Preparation of scrap tire rubber fiber–silica fume mixtures for modification of clayey soils

This experimental work was performed to investigate the influence of silica fume–scrap tire rubber fiber mixture inclusion on the geotechnical properties of clayey soils. The natural and modified clayey soil samples were subjected to the unconfined compression, the shear box, the odometer and the falling-head permeability tests after compaction at optimum moisture content. The results of experimental research indicated that silica fume, fiber and silica fume–fiber mixture modification enhanced both the unconfined compression strength and strength parameters. Although, the fiber modification increased in the hydraulic conductivity, it decreased in the swelling pressure. It was observed also that the silica fume and silica fume–fiber modification decreased both the hydraulic conductivity and swelling pressure. Consequently, it is concluded that the silica fume–fiber mixture materials can be successfully used for the modifications of clayey soils in the geotechnical applications.     

Influence of silica fume on the desiccation cracks of compacted clayey soils

Clayey soils containing smectites are widely used for construction of liner and cover systems to reduce the hydraulic conductivity in geotechnical applications because of their low permeability and high cation exchange capacity. However, the compacted clayey soils crack on drying because of their high swelling potential, and their hydraulic conductivities increase. To solve this problem, it is essential to stabilize the clayey soils using additive materials. The aim of this study is to examine the suitability of silica fume as a stabilization material to reduce the development of desiccation cracks in compacted clayey liner and cover systems. Natural clayey soil and clayey soil–silica fume mixtures were compacted at the optimum moisture content and subjected to laboratory tests. The results show that silica fume decreases the development of desiccation cracks on the surface of compacted samples. We concluded that silica fume waste material can be successfully used to reduce the development of desiccation cracks in compacted clayey liner and cover systems.     

Electrokinetic remediation of lead‐, zinc‐ and cadmium‐contaminated soil

Electrokinetic remediation of lead‐, zinc‐ and cadmium‐contaminated sand and clayey soils has been investigated under laboratory‐scale conditions. Soil extracts of heavy metals (by 1 M HCl solution) were analysed by optical emission spectrometry. The efficiency of electrochemical remediation was partially dependent on the pH of the soil media. With pH increase, the migration of heavy metal ions toward the cathode was limited. When acetic acid was added to the sandy soil, almost complete remediation was achieved. A clay layer inserted in the cathode area did enhance the remediation rate. The most effective clean‐up was achieved for zinc and cadmium, with less effective clean‐up being achieved for lead. The effectiveness of the electrokinetic remediation of heavy metal‐contaminated clayey soil was low. The appropriate acidity was not achieved using acetic acid because of the high buffering capacity of clay, and metal ion migration was impeded by its sorption onto some clay components. The conclusion was made that clays could be used as immobilizing media for heavy metal ions by electrokinetic remediation of various soils. © 2001 Society of Chemical Industry     

Fly-ash: An exploitable resource for management of Australian agricultural soils

Agricultural soils in Australia have inherent limitations of structural and nutritional nature that pose major constraints to crop productivity. These soils are still productive due to intensive management that involves routine treatments with lime and gypsum at significant costs both to the farmer and the environment. Production costs associated with these inputs average about 30% of the total cost of soil treatment. Furthermore, reserves of gypsum are under pressure. There is therefore an opportunity for the more than 13 million tonnes of coal combustion products (CCPs) produced annually by coal-fired power stations to be utilised in the management of agricultural soils. At present, about 70% of the ash is emplaced within landfills. In this paper we briefly describe the main constraints of major agricultural soils that could be ameliorated with fly-ash. We used a model to estimate that application of fine (<20 μm) fly-ash to the top 0.15 m coarse textured (sandy) soil would reduce hydraulic conductivity by 25% and so improve water-holding capacity. The same treatment of fine textured clayey soil with coarse (>20 μm) fly-ash would increase conductivity by up to 20%. We cite examples of studies that have shown beneficial use of coal-ash for crop production, including our ongoing glasshouse study in which fly-ash was found to increase early growth vigour and seed yield by 20% for canola (Brassica napus). There are several issues, including costs and regulation, and knowledge-gaps that need to be addressed before adoption of CCP for routine soil management.     

