Inhibition effect of swelling characteristics of expansive soil using cohesive non-swelling soil layer under unidirectional seepage

Cohesive non-swelling soil (CNS) cushion technology is widely used to solve swelling deformation problems in expansive soil areas. However, the swelling inhibition mechanism is still not fully understood. In this study, the inhibition effect on expansive soil using a CNS layer was studied by performing five types of laboratory model tests under unidirectional seepage. The results showed that CNS cushion technology produced a sound inhibition effect on the swelling characteristics of expansive soil. It was shown that the cations in the CNS layer moved downward and accumulated on the surface of solids and produced an electrical environment inside the expansive soil. In this process, the adsorbed hydrated cations participated in ion exchange with the expansive soil, leading to the modification effect on its swelling potential. Meanwhile, the adsorbed water membrane surrounding the expansive soil aggregates formed by the hydrated cations obstructed further adsorption of water molecules, which inhibited the swelling development of expansive soil. Therefore, the swelling inhibition mechanism can be attributed to three factors: (i) modification effect, (ii) electrical environment, and (iii) deadweight of the CNS layer. The combined contribution of modification effect and electrical environment can be considered as an electric charge effect, which mainly controls the swelling characteristics of expansive soil.     

Microplastics in soils: a review of possible sources,analytical methods and ecological impacts

Microplastics are emerging persistent pollutants that have been extensively detected in aqueous environments. Yet, scientists have little knowledge of microplastic pollution in soils. This study reviewed over 60 articles, with the following objectives: (i) to discuss sources and the global distribution of microplastics in soils; (ii) to evaluate current extraction techniques and analytical methods for microplastics in soils; and (iii) to comprehensively assess their adverse impacts on soils and soil organisms. Moreover, this review highlights the lack of research into microplastic contamination in soils as a significant knowledge gap. Research into the fate, sources and analytical techniques of soil microplastics and the interactions between soil organisms, soils and microplastics is essential in order to underpin management decisions aimed at safeguarding the ecological integrity of our soils. © 2020 Society of Chemical Industry     

Tertiary‐amine‐free,non‐planar,sulfone‐containing,tetrafunctional epoxy and its application as a high temperature matrix

Non‐amine‐derived tetrafunctional epoxies have several advantages over the amine‐derived N,N,N′,N′‐tetraglycidyl‐4,4′‐diaminodiphenyl methane (TGDDM) in high temperature applications. Although two non‐amine‐derived tetrafunctional epoxies were developed in our laboratory, further improvements in toughness using less loading amount is still desirable. Thus, a tertiary‐amine‐free, non‐planar and triphenylmethane‐containing tetrafunctional epoxy (STFE) with a sulfone spacer was synthesized. When it was mixed with diglycidyl ether of bisphenol A (DGEBA) and cured with 4,4′‐diaminodiphenylsulfone (DDS), both thermal and mechanical performances outperformed TGDDM. Moreover, STFE modified system shows the highest toughness (35.7 kJ m^–2) among three amine‐free and triphenylmethane‐containing epoxies at merely 5 wt% loading. Molecular simulation and thermomechanical analysis results suggest that the improved mechanical properties could be related to the geometry of the molecule and larger free volume. Despite a marginal drop in T_g, the thermal degradation temperature is better than that of TGDDM/DDS. In addition, the moisture resistance of STFE/DGEBA/DDS is much better than that of TGDDM/DDS. Thus, STFE modified DGEBA could be a potential replacement for TGDDM in some high temperature applications. © 2020 Society of Chemical Industry     

An effective method of bulk materials moisture measurement using capacitive sensors

When we speak about capacitance moisture meters for bulk materials we have to face with different values of dielectric permittivity for different bulk materials in dehydrated state, what causes a method error that can be named ‘type uncertainty’. Besides, different varieties of the same material have different values of dielectric permittivity, which depend from geographical origin, processing conditions etc. It can be hardly predicted automatically and type uncertainty can be compensated only in separate situations with the help of preliminary calibration. Main tasks of the research are to develop new comparison principle of moisture measurement with better accuracy due to effective compensation of physical, chemical and granulometric composition influence on the result of moisture measurement, develop new primary and secondary instrument transducers. Moisture sensor consists of four measuring capacitors. Two of them should be filled with a sample, which moisture content should be determined, and other pair of measuring capacitors should be filled with a same substance, but previously dehydrated. Mathematical models, developed to take into account granulometric composition of a bulk material were used to carry out a comparison analysis for three types of instrument measuring transducers. Obtained results proved that suggested principle of moisture measurement provides effective compensation of granulometric composition influence. Developed measuring principle had been experimentally tested what helped to confirm that it provides two times better compensation of different physical and chemical composition for different materials in comparison with the direct comparison method.     

土壤中石油污染物的脱附过程

文章中主要采用有机溶剂萃取法（OSE）对高浓度石油污染土壤进行修复，经过精馏操作，有效回收原油，建立脱附等温曲线，研究了石油污染物在土壤-有机溶剂两相间的迁移规律。     

