Experimental research on the mixed sand ratio and initial dry density of weathered sand improved expansive soil free load swelling rate

In this paper, through the indoor free load swelling rate test, expansive soil in a section of a first- class highway reconstruction project in Yichang City was studied. It emphatically analyzed the interrelations among free load swelling rate, non-load time, the proportion of mixed sand and initial dry density. Experimen- tal studies have shown that： Free load swelling deformation is mainly divided into three stages of rapid expan- sion, slow expansion and final stability; when the initial dry density is constant, free load swelling rate of the weathered sand modified soil will reduce rapidly before they slow down with the increase of sand proportion, and weathered sand modified soil free load swelling rate is not sensitive to the large amount of sand mixed; in the same mixed sand ratio, weathered sand modified soil free load swelling rate increases rapidly with the in- crease of initial dry density, there is a good linear correlation between them. To take appropriate control of the initial dry density during the expansive soil subgrade construction helps to reduce its swelling deformation and ensures the stability of the embankment.

Effects of free iron oxyhydrates and soil organic matter on copper sorption-desorption behavior by size fractions of aggregates from two paddy soils

Effects of free iron oxyhydrates （Fed） and soil organic matter （SOM） on copper （Cu^2＋） sorption-desorption behavior by size fractions of aggregates from two typical paddy soils （Ferric-Accumulic Stagnic Anthrosol （Soil H） and Gleyic Stagnic Anthrosol （Soil W）） were investigated with and without treatments of dithionite-citrate-bicarbonate and of H2O2. The size fractions of aggregates were obtained from the undisturbed bulk topsoil using a low energy ultrasonic dispersion procedure. Experiments of equilibrium sorption and subsequent desorption were conducted at soil water ratio of 1：20, 25℃. For Soil H, Cu^2＋ sorption capacity of the DCB-treated size fractions was decreased by 5.9% for fine sand fraction, by 40.4% for coarse sand fraction, in comparison to 2.9% for the bnlk sample. However, Cu^2＋ sorption capacities of the H2O2-treated fractions were decreased by over 80% for the coarse sand fraction and by 15% for the clay-sized fraction in comparison to 88% for bulk soil. For Soil W, Cu^2＋ sorption capacity of the DCB-treated size fraction was decreased by 30% for the coarse sand fraction and by over 75% for silt sand fraction in comparison to 44.5% for the bulk sample. Cu^2＋ sorption capacities of the H2O2-treated fractions were decreased by only 2.0% for the coarse sand fraction and by 15% for the fine sand fraction in comparison to by 3.4% for bulk soil. However, Cu^2＋ desorption rates were increased much in H2O2-treated samples by over 80% except the clay-sized fraction （only 9.5%） for Soil H. While removal of SOM with H2O2 tendend to increase the desorption rate, DCB- and H2O2-treatments caused decrease in Cu^2＋ retention capacity of size fractions, Particularly, there hardly remained Cu^2＋ retention capacity by size fractions from Soil H after H2O2 treatment except for clay-sized fraction. These findings supported again the dominance of the coarse sand fraction in sorption of metals and the preference of absorbed metals bound to SOM in differently stabilized status among the size fractions. Thus, enrichment and turnover of SOM in paddy soils may have great effects on metal retention and chemical mobility in paddy soils.

Measurement of free heavy metal ion concentrations in soils using Donnan membrane technique

In natural systems heavy metals are present in very low concentrations (less than micro-molar), so precise measurement of the free metal ions is difficult. Recently, a new method has been developed called the Donnan membrane technique (DMT). Several heavy metals could be measured simultaneously using this method. Furthermore, all the metals did not interfere with each other, and the balance between the measured system and the surrounding condition could not be disturbed. Improvements were made according to the internal condition. The free heavy metal ion concentrations were measured in different systems using the improved method, and satisfied results have been obtained.

