Dry Weight Of Soil Research Articles

Undrained cyclic loading response of lignosulfonate treated high plastic clay

In this study, a non-traditional and environment friendly chemical stabilizer, lignosulfonate has been used to stabilize high plastic clay and its effectiveness has been investigated through a series of static and cyclic loading tests. Unconfined compression tests were conducted for various percentages of lignosulphonate contents (0.5, 0.75, 1.5, 2.0, 2.5 and 3.0%) by weight of dry soil at curing periods of 5, 10 and 21 days. Shear strength and deformation characteristics of stabilized specimens were examined, corresponding to optimum content of lignosulfonate at which unconfined compressive strength was maximum, for different confining pressures and cyclic stress levels under unconsolidated undrained conditions. Test results indicated a significant increase in unconfined compressive strength and shear strength under static loading; whereas, reduction in axial strains and rate of permanent strain development, and increased resilient modulus under cyclic loading. In addition, SEM analysis has also been conducted to understand the microstructural changes occurring in the soil due to addition of lignosulfonate.

Strengthening Soft Clayey Subgrade Soil Layer Using Cement Kiln Dust and Palm Kernel Ash Materials

The product materials which are generated from industrial manufacturing are used to enhance the engineering and chemical properties of soil. There are three phases of soil improvement are improvement without the addition of any other material, adding certain materials, and providing reinforcement. This study used materials product from industrial and waste materials as additives to improve the physical properties and strength of clayey soil subgrade under foundation and flexible pavement structure. This study has been investigated the effect of isolated and combined Cement Kiln Dust (CKD) and Palm Kernel Ash (PKA) materials on strength of clayey soil as tested by California Bearing Ratio (CBR) test. Various percentages of CKD and PKA materials were added to clayey soil samples to determine the optimum percent of CKD and PKA. The results showed that CKD and PKA have improved soil strength at the optimum compound percent of CKD content was 8% and PKA was 2% by weight of dry soil.

Improvement of Soft Clay Soil Using Different Types of Additives

This study deals with the evaluation of the stabilization of several samples of soft soil with some chemical and physical additives. The intention is to amend the weak properties of these soils summarized in low bearing capacity and high settlement. The used stabilizers are quicklime, class F fly ash activated by cement, rock powder, crushed waste concrete, and tire crumb rubber. The paper investigated the effects of these stabilizers by unconfined compression test that considers very effective geotechnical test for measuring the ability of soils to bear structures constructed on them especially when used additives. This test was carried out on three samples of soils. They were classified by (UCSC) as (CL) soft soils. They were also classified by (AASHTO) as (A-7-6), (A-6), and (A-6) are rated as fair to poor subgrades in (AASHTO). The results of (UCS) test for each of the five additives used were compared according to the responding of each soil samples used. The (UCS) test was conducted in this study on sixty samples of soils before and after treatment and under the basics of the Proctor compaction test at optimum moisture content and maximum dry density. The results showed that the rock powder was the most suitable stabilizer that gave best results of improvement reached to 900% at 25% percent by dry weight of soil, crushed waste concrete came after it that gave treatment 683% at 15%, class F fly ash activated by cement followed the two formers which increased strength 533% at 15%, quicklime after that in an amendment 517% at 9% and finally tire crumb rubber that stabilized the soil 500% at 4%. In the literature, these materials founded to be very efficient in the stabilization of soils in their physical and chemical properties like increasing bearing capacity and reducing settlement of soil.

Effect of optimum utilization of silica fume and eggshell ash to the engineering properties of expansive soil

The utilization of substance stabilizer in soil improvement can diminish the obstructive ecological effect in the development business, and respond as the soil stabilizers to the kaolin clay soils. In any case, the improvement of kaolin clay stays a test because of the significant expense and non-eco-accommodating materials like concrete and lime. This examination exhibits the capacity of SF in the mix with ESA in stabilizing the delicate kaolin clay soils, by means of particle size distribution (PSD), specific gravity, Atterberg limits, compaction parameters and undrained shear strength (USS) parameters. Its impact on the undrained shear strength upgrade was concentrated through the concrete substitution material in kaolin clay soil at the replacement degree of 2%, 4% and 6% (by dry weight of kaolin clay soil) of SF and ESA replacements of 3%, 6% and 9% (by dry weight of kaolin clay and SF content). The consideration of SF with ESA shows a lower specific gravity (4.9% decrease), lower plasticity index (PI) (48.4% decrease), diminished maximum dry density (MDD) (5.5% decrease), expanded in optimum moisture content (OMC) (8.7% increase), and higher USS (68.8%) when contrasted with the untreated kaolin clay soils and those treated with SF. The blends of SF and ESA as soil adjustment specialists effectively upgrade the undrained shear strength of the kaolin clay soils up to 68.8% strength improvement with the best percentage of 6% SF and 6% ESA for optimum enhancement of the expansive soil, which minimizing the expenses and as an eco-accommodating materials in soil improvement.

Drained behaviour of artificially cemented dune aeolian sand

ABSTRACT Mixing cement and soil is a traditional technique used to improve their mechanical properties. Other studies proposed a rational dosage methodology for soil-cement mixtures. This method is based on the void-cement ratio and aimed at obtaining a particular strength level. The present study evaluated the validity of the void-cement ratio (η/Civ) and analysed the stress – strain – strength behaviour of aeolian dune sand from Natal, Brazil, mixed with cement. Isotropically consolidated drained triaxial compression tests (CID-C) were conducted with moulded samples containing 0.0, 2.5, 5.0 and 7.5% cement by weight of dry soil. Void ratios corresponded to three conditions of relative density: loose, medium and dense, with confining stresses of 50, 100, 200 and 300 kPa. The effect of void ratio, cement content and void-cement ratio on the stress-strain-strength behaviour of the mixtures was determined. The results showed that the void-cement ratio is an appropriate parameter to assess the effective strength of the cement-sand mixture studied.

Pathogen and heavy metal contamination in urban agroecosystems of northern Ghana: Influence of biochar application and wastewater irrigation.

The benefit of biochar as a soil fertility enhancer is well known and has been broadly investigated. Equally, many tropical and subtropical countries use wastewater for irrigation in urban agriculture. To assess the related health risks, we determined pathogen and heavy metal fate associated with biochar application and wastewater irrigation in the urban agriculture of northern Ghana. Rice (OryzaL.) husk biochar (20 t ha-1 ), N-P-K 15-15-15 fertilizer (212.5kg ha-1 ), and their combinations were evaluated in a field-based experiment. Untreated wastewater and tap water served as irrigation water. Red amaranth (Amaranthus cruentus L.) was used as a test crop and was grown in wet (WS) and dry (DS) cropping seasons. Irrigation water, soil, and vegetables were analyzed for heavy metals, Escherichia coli, fecal coliform, helminth eggs, and Salmonella spp. Unlike the pathogens, analyzed heavy metals from irrigation water and soil were below the FAO/WHO permissible standard for agricultural activities. Wastewater irrigation caused E. coli concentrations ranging from 0.5 to 0.6 (WS) and from 0.7 to 0.8 (DS) log10 colony forming units per gram fresh weight (CFU gFW -1 ) on vegetables and from 1.7 to 2.1 (WS) and from 0.6 to 1.0 (DS) log10 CFU per gram dry weight (gDW -1 ) in soil. Average log10 CFU gFW -1 rates of 6.19 and 3.44 fecal coliform were found on vegetables, whereas in soil, 4.26 and 4.58 log10 CFU gDW -1 were observed in WS and DS, respectively. Helminth egg populations were high in wastewater and were transferred to the crops and soil. Biochar did not affect bacteria contamination. Pathogen contamination on vegetables and in soil were directly linked to the irrigation water, with minimal or no difference observed from biochar application.

Estimation of Optimum Moisture Content and Maximum Dry Unit Weight of Fine-Grained Soils using Numerical Methods

Soil compaction is one of the basic engineering techniques, which is carried out to guarantee the stability of soils dependent on specified strength. Nonetheless, in large-scale construction projects, the estimation of compaction features required tremendous effort and time that can be saved utilizing empirical relationships at the initial phases. It becomes critical to develop models to predict the compaction features, namely the maximum dry unit weight (γdmax) and optimum water content (WOP). This article attempts to develop models to predict the γdmax and WOP of fine-grained clay soils. Geotechnical tests such as grain size distribution, Atterberg limits, specific gravity, and proctor compaction tests are performed to assess soil samples' physical and hyro-mechanical characteristics. Multivariate analysis is conducted using MINITAB 18 software to develop the predictive models. The validation process of developed models includes the determination coefficient, probability value (p-value), comparison of the predicted values with experimental values, comparison of the models proposed in this study with other existing models found in the recent literature, and employing a different soil data set. The predicted values obtained from the models proposed in this research project are more accurate than other models developed recently. The proposed models estimate the compaction features of fine-grained clay soils with acceptable precision.
 HIGHLIGHTS
 
 Soil compaction is one of the basic engineering techniques perform to guarantee the stability of soils dependent on specified strength
 In large-scale construction projects, the estimation of compaction parameters required tremendous effort and time that can be saved utilizing empirical relationships at the initial phases
 This study has developed semi-empirical models to predict the compaction parameters (maximum dry unit weight and optimum water content) of fine-grained soils
 
 GRAPHICAL ABSTRACT

An Experimental Investigation on Black Cotton Soil using Terrazyme

The application of biodegradable substances for the improvement of weak soil has given better results in the field of geotechnical engineering. These substances are fermented and extracted from vegetation. It reduced the void ratio, thickness of absorbed water and maximize the compaction. Terrazyme contains natural protein. It is non-toxic and eco-friendly. It is soluble in water. The black cotton soil is highly plastic with swelling potential. Reduction in moisture causes shrinking, leads to differential settlement of the foundation. This will results in damage to the structure. This paper presents experimental work on black cotton soil reinforced with Terrazyme. Various proportions of Terