙的有效导热系数随含湿率的增加而增大。低含湿率(体积含湿率低于25%)情况下,堆积沙的有效导热系数难以准确测得,其主要原因是测试过程中,由于加热影响,贴近探头附近的水分因蒸发扩散而逐渐减少,探头周围试样构成不能保持恒定,导致测试环境持续发生变化。