Free cupric ions in contaminated agricultural soils around a copper mine in eastern Nanjing City, China

To determine the environmental free metal ion activity was a recent hot issue. A method to measure low-level free cupric ion activity in soil solution extracted with 0.01 mol/L KNO3 was developed by using cupric ion-selective electrode （ISE） and calibrating with Cu-buffer solution. Three copper buffers including iminodiacetic acid （IDA）, ethylenediamine （EN）, and glycine （Gly） were compared for calibrating the Cu-ISE curves in the range of free cupric ions （pCu^2＋） 7-13. The Cu-EN buffer showed the best electrode response and thus was applied as the calibration buffer. The pCu^2＋ of 39 contaminated agricultural soils around a copper mine was measured, ranging from 5.03 to 9.20. Most Cu in the soil solutions was found to be complexed with dissolved soil organic matters, averaging 98.1%. The proportion of free Cu^2＋ ions in the soil solutions decreased with the increasing of solution pH. Soluble Cu and free Cu^2＋ ions concentrations were analyzed by multiple linear regressions to evaluate the effects of soil properties on metal levels and speciation. The results showed that soil solution pH was the most significant factor influencing pCu^2＋ （with R^2 value of 0.76）, while not important for the soluble Cu concentration.

Evaluation on Heavy Metal Pollution of Soil in Pollution-free Agricultural Product Bases in Guangxi

Using data of 6 pollution-free agricultural product bases in Guangxi Zhuang Autonomous Region,this paper analyzed content of heavy metals,including arsenic(As),mercury(Hg),lead(Pb),cadmium(Cd),and chromium(Cr) in soil.After Pb,Cd,Cr,Hg and As content in soil is determined,it evaluated the pollution of soil using single factor pollution index method and Nemerow synthetic pollution index method in combination with evaluation standard of heavy metals in soil and grading standard for soil pollution.Analysis results indicate that As,Hg,Pb,Cd,Cr content is different in pollution-free agricultural product bases,but all conform to related standards and there is no standard exceeding problem.It is concluded that the quality of soil in pollution-free agricultural product bases is excellent,not polluted and completely meet requirements of evaluation standards,and suitable for developing pollution-free agricultural products.

Four years of free-air CO_2 enrichment enhance soil C concentrations in a Chinese wheat field

Elevated atmospheric CO2 can influence soil C dynamics in agroecosystems. The effects of free-air CO2 enrichment （FACE） and N fertilization on soil organic C （Corg）, dissolved organic C （DOC）, microbial biomass C （Cmic） and soil basal respiration （SBR） were investigated in a Chinese wheat field after expose to elevated CO2 for four full years. The results indicated that elevated CO2 has stimulative effects on soil C concentrations regardless of N fertilization. Following the elevated CO2, the concentrations of Corg and SBR were increased at wheat jointing stage, and those of DOC and Cmic were enhanced obviously across the wheat jointing stage and the fallow period after wheat harvest. On the other hand, N fertilization did not significantly affect the content of soil C. Significant correlations were found among DOC, Cmic, and SBR in this study.

Effect of red mud on the mobility of heavy metals in mining-contaminated soils

The mobility of Cu2+, Zn2+, Ni2+, and Cd2+ in soils treated with red mud was experimentally studied to explore the feasibility of remediation of smelter-contaminated soils. Red mud samples were collected with the Bayer process (BRM) and confederate process (CRM) in the Aluminous Plant of Guizhou Province. Two farmed soil samples were collected from the Niujiaotang mining area, Guizhou Province, Southwest China. One sample was weakly polluted by fly ash; and the other was polluted severely by waste water from the smelter. For evaluating the potential of remediation, the concentrations of free metal ions and the distributions of metals in the soil were determined. The concentrations of free metal ions were measured by using the Donnan Membrane Technique, and the contributions of soil sorbents to the heavy metals adsorptions were calculated with Equilibrium Calculation of Speciation and Transport (ECOSAT). BRM reduced the concentrations of free metal ions in two kinds of soils, while CRM only favored the decrease of the concentrations of free metal ions in seriously contaminated soils. The experimental data also showed a tendency that the concentrations of free metal ions decreased proportionally with the amount of added red mud, which resulted from the increasing adsorption of heavy metal ions in the form of metal ion hydroxides.

Adaptive element free Galerkin method applied to analysis of earthquake induced liquefaction

An automatically adaptive element free method is presented to analyze the seismic response of liquefiable soils. The method is based on the element free Galerkin method （EFGM） and the fission procedure that is part of h-refinement, indicated by error estimation. In the proposed method, a posteriori error estimate procedure that depends on the energy norm of stress and the T-Belytschko （TB） stress recovery scheme is incorporated. The effective cyclic elasto-plastic constitutive model is used to describe the nonlinear behavior of the saturated soil. The governing equations are established by u-p formulation. The proposed method can effectively avoid the volumetric locking due to large deformation that usually occurs in numerical computations using the finite element method （FEM）. The efficiency of the proposed method is demonstrated by evaluating the seismic response of an embankment and comparing it to results obtained through FEM. It is shown that the proposed method provides an accurate seismic analysis of saturated soil that includes the effects of liquefaction .

增效型无土相仿生油基钻井液技术的研究与应用

针对深井超深井钻井过程中钻遇高温高压、井壁失稳及井下复杂情况的难题,基于仿生学、超分子化学以及岩石表面润湿性理论,通过优选仿生增效剂、仿生提切剂及仿生降滤失剂,配套相关处理剂,最终形成了一套适用于深井、超深井地层钻探的增效型无土相仿生油基钻井液体系。研究发现,建立的增效型无土相仿生油基钻井液体系可抗220℃高温,配制密度为2.4 g/cm^(3),破乳电压大于400 V,高温高压滤失量为3.2 mL,人造岩心在该体系中220℃下老化后的抗压强度达到7.1 MPa,平均渗透率恢复值为93.9%。现场应用情况表明,体系流变性能稳定,平均机械钻速比邻井提高16%,平均井径扩大率仅为1.25%,可有效解决深井超深井钻井过程中出现的井壁失稳难题,为我国深井超深井的钻探提供了技术保障。

Studies on Heavy Metal Pollution in Soil-Plant System:A Review

Heavy metal pollution in soil-plant system is of major environmental concern on a world scale and in China in particular with the rapid development of industry. The heavy metal pollution status in soil-plant system in China, the research progress on the bioavailability of heavy metals (affecting factors, extraction methods, free-ion activity model, adsorption model, multivariate regression model, Q-I relationship, and compound pollution), and soil remediation are reviewed in the paper. Future research and monitoring is also discussed.

An Effective Method for Free Vibration of Plate on Elastic Half Space

The vibration analysis of a plate on an elastic foundation is an important problem in engineering. It is the interaction of a plate with the three-dimensional half space and the plate is usually loaded from both the upper and lower surfaces. The contact pressure from the soil can not be predefined. According to Lamb's solution for a single oscillating force acting on a point on the surface of an elastic half space, and the relevant approximation formulae, a relation between the local pressure and the deflection of the plate has been proposed. Based on this analysis, the reaction of the soil can be represented as the deformation of the plate. Therefore, the plate can be separated from the soil and only needs to be divided by a number of elements in the analysis. The following procedure is the same as the standard finite element method. This is a semi-analytical and semi-numerical method. It has been applied to the dynamic analysis of circular or rectangular plates on the elastic half space, at low or high frequency vibration, and on rigid, soft or flexible foundations. The results show that this method is versatile and highly accurate.

土壤游离铁CS AAS测定方法的验证

为提高游离铁的检测效率,本研究对游离铁(Fed)的测定(DCB法)提取液在原子吸收光谱仪上的检测进行验证。使用CS AAS上机时对特征参数包括标准曲线、检出限、检出下限、精密度、准确度进行验证及确认。确定线性范围为0~7.0 mg/L,非线性拟合回归方程相关系数0.999 8、检出限0.005 3 g/kg、检出下限0.021 g/kg。普通土壤样品检测精密度相对相差小于10%,相对标准偏差小于1.9%,满足方法中平行测定质量控制要求和《化学分析方法验证确认和内部质量控制要求》。对高、中、低3个有证标准物质进行6次测定,相对误差小于10%,满足正确度的要求,上机测试数据稳定可靠。

皖西南富硒土壤分布及富硒农产品调查

本文以土地质量地球化学调查数据为基础,分析了皖西南富硒土壤的分布、无公害绿色富硒土壤、无公害富硒农产品产地适宜区、绿色富硒农产品产地适宜区及绿色富硒食品等情况。结果表明,富硒土壤面积占总评价面积的4.97%,主要分布在CS、SH、GZ、TZS和TF等乡镇。无公害绿色富硒土壤面积约占富硒土壤总量的85.57%,富硒土壤达到无公害农产品产地环境标准和绿色食品产地环境标准的面积一致。无公害富硒农产品产地适宜区占评价区总面积的4.25%。绿色富硒食品产地适宜区占评价区总面积的4.24%,其中AA级适宜区占1.80%,A级适宜区占1.78%。富硒土壤主要为自然背景成因,且富硒土壤具有有机质含量较高的特征,推测富硒土壤成因为吸附型富硒。查明了特色农产品绿色富硒水稻、茶叶和栝楼生产区。该结果为研究区天然富硒土地资源开发利用提供参考。