不同方法测定水泥土渗透系数的研究

为研究适合测定水泥土渗透系数的试验方法,结合工程实际,对防渗墙进行现场钻孔注水试验,对钻芯取样的水泥土试样进行室内变水头渗透试验和三轴渗透试验,对比室内试验结果和现场试验结果,探讨适合检测水泥土芯样的室内试验方法,分析三轴渗透试验中孔隙水压和围压对水泥土渗透性的影响。对重新配制的水泥土试样进行室内变水头渗透试验、三轴渗透试验及水泥土渗透试验,研究不同方法测定水泥土渗透系数的差异。试验结果表明:三轴渗透试验比室内变水头渗透试验更适合测定水泥土芯样渗透系数;三轴渗透试验中,围压为0时,水泥土芯样渗透系数会随着孔隙水压的增加而增加,围压改变时,会随着围压的增加而减小;三种室内渗透试验方法测定水泥土试样的渗透系数基本相接近,都可用于测定水泥土试样渗透系数。     

Influence of boundary conditions on transient excess pore pressure during electrokinetic applications in soils

Application of electric currents through saturated silt and clay-rich soils induces electrochemical effects that influence the mechanical and hydraulic behaviour of soft soils. The transient effects of electro- and geo-chemical changes on pore pressure evolution in soil are poorly understood. A major issue, the transient development of non-linear geo- and physico-chemical conditions between the electrodes, is evaluated in this study. An experimental investigation was conducted to provide an understanding of the mechanisms that affect pore pressure or suction development along the sample and consequent transient and non-linear changes. A natural silty soil was used because it accounts for the complex physical and chemical interactions that originate during treatment in the field. Tests were conducted with free drainage at the boundaries and under constant current intensity. The experimental investigation results highlighted the importance of the boundary chemical conditions on the development and transient changes in excess pore pressure along the sample. In particular, the generation of high potential gradients in the first few millimetres of the soil sample dominates the overall pore pressure distribution and behaviour. A relationship between the maximum pore pressure developed and the applied current density is evaluated.     

Electrokinetic treatment for clayed and sandy soils

Electrokinetic treatment has proven to be an attractive alternative to clean polluted soils. This friendly environmental procedure can be approached by a physicochemical model dealing with the oriented displacement of pollutants by means of the fluid and/or charge flow through a porous media induced by an electric field. Concerning the porous media, soil texture is the main issue to consider, since it is related with physicochemical properties that may define the electrokinetic phenomena. In this paper, two different soil textures were tested under the same experimental conditions. Physicochemical characterization of clayed and sandy unpolluted soils, later mixed with PbCO₃, were done. Zeta potential measurements were performed to approach the soil particles interphase with three aqueous solutions. Clayed and sandy soil, mixed with cerusite, were treated by electrokinetics during 24 h. Results for sandy soil contaminated with Pb, using ammonium acetate and acetic acid as anolyte and catholyte respectively, reported Pb mobility due to a fluid flow from anode to cathode; in accordance with zeta potential indicating more negative values for ammonium acetate solution, compared with EDTA and acetic acid. For the clayed soil, lead mobility was detected, even if no electroosmotic flow appeared. Finally, the same experimental conditions were applied to a real soil containing mining wastes, in this case lead mobility was due to electroosmotic and electromigration flow.     

In Situ Electrokinetic Removal of Salts from Greenhouse Soil Using Iron Electrode

An electrokinetic (EK) field study was performed on a pilot scale (2.2 × 3.3 × 0.3 m³, W × L × D) in a greenhouse by using Fe electrodes and bentonite backfill. When a constant voltage gradient was applied, the current intensity was affected by electrode position, and the soil temperature increased with the current intensity. After the EK treatment, the soil pH was little changed and the cations were hardly removed because of the ion exchange in the bentonite. However, the anions were mostly removed by electromigration, resulting in the reduction of the soil electrical conductivity. The field study demonstrated that in situ EK process is feasible for the remediation of greenhouse soils. In addition, the improvement of EK system and the role of bentonite backfill were discussed.     

Enhanced electrokinetic remediation of cadmium-contaminated natural clay using organophosphonates in comparison with EDTA

