湿软土壤的剪切应力—剪切速度—时间关系

从位错理论出发导出了湿软土壤的剪切应力－剪切应变－时间关系。理论分析和试验结果表明土壤剪切应力与剪切速度成幂函数关系；与其本身可能抵抗的最大剪应力相比的相对剪应力水只与剪切位移有关而与剪切速度无关。     

湿软土壤剪切应力—剪切速度—时间关系及其应用(第1报)——湿软土壤剪切变形机理探析

为了探讨湿软土壤的剪切应力—剪切位移关系,对湿软土壤的剪切变形机制进行了分析。分析结果表明,由于土壤内部颗粒排列的不规则性和缺陷的存在使得其抗剪能力大大降低。可借助位错理论的某些方法来阐述湿软土壤的剪切变形机理。     

湿软土壤剪切应力—剪切速度—时间关系及其应用（第1报）：湿软土壤剪…

为了探讨湿软土壤的剪切应力－剪切位移关系，对湿软土壤的剪切变形机制进行了分析。分析结果表明，由于土壤内部颗粒排列的不规则性和缺陷的存在使得其抗剪能力大大降低。可借助位错理论的某些方法来阐述湿软土壤的剪切变形机理。     

湿软土壤剪切应力—剪切速度—时间关系及其应用(第3报)——湿软土壤上履带板的推力计算

为了合理地预测湿软地上履带行走装置的推进力,对履带板的推力计算模型进行了修正。修正后的计算模型考虑了土壤受剪速度对其剪切应力的影响。实验结果表明履带板的推力介于考虑和不考虑履剌效应的两个理论值之间。     

湿软土壤剪切应力—剪切速度—时间关系及其应用(第4报)——水田链桨式驱动装置推力计算

为寻求合适的水田驱动装置及其推力的预测方法,阐述了链桨式驱动装置的工作原理并在将土壤作为流变体的情况下导出了其推力的计算公式。试验表明,导出的式子与实测结果吻合良好。     

粘性土壤剪切强度与容重和含水量之间关系的研究

本文在Mitchell等人关于土壤剪切强度唯一性研究的基础上,利用热力学第二定律作指导,由试验和分析建立了剪切强度与热扩散系数之间关系。据此关系,综合De Vries和佐滕用三相比表达热扩散系数的方程式,得到一个四参数剪切强度-干容重-含水量模型。对于一种粘土在各种容重和含水量下进行了三轴剪切试验,本模型拟合实测数据的精度(用相关系数表示)皆在0.9以上。     

三峡库区紫色土渗流—应力的耦合关系

[目的] 研究三峡库区紫色土在渗流与应力耦合作用下的渗透特性和抗剪强度特性,深入探究紫色土应力—渗流的耦合关系,为农业工程、边坡工程、水土保持等实际工程应用提供理论参考。[方法] 以三峡库区紫色土为研究对象,借助SLB-1A型应力应变控制式三轴剪切渗透试验仪,分析多因素耦合对紫色土抗剪强度特性和渗透性的变化。[结果] 含水率对三峡库区紫色土的黏聚力c与内摩擦角φ的影响程度不同,并在含水率为11%处取得峰值,内摩擦角随含水率增大而减小,二者变化趋势符合线性变化的特征;紫色土渗透性的变化在不同含水率梯度间存在较大的差异性,且含水率在11%～13%之间时差异性相对显著;以渗透压等于40 kPa为临界值,紫色土的渗透性降低形式不同;主应力差控制值越大,不同含水率紫色土的渗透性降低越显著。[结论] 渗透—剪切作用下,含水率和围压极大影响了紫色土的抗剪强度,其黏聚力在含水率11%处取得峰值,黏聚力和内摩擦角的变化符合线性变化;相同条件下,主应力差控制值越大,不同含水率紫色土的渗透性降低越显著,主应力差的贡献率高于含水率。各因素对影响紫色土渗透性的贡献率由高到低依次为：渗透压＞主应力差＞围压＞含水率。     