Microstructural, Chemical and Mineralogical Analyses for Understanding the Geotechnical Properties of Clayey Soils

This paper presents a study research in the laboratory of three clayey soils from the depression of the Lama, a tropical climate area where disorders appear on construction and roads. Samples were tested to establish the relationship between their mineralogy and their geotechnical properties. On the three clayey soils, analyses were performed to characterize the macroscopic behavior (physical tests, free swelling test and compressibility tests) and the microstructural, chemical and mineralogical characterizations by thermal analysis, chemical analysis, X-Ray diffraction, Scanning Electron Microscopy observations complementary X-ray EDS analyses. At first glance, the results of physical and compressibility tests appear not to be consistent with the free swelling test results. Indeed, these results highlighted differences in the behaviors of the samples because the swelling potential revealed by the results of physical and compressibility test does not follow the same trend as the one given by the free swelling test result. The main clay minerals in the studied clayey soils varied from fibrous clays (palygorskite) to best-known clays such as smectite and kaolinite. Microstructural, chemical and mineralogical analyses allowed to understand and explain the different trends obtained by the different types of geotechnical characterization tests of studied clayey soils.

Visible and Near-Infrared Spectroscopy with Multi-Parameters Optimization of Savitzky-Golay Smoothing Applied to Rapid Analysis of Soil Cr Content of Pearl River Delta

Using visible and near-infrared (Vis-NIR) spectroscopy combined with partial least squares (PLS) regression, the rapid reagent-free analysis model for chromium (Cr) content in tideland reclamation soil in the Pearl River Delta, China was established. Based on Savitzky-Golay (SG) smoothing and PLS regression, a multi-parameters optimization platform (SG-PLS) covering 264 modes was constructed to select the appropriately spectral preprocessing mode. The optimal SG-PLS model was determined according to the prediction effect. The selected optimal parameters d, p, m and LV were 2, 6, 23 and 8, respectively. Using the validation samples that were not involved in modeling, the root mean square error (SEPV), relative root mean square error (R-SEPV) and correlation coefficients (RP, V) of prediction were 11.66 mg·kg-1, 10.7% and 0.722, respectively. The results indicated that the feasibility of using Vis-NIR spectroscopy combined with SG-PLS method to analyze soil Cr content. The constructed multi-parameters optimization platform with SG-PLS is expected to be applied to a wider field of analysis. The rapid detection method has important application values to large-scale agricultural production.

水稻秸秆与园林基质混配用作无土草毯生产技术研究

为了筛选适宜的无土草毯基质配方,降低无土草毯生产成本,以水稻秸秆与园林基质为材料,将其按不同的比例混合,并添加2种不同来源的菌剂进行有氧发酵,配制成不同的基质处理,对不同混配基质的理化性状、植物毒性和种植草毯的坪用性状等指标进行比较分析。结果表明:添加北京金宝贝菌剂进行发酵且水稻秸秆与园林基质体积比为6∶4的处理基质物理性状较理想,有机质含量显著高于其他处理,且其养分含量较均衡,重金属含量符合NY/T 525-2021有机肥标准要求,其所建植的草毯坪用性状显著高于其他处理。在本试验条件下,该配方基质比较适合用于无土草毯栽培。

游离氧化铁对花岗岩残积土崩解和抗剪强度的影响

为分析游离氧化铁对花岗岩残积土的力学性质的影响,以桂东南地区花岗岩残积土为研究对象,通过连二亚硫酸钠-柠檬酸钠-碳酸氢钠(DCB法)溶液去除花岗岩残积土中的游离氧化铁,并制备了不同游离氧化铁含量的重塑土样。研究表明:游离氧化铁含量的增加显著提高了花岗岩残积土的抗剪强度,同时显著降低了其水稳定性和抗崩解性能。基于试验结果,建立了游离氧化铁含量与崩解特性及抗剪强度之间的拟合关系,有效反映了土体性质随游离氧化铁含量的变化趋势。