Soil contamination by metals is a worldwide environmental problem. Electrokinetic extraction is a promising technology for in-situ remediation of contaminated soils of low hydraulic permeability. However, the extraction of metals is usually hindered by the high buffer capacity of natural soils. Organophosphonates are strong metal chelates as ethylenediaminetetraacetic acid(EDTA) which has been widely studied in the enhancement of electrokinetic remediation. In this study, batch desorption experiments and bench-scale electrokinetic extraction experiments were carried out to study the effect of two organophosphonates, i.e.,(nitrilotrimethylene)triphosphonate(NTMP) (ethylenedinitrilo)-tetramethylenephosphonate(EDTMP), on the extraction of cadmium from a natural clay in comparison with EDTA. Results of the batch desorption experiments showed that more than 75% of the sorbed cadmium could be dissolved into solution using 0.1 mol·L~(-1) organophosphonates or EDTA in the wide p H range of 1–11. Results of the electrokinetic extraction experiments showed that the cadmium spiked in the specimen migrated towards the anode with the enhancement of NTMP,EDTMP, and EDTA under a constant voltage gradient of approximately 1.0 V·cm-1. Although cadmium mobilization enhanced by EDTA was more efficient than that by the organophosphonates, accumulation of cadmium was observed in the vicinity of the anode. The average removal efficiencies of cadmium from the soil after approximately 5 days of electrokinetic extraction enhanced by 0.1 mol·L-1 NTMP(22.8%) and EDTMP(22.4%) were higher than that by 0.1 mol·L~(-1) EDTA(15.1%).     

Pulse-enhanced electrokinetic remediation of fluorine-contaminated soil

The presence of abundant fluorides in soil can pose potential threats to environment and human health. We investigated the effects of pulsed electric field on electrokinetic remediation of fluorine-contaminated soil by varying the pulse interval. Although the remediation time was increased, experimental results indicated pulse-enhanced electrokinetic remediation could improve the removal efficiency of fluorine better than the conventional electrokinetic remediation in the same intensity of electric field. The fluorine removal efficiency of the former (30 min, pulse interval) was 80.93% and that of normal electrokinetic remediation was 72.40%, because pulsed electric field could reduce the concentration polarization and increase the electrical current, electroosmotic flow and the electrical voltage part in soil cell. Therefore, in the later phase of electrokinetic remediation, when electrical current and the fluorine removal efficiency decreased obviously, at this time the pulse-enhanced method would be a considerable choice to eliminate fluorine in contaminated soils.     

火灾作用下钢筋混凝土基础隔震结构连续倒塌分析

为了得到火灾发生后基础隔震结构倒塌性能, 先进行了铅芯橡胶隔震支座在高温下力学性能的研究。通过ABAQUS有限元软件，建立了铅芯橡胶隔震支座和基础隔震框架的有限元模型并进行热力耦合分析。分析了火灾高温下橡胶隔震支座竖向刚度变化规律以及基础隔震框架结构的倒塌机制、应力状态、变形规律和塑性铰分布规律。结果表明：铅芯橡胶隔震支座的竖向刚度随受火时间的增长而逐渐降低，受火75 min时完全失去承载力；基础隔震框架不同位置支座受火时，框架呈现不同的应力、变形状态；边支座和内部双支座受火时，框架发生连续倒塌。     

Integrated electrokinetic-soil flushing to remove mixed organic and metal contaminants

The integrated use of hydraulic flushing and electrokinetic treatment was investigated for the remediation of silty sand contaminated by both PAHs and heavy metals. The soil was collected from a polluted former manufactured gas plant (MGP). Four bench-scale experiments were conducted to analyze the ability of the combined hydraulic flushing and the electrokinetic treatment for the simultaneous removal of PAHs and heavy metals. Sequential flushing with ethylenediaminetetraacetic acid (EDTA) or Igepal CA-720 were tested with or without the simultaneous application of a low intensity direct electric field (1 VDC cm⁻¹). The best results were obtained with 0.2 M EDTA flushing in two stages (without and with voltage gradient, 1 VDC cm⁻¹), followed by 5% Igepal flushing in two stages (without and with 1 VDC cm⁻¹). Heavy metals were removed mainly during the EDTA flushing, with removal efficiencies of about 60% for Zn, 80% for Pb, and 30% for Cu. During Igepal flushing, no heavy metals were removed, but PAHs were removed, including 40% phenanthrene, 30% pyrene, and 20% benzo[a]pyrene. Overall, this study showed that a carefully designed sequential hydraulic flushing scheme with selected chelant and surfactant is needed for the removal of both heavy metals and PAHs from MGP silty sands. Combining electrokinetics with hydraulic flushing may not necessarily improve contaminant removal from such soils.     

Hygroscopic-aging behavior of pure and NaCl-filled polyurethane rubber

The aging phenomenon of highly filled rubber in humid environment was investigated. HTPBD was reacted with MDI and mixed with salt at the same time. The mixture was then hot-pressed for 24 h at 90°C to prepare the sample. The changes in mechanical properties and glass transition temperature of the sample were followed when they were subjected to different humidity at 30°C for 7 days. Furthermore, the effects of humidity on chemical structures were studied with IR. The results showed that unfilled rubber suffered no changes in mechanical properties after 7 days in environment of high humidity (RH 97). However, for NaCl-Filled rubber, its strength decreased because of a loss of stiffness of salt after salt deliquesced. The glass transition temperature of unfilled rubber seems not to be affected by various humid conditions, but the T_g of filled rubber decreased slightly. From SEM pictures, we observed that interior holes were left after salt deliquesced. This was the main cause for the reduction in mechanical properties of filled rubber.     