草本植物根系增强土壤抗剪切强度的量化研究

通过对黄土高原丘陵沟壑区山西省河曲县砖窑沟流域内4种有代表性的草本植物进行野外剪切测试和模型预测,证实和量化了草本植物根系增强土壤抗剪切强度的作用。试验表明,在0～20cm土层4种草本植物根系均可显著增加土壤抗剪切强度,其中紫花苜蓿根系对土壤抗剪切强度的增强作用最大,其增大土壤抗剪切强度值为15．33kPa;草木樨和紫花苜蓿根系在20～40cm土层也能明显增大土壤抗剪切强度。同时,对比分析了实测结果与模型预测值间的差异,认为根系增大土壤抗剪强度的真实值应介于实测值和预测值之间。研究结果也表明这4种草本植物根系均具有较高的抗拉强度,且根系的抗拉强度与直径间存在显著幂函数负相关关系。这些研究对黄土区预测和评估草本植物根系的固土护坡作用,以及水土保持植物的选择及优化组合,更有效地发挥植物根系生物软措施的固土潜能具有重要现实指导意义。     

滑板土壤间充气层的理论计算及其试验验证

采用气幕法可以有效地减少滑板在湿软土壤上的滑行阻力,其减阻效果取决于滑板土壤间充气层的压力、厚度和宽度等状态参数。文中提出了一种数学模型,从理论上预测了充气层的诸状态参数,并对理论预测结果进行了试验验证。理论计算和试验测量结果均表明:离充气孔越远,充气层厚度越薄;而随着流量的增加,充气层厚度和压力也增加。     

土壤—固体表面粘附行为的热力学分析

依据界面热力学原理对土壤—固体表面粘附行为进行了分析。土壤粘附强度主要由毛细管作用力和界面水膜粘滞力构成,固体表面性质对其产生影响。本文还讨论了土壤动物体表特征,其体表憎水性、体表液的低粘滞性和亚宏观到微观层次上的非光滑结构是重要的表面特征。     

Shear strength of surface soil as affected by soil bulk density and soil water content

This paper proposes a new method to measure the soil strength parameters at soil surface in order to explain the processes of soil erosion and sealing formation. To simulate the interlocks between aggregates or particles within top 2 mm of the soil, a piece of sandpaper (30 particles cm⁻²) was stuck on the bottom face of a plastic box of diameter of 6.8 cm with stiffening glue and used as shear media. The soil strength for the soils from sandy loam to clayey loam was measured with penetrometer and the new shear device at soil surface at different bulk density and soil water content. The normal stresses of 2, 5, 8, 10 and 20 hPa were applied for the new shear device. The results indicated that significant effect of bulk density on soil strength was detected in most cases though the difference in bulk density was small, ranging from 0.01 to 0.09 g cm⁻³. It was also indicated that the measurement with the new shear device at soil surface was reproducible. The changes in soil shear strength parameters due to changes in bulk density and soil moisture were explainable with the Mohr–Coulomb’s failure equation and the principles of the effective stress for the unsaturated soils. The implications of the method were later discussed.     

紫色页岩发育土壤的颗粒特性及其对抗剪强度的作用机制

土体发生破坏最开始往往是从内部的土壤颗粒破坏开始,而抗剪强度是反映土体抵抗剪切破坏能力的重要指标。本文以紫色页岩发育的坡耕地土壤为研究对象,通过测定土样颗粒组成以及不同含水率和垂向压力下的抗剪强度,研究页岩发育的土壤颗粒特性及其对抗剪强度的作用机制。结果表明从坡顶至坡脚,土壤颗粒组成与其母岩颗粒组成具有显著相关性;土壤中0.25 mm颗粒累计含量在995.65～998.62 g/kg之间,其中以0.25～2 mm岩石碎屑存在的土壤颗粒含量为439.80～510.40 g/kg,以0.25～2 mm团聚体存在的土壤颗粒含量为6.01～80.50 g/kg,随着位置高程的降低,土壤中岩石碎屑和团聚体的含量并没有显著变化。在含水率从7%增加到25%的过程中,土壤水分与内摩擦角呈负相关关系且对内摩擦角的影响随着高程的降低缓慢减小,而对黏聚力的影响是随着含水率的增加单一坡位黏聚力呈现先增加后减少的趋势,但是随高程降低变化并不明显。因此,在紫色页岩发育的土壤颗粒组成中存在大量2 mm的岩石碎屑,这些大量致密坚硬的岩石碎屑提高土壤抗剪强度同时减弱了抗剪强度的水敏性。     