干湿循环下花岗岩残积土胶结物溶蚀-微结构演化规律与力学行为

花岗岩残积土中的游离氧化铁粒间胶结作用使其具有高结构性和水敏性.因此,在干湿循环过程中,粒间胶结氧化物被溶蚀,残积土表现出结构崩解重组和复杂的剪切变形特性.为进一步研究干湿循环过程中花岗岩残积土中游离氧化铁溶蚀造成的土体组构变化及其对力学性能弱化的影响,进行一系列的宏微观试验以揭示不同干湿循环次数(0、1、2、4)下残积土的复杂力学特性.研究结果表明,随着干湿循环次数的增加,花岗岩残积土的应力-应变关系将由弱应变硬化型逐渐转变为应变软化状态.微观分析表明游离氧化铁会促使黏土颗粒胶结形成团聚体,随着干湿循环的进行其含量逐渐降低最终趋于稳定.此外,原状残积土粒度分布(PSD)曲线呈现明显的双峰,然后在干湿循环或去除氧化铁后转变为单峰曲线.反复干湿循环会削弱残积土的胶结结构特性,进而导致土体出现明显的软化特征.在剪切过程中,残积土首先表现出剪切收缩特性,随后出现明显的扩张趋势.随着干湿循环次数增加,残积土的有效黏聚力逐渐减小,但有效内摩擦角呈现逐渐增加的趋势.干湿循环过程中花岗岩残积土复杂的力学性能特点是不可逆的体积收缩和胶粒含量的变化以及微裂缝发展之间的耦合效应.

DCB溶液作用下膨胀土裂隙面力学特性试验研究

为了探究水化学作用下膨胀土裂隙面力学特性的变化,选取引江济淮工程菜子湖C003标段膨胀土,通过特定的制样方式赋予试样预设裂隙面,采用连二亚硫酸钠-柠檬酸钠-碳酸氢钠(DCB)溶液对含裂隙土样进行淋滤,并对淋滤后的试样进行抗剪强度试验研究,探究裂隙面强度变化与淋滤时间的关系,揭示淋滤后膨胀土裂隙面强度变化的微观机理。试验结果表明:DCB溶液沿着预设裂隙面和试样内部淋滤不同天数后,试样形貌特征出现了不同的变化;裂隙面抗剪强度降低速率随着淋滤时间的增加先变快后变慢,在淋滤28 d后裂隙面抗剪强度指标下降明显,黏聚力和内摩擦角分别下降51.5%和45.9%;对淋滤后试样表面灰绿土样和直剪试验后剪切面土样进行微细观研究发现,淋滤后灰绿土和剪切面Fe_(2)O_(3)含量下降明显,且黏土矿物衍射峰强度有一定程度的升高。微观机理分析可知,DCB溶液通过氧化还原作用对土中游离氧化铁进行去除,使试样外观形貌出现较大变化,破坏了土中大的团聚体与颗粒之间的黏结力,从而导致土体力学特性劣化。

火焰原子吸收光谱法测定土壤中游离铁含量

土壤游离铁是成土母质风化、迁移转化的产物,其形态和活化、老化程度能够反映成土过程和成土环境,可以直接反映土壤的形成环境、形成过程和气候变化。因此,准确测定土壤中的游离铁含量具有重要的现实意义。目前采用紫外分光光度法测定游离铁实验流程长,需要将高价铁还原为低价铁,加之需要显色时间24h,耗费时间长,检测效率较低。本文采用火焰原子吸收光谱法(FAAS)测定土壤中的游离铁含量,系统研究了实验条件对游离铁测定的影响,通过优化样品测定过程中碳酸氢钠的用量、反应温度、反应时间以及清洗次数,确定了称样量为0.5g,加入柠檬酸钠溶液20mL和碳酸氢钠溶液2mL,反应温度75~80℃,反应时间15~30min,再用饱和氯化钠溶液和2mL 1mol/L氯化钠溶液清洗各一次为最佳实验条件。经验证,该方法检出限(3σ)为0.05g/kg,定量限为0.20g/kg,标准曲线线性相关系数为0.9995,方法精密度(RSD,n=6)为1.95%~3.76%,标准样品测定误差小于5%,符合土壤调查样品分析测试要求,可推广应用于土壤调查中土壤和沉积物样品分析。