天然土壤胶体对U(Ⅵ)迁移的影响

以石英砂为填充介质，采用动态柱实验方法研究了某中低放处置场地表土壤胶体对U(Ⅵ)在石英砂柱中迁移行为的影响，并结合静态批式实验探究了土壤胶体对U(Ⅵ)迁移的影响机制。结果表明，当U(Ⅵ)进样质量浓度从1.0 mg/L增大至5.0 mg/L时，U(Ⅵ)在石英砂柱中的穿透速率显著增大，且达到洗脱平衡时所需淋洗液的体积从250 PVs（孔隙体积）增大至400 PVs。与U(Ⅵ)相比，土壤胶体在石英砂柱内迁移较快，这可能是由于土壤胶体与石英砂之间相互作用较弱所致。土壤胶体与U(Ⅵ)共存体系中，U(Ⅵ)的迁移速率明显增大，而土壤胶体迁移速率无显著变化，表明共存体系中U(Ⅵ)的迁移行为主要受土壤胶体所控制。静态吸附实验表明，在石英砂-U(Ⅵ)二元体系中，pH≈6.0时石英砂对U(Ⅵ)的吸附率最大，而在胶体-石英砂-U(Ⅵ)三元体系中，U(Ⅵ)主要在土壤胶体表面发生吸附。本研究所用土壤中胶体的质量分数仅约占0.04%，但可吸附20%U(Ⅵ)（初始质量浓度为5.0 mg/L）；由此可见，土壤胶体可与U(Ⅵ)发生强的相互作用，进而对U(Ⅵ)在真实环境体系中的吸附、迁移和扩散等行为产生至关重要的影响。     

二乙基三胺五乙酸浸取-电感耦合等离子体质谱法测定石灰性土壤中有效态铜锌铁锰

采用二乙基三胺五乙酸(DTPA)浸提石灰性土壤样品中有效态Cu、Zn、Fe、Mn后,样品溶液基体盐分较大,此时若直接采用电感耦合等离子体质谱法(ICP-MS)进行测定,极易使仪器的采样锥和截取锥发生堵塞,雾室和炬管积盐,进而影响测定准确性。据此,实验用DTPA浸提样品后,采用对样品溶液稀释10~30倍和在标准溶液系列中加入DTPA溶液进行基体匹配的方法以消除基体干扰,利用氦碰撞模式进行测定以消除多原子离子⁴⁰Ar¹⁶O对⁵⁶Fe的质谱干扰,最终实现了ICP-MS对石灰性土壤中有效态Cu、Zn、Fe、Mn的测定。对氦气流量进行了优化,并确定氦气流量为4.5mL/min。在优化的实验条件下,Cu、Zn的质量浓度为5~200ng/mL、Fe的质量浓度为100~3000ng/mL、Mn的质量浓度为30~1000ng/mL时,各元素质量浓度分别与其计数值呈线性关系,相关系数均不小于0.9998。方法检出限为0.003~0.01mg/kg。按照实验方法测定土壤有效态成分分析标准物质中的有效态Cu、Zn、Fe、Mn,测定值与认定值一致,相对标准偏差(RSD)为1.3%~3.1%。采用实验方法和标准方法HJ 804—2016(电感耦合等离子体原子发射光谱法)进行方法对照试验,二者测定值基本一致。     

含水率对砂岩动态拉伸强度的影响

工程中的岩石具有不同的含水性，研究不同含水率岩石动态力学性质的变化规律，对岩石工程的设计和建设具有很强的指导意义。为研究不同含水率对砂岩动态拉伸强度的影响，利用霍普金森压杆（SHPB）试验装置对不同含水率试样进行了一系列动态巴西劈裂试验，研究了不同含水率砂岩在不同加载率条件下的动态拉伸强度变化规律。试验结果表明：岩石的动态拉伸强度随着加载率的增加而增加，其率相关性与含水率有关，饱和试样的率相关性较强，而干燥岩石的动态强度对加载率的变化不敏感。当加载率较低时，岩石的拉伸强度随着含水率的增加而降低；当加载率较高时，由于水的Stefan效应，水对岩石裂纹产生抗力，阻碍其扩展，导致岩石强度增加，饱和试样的动态拉伸强度出现高于非饱和试样强度的现象。     

基于Kӧtter方程的盾构掘进面上被切削土体受力研究

为了计算不同土体性质与不同掘进参数下盾构刮刀与土体之间的作用力以及由此带来的切削扭矩,引入了修正后的Kӧtter方程作为补充方程,求解出开挖面上土体在被动切削至破坏时滑动面上的应力分布,建立了被切削土体受力模型,求解出刮刀刃面与土体之间的正压力p、摩擦力Q与侧向土体间抗剪阻力U,进而推导出刀盘切削扭矩T的计算公式。分析得到特定刀盘上刮刀的p,Q,U值随土体c,φ值增大而增大,通过适当提高刮刀刃面粗糙度来增大摩擦可使土体更易被切至破坏;p,Q,U值随刀盘转速ω增大而减小,p,Q随支护荷载p线性增大且p对于被切削土体受力的影响在砂性土中较大,最终给出特定刀盘掘进至部分种类土体中的切削扭矩值作为工程参考。     

强夯的物质点法模拟及其能量转化规律分析

提出大应力范围内的密度相关土体本构模型,适用于分析强夯等作用下的土体变形问题。对刚柔接触算法进行了修正,用物质点法结合提出的本构模拟了强夯过程。与其他数值模拟将荷载假设为三角形应力波作为输入荷载不同,通过输入夯锤与土体的碰撞速度实现加载。模拟结果与承德机场4标段某处试验数据进行了对照,吻合较好。提出强夯过程中的能量转化率的概念,对能量转化的规律进行了研究,为研究强夯问题提供了新视角。模拟分析表明,能量转化率的提高不总意味着每击夯沉量的提高,因为能量在较大范围的扩散可能导致高能量转化率下的低夯沉量;剪切变形过程中吸收较多的塑性应变能,可能会使体积压缩变形吸收的塑性应变能向局部集中。通过数值模拟还发现,重锤低落时的能量转化率高于轻锤高落,一般可产生更大的夯沉量。