干湿循环对崩岗不同层次土体无侧限抗压强度的影响

针对发育于花岗岩出露区的崩岗土体易受干湿循环影响导致大量崩壁失稳等问题,通过开展一系列室内无侧限抗压强度试验,研究崩岗不同层次土体在干湿循环作用下无侧限抗压强度的变化规律,并且建立了在崩岗不同层次土体深度比和干湿循环次数共同影响下的无侧限抗压强度模型。结果表明:表土层、红土层、斑纹层、碎屑层在第1次干湿循环后无侧限抗压强度衰减幅度最大,分别为26%,15%,40%和49%;在第2~4次干湿循环后无侧限抗压强度衰减幅度逐渐减小;在第5次干湿循环后无侧限抗压强度基本保持不变;随着干湿循环次数的增加,崩岗不同层次土体无侧限抗压强度总体表现为表土层红土层斑纹层碎屑层;在不同干湿循环次数下,崩岗不同层次土体的应力—应变曲线总体上呈应变软化型且应变为2%时达到峰值,但红土层在3次干湿循环时的应力—应变关系曲线局部波动性较强;无侧限抗压强度模型中预测值与实测值之间具有显著(R2=0.91)的相关关系,该模型在预测干湿循环对通城地区崩岗不同层次土体无侧限抗压强度影响中具有较高的应用价值。     

Kinetics of K Desorption from Soils in a Constant Electric Field (Electro-Ultrafiltration) and Its Application

Kdesorption from soils in a constant electric field (field strength:44.5Vcm^-1) by means of electro-ultrafil-tration (EUF) followed second-order kinetics and could be described by the equation dd/dt=k(D-d)2. From theequation, such kinetic parameters relating to K desorption from soils as the maximum desorbable quantity D, quantity of K desorbed within 40 minutes d40, initial desorption rate Vo, desorption rate constant k and half-time t1/2 could be calculated. An expression which describes the relationships between the kinetic parameters on the one hand and the responses of barley to fertilizer-K in the field experiments in different sites and the potassium-supplying power of soils on the other was established. Vo, D and d40 were significantly correlated with barley relative yield, K uptake by barley and the content of soil available potassium. The rate constants of K desorption varied between 4.42×10^-4-1.80×10^-3kg mg^-1 min^-1 and highly correlated with the relative yield of barley.     

Occurrence of Polycyclic Musks in Sewage Sludge and their Behaviour in Soils and Plants. Part 2: Investigation of Polycyclic Musks in Soils and Plants (9 pp)

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Part 2: Investigation of Polycyclic Musks in Soils and PlantsPart 1: Behaviour of Polycyclic Musks in Sewage Sludge of Different Treatment Plants in Summer and Winter

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Preamble. In Part 1 of the study, screening tests were performed to investigate the occurrence of PCM in sewage sludges. For a preliminary risk assessment, further information is needed about their behaviour in the terrestrial environment. Hence Part 2 examined the adsorption of PCMs to soil, their dissipation and leaching in soil and their uptake in plants.

Goal, Scope and Background

Polycyclic Musks (PCMs) enter the terrestrial environment via the use of sewage sludge as fertilizer. After entry into soil, they can be taken up by plants or move into the groundwater body. However, until now no overall risk assessment for polycyclic musks is available. For a preliminary risk assessment further information is needed about their behaviour in the soil environment. Therefore, Part 2 of the study (Part 1, see J Soils Sediments, OnlineFirst ) examined the adsorption of PCMs to soil, their dissipation and leaching in soil and their uptake by plants.

Methods

Analytical methods for the determination of HHCB and AHTN in soil and plant samples were developed and applied. The adsorption/desorption studies were performed according to OECD guideline 106 and draft guideline 121 using three soils. Dissipation (aerobic degradation) was examined according to BBA guideline 4-1 in three soils over a test period of 37 weeks under controlled conditions. Leaching experiments in soil columns were performed using columns of 14 cm Ø and 30 cm filling height for a test period of 48 hours. Finally the uptake of PCMs by lettuce and carrots was studied in laboratory and outdoor experiments.