Preliminary tests of an electrokinetic barrier to prevent heavy metal pollution of soils

Sardinia has to deal with significant environmental problems related to heavy-metal contamination, mainly located at its abandoned mining districts. In particular, acid mine drainage management and groundwater pollution are typical problems associated with mining activities which constitute a serious threat to human health. To prevent contaminant spread over the adjacent environment, it is of great interest to consider using an electric field as a containment fence to counteract pollutant transport. In this application, contaminant transport due to a hydraulic gradient driving force is prevented by the combined effect of electro-osmosis and electro-migration. Although there are other alternative containment technologies, the electrokinetic fence offers many advantages, as it is easy to operate, there is a minimal exposure to the operating personnel and it is likely to be effective for a wide range of contaminants. In this work, both one-dimensional (1D) and two-dimensional (2D) tests have been carried out. In the 1D tests, the efficiency of an electrokinetic barrier to prevent cadmium from polluting an uncontaminated sample was investigated; soil pH, metal concentration and current intensity have been monitored; results indicate that the barrier can prevent or significantly reduce heavy-metal contamination from spreading against a hydraulic gradient of 7. In 2D tests, two rows of electrodes inserted in a horizontally flat soil tank were used to generate an electric field. It was found that an electric field of 125 V m⁻¹ was sufficient to prevent significant copper incursion from a contaminant flow under a hydraulic gradient of 1.3.     

冬小麦生育期不同保水措施土壤水分变化研究

研究了不同保水措施及灌水对小麦田表层土壤保水及入渗性能的影响。结果表明,总的趋势是随着保水剂用量的增加,保水性能增强。在越冬期内,秸秆覆盖下的土壤表层水分略高于保水剂处理;从返青期到孕穗期,灌水和不灌水处理的土壤表层水分消耗差异明显,灌水处理的表层土壤含水量比不灌水处理下降的多;在孕穗后期,灌水处理表层土壤含水量明显高于不灌水处理,且随保水剂用量增加而增加,秸秆覆盖处理稍低于保水剂处理;收获后,处理间差异不显著。在土壤导水方面,耕作和保水措施都提高了土壤渗透性能,传统耕作和灌水处理均降低了土壤饱和导水率。灌水条件下,保水剂用量45kg／hm^2时有利于提高土壤饱和导水率。     

The role of composition and fabric of soils in selected geotechnical engineering case histories

Geotechnical engineering typically involves the prediction of performance of foundations or earth structures. The basic tools of the geotechnical engineer are the engineering properties of the soil (strength, deformability, compressibility and permeability) and theoretical predictive models. However, problems or geotechnical features which require more detailed information beyond the fundamental engineering properties of the soil are often encountered. Deficiencies in the traditional engineering approach are not usually related to inadequate theory but rather to an inadequate understanding of the soil properties. Examples include collapsing soils, highly plastic overconsolidated clays, anisotropic soils, soft clays and locked sands. Knowledge of the clay mineralogy and fabric can help in developing a better understanding of soil behaviour.Three case histories are examined wherein unusual soil performance or engineering properties were encountered. The clay mineralogy and fabric are examined for each case. The first case involves an embankment failure on glacial Lake Edmonton clay. The clay is highly plastic and shows a pronounced secondary structure that controls mass strength. The second case is a clay from the Beaufort Sea. It has the unusual characteristic of the horizontal stress being up to twice the vertical stress. The third case deals with a clayey silt with which a serious foundation problem was experienced at the University of Calgary library during construction. In addition, two other unusual soils are examined. One is from a stratum of soil located under a large retaining wall in Banff National Park. The second is collapsing soil from Kamloops, B.C.     

Restoration of saline greenhouse soil and its effect on crop’s growth through in situ field-scale electrokinetic technology

An in situ electrokinetic (EK) system was designed and applied to highly saline greenhouse soil with a view to investigating the effects of the EK process on growing crops. In situ EK tests in field scale were conducted on the salt accumulated lands in the greenhouse where cabbages and lettuces were being cultivated. A voltage gradient of 0.25–0.6 V cm^?1 was applied for 50 days in the cultivated lands. The changes in the process, viz. current, voltage, and soil temperatures, were monitored. After the EK process, the initial electrical conductivity (EC, 6.0 dS m^?1) of the soil was reduced to about 1.7 dS m^?1 homogeneously below the recommended value (2.5 dS m^?1). The growth rate of cabbages and lettuces under EK treatment was about twice higher than those in the untreated area. The present study revealed that the EK process encourages the growth of the crops considerably and also removes the salts in the soil efficiently during the growth of the crops.     

Influence of previous annealing on first stage of degradation of blends of low‐density polyethylene and Mater‐Bi AF05H aged in soil: Comparative thermal analysis study

Samples of low‐density polyethylene (LDPE) filled with a commercial biodegradable material (Mater‐Bi AF05H) were subjected to an accelerated soil burial test in a culture oven. In addition, another series of these blends was subjected to thermal treatment and afterward buried in soil under the same conditions. Comparative studies of the changes in the thermal stability and the structural and morphological properties of the samples were carried out by means of differential scanning calorimetry, dynamic mechanical thermal analysis, and thermogravimetric analysis. The morphological properties under study were the melting temperature, the crystalline content, and the lamellar thickness distribution. The α_I relaxation zone of the mechanical spectra was characterized in terms of tan δ, whereas the α_II and relaxation zones were characterized in terms of E″ according to the Fuoss–Kirkwood equation and with the help of a deconvolution method. Finally, the kinetics of each thermodegradation process was studied using the Broido integral method. The Mater‐Bi hindered the uniform growth of crystallites in PE and facilitate molecular motions, but the thermal treatment seemed to rearrange the crystallites in the crystalline phase of PE and promote segregation of the crystallite sizes. These molecular reorganizations affected the degradation process so that the degradation of the polymeric matrix seemed to be obstructed by the annealing during the first 120 days of aging in soil and only the Mater‐Bi degradation could be observed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3359–3373, 2003     

Evaluation of lead removal from sandy soils using different electrolytes in electrokinetic experiments: prospective for remediation of a real site contaminated with mining wastes

The mixture of mining wastes with native soil has similarities with a low permeable porous structure in respect of electrical conductivity and adsorption capacity; therefore, electrokinetics appears as a suitable remediation treatment for sites containing potential toxic elements as Pb, Cd and As. In particular, this paper focuses on the evaluation of the main electrokinetic phenomena that removes Pb(II) from the model sandy soil (98.5% sand and 1.5% clay). For this purpose a study of five different electrolytes, used as moisturizing solution, as well as electrolytes, was done. Results from zeta potential measurements and electrokinetic experiments indicate that ammonium acetate and acetic acid were the best electrolytic solution that ensures the greater Pb removal from sandy soil contaminated with PbCO₃.     

The long-term effects of manures and fertilisers on soil productivity and quality: a review

The results from 14 field trials comparing the long-term (20 to 120 years) effects of fertilisers and manures (farmyard manure, slurry, and green manure) on crop production and soil properties are reviewed. In total there were 24 paired comparisons of the effects of manure and fertiliser. Some of the trials also contained a control (no nutrient inputs) treatment. The input of nutrients as either fertilisers or manures had very large effects (150–1000%) on soil productivity as measured by crop yields. Manured soils had higher contents of organic matter and numbers of microfauna than fertilised soils, and were more enriched in P, K, Ca and Mg in topsoils and nitrate N, Ca and Mg in subsoils. Manured soils also had lower bulk density and higher porosity, hydraulic conductivity and aggregate stability, relative to fertilised soils. However, there was no significant difference (P < 0.05) between fertilisers and manures in their long-term effects on crop production. In the context of this set of international trials, the recent evidence from the Rothamsted classical long-term trials appears to be exceptional, due to the larger inputs of manures and larger accumulation of soil OM in these trials. It is suggested therefore that manures may only have a benefit on soil productivity, over and above their nutrient content, when large inputs are applied over many years. The evidence from these trials also shows that, because the ratio of nutrients in manures is different from the ratio of nutrients removed by common crops, excessive accumulation of some nutrients, and particularly P and N, can arise from the long-term use of manures, relative to the use of fertilisers. Under these conditions greater runoff of P, and leaching of N may result, and for soils with low P retention and/or in situations where organic P is leached, greater P leaching losses may occur. The use of manures, relative to fertilisers, may also contribute to poor water quality by increasing its chemical oxygen demand. It is concluded therefore that it cannot generally be assumed that the long-term use of manures will enhance soil quality – defined in terms of productivity and potential to adversely affect water quality – in the long term, relative to applying the same amounts of nutrients as fertiliser.