Results

The adsorption/desorption studies resulted in Koc values between 4200 and 7900 for HHCB and between 4800 and 13600 for AHTN showing strong sorption to the soils investigated. The dissipation of the PCMs occurred very slowly with elimination rates after 37 weeks of approx. 50% and 25% for HHCB and AHTN, respectively. The leaching experiments showed leaching rates of < 0.001% for HHCB and AHTN during a test period of 48 hours. The slight leaching is presumably due to ‘preferential flow'. The transfer factors (ratio of concentrations in the plant to concentrations in the soil ) for HHCB in lettuce and carrot leaves determined in plant uptake experiments were as low as 0.003. For HHCB in carrot roots however high transfer factors of 0.095 for a humic and 0.48 for a loamy soil were obtained. The high uptake may be caused by partitioning of the HHCB into the essential oil cells of the carrot roots.

Discussion

The polycyclic musk compounds HHCB and AHTN showed high adsorption to soil. A desorption phenomenon occurred after three desorption steps. High adsorption influences the slow degradation kinetic. Comparable investigations into the degradation behaviour show the same results, whereas other authors observed a faster degradation. We assume a dependency on microbial consortia, which can vary as a function of the substrate and adaptation of the microbial population. Leaching tests were carried out in our study, but not by other studies. The results reflect the adsorption into the soil matrix.

Conclusions

The results show that PCMs are widespread contaminants in sewage sludge and should be considered in a risk assessment as potential contaminants of sewage sludge destined for agricultural use. When applied to soil they may remain in the upper soil layers due to their high sorption, low degradability and low leaching behaviour. Uptake by some plants like carrot roots may be relevant.

Recommendations and Perspective

. This study examined the adsorption of PCMs to soil, their dissipation and leaching in soil and their uptake into plants. For a qualitative risk assessment more data on adsorption /desorption, and degradation in soils under different soil conditions needs to be generated. Also, further studies have to be carried out to gain a better understanding of plant uptake of PCMs, especially HHCB and AHTN.

     

郑州市城市土壤砷含量的分布特征及其成因探讨

在对郑州市城市土壤采样分析的基础上,探讨了土壤中As的含量、分布、成因及其与人类活动的关系.结果表明,郑州市城市土壤表层土壤的平均As含量为7.67 mg/kg,变幅为3.25～10.00 mg/kg,未达到污染的水平;但城市土壤中As含量普遍高于郊区对照样,城市土壤高As值区位于老居民区、文教区和商业区.郑州市城市土壤As含量自表层向下没有一定的分布规律,且与土壤理化性质之间没有相关关系;其主要与人类活动强烈干扰有关,是典型的人为源重金属元素.城市土壤外源性As的输入主要是工业"三废"和市民日常生活中所丢弃的含As废物.     

Aggregate Stability and Its Relationship with Some ChemicalProperties of Red Soils in Subtropical China

The stability of aggregates in the surface soil is crucial to soil erosion and runoff generation. Thus, to understand the stability and the breakdown mechanisms of soil aggregates as well as the relationship between aggregate stability and selected soil chemical properties, such as different forms of Fe and A1 oxides, organic matter, CEC and clay content, the aggregates of slightly and severely eroded red soils derived from Quaternary red clay in subtropical China were analyzed using the routine wet sieving and the Le Bissonnais methods. The results indicated that the aggregates of the severely eroded soils were more stable than those of the slightly eroded soils. Different aggregate breakdown mechanisms resulted in different particle size distribution. The slaking from entrapped air in aggregates severely destroyed the soil aggregates,especially in the slightly eroded soils. Meanwhile, mechanical breakdown and microcracking had little effect on the aggregates compared to slaking. The fragments resulting from slaking were mainly microaggregates that increased in size with increasing clay content. The main fragment size of the slightly eroded soils was 1.0-0.2 mm, while for the severely eroded soils it was 5.0-2.0 mm and 1.0-0.5 mm. Overall, more than 20% of the fragments were smaller than 0.2 mm.In addition, aggregate stability was positively and often significantly correlated with Fed, Ald, Feo and clay content, but significantly and negatively correlated to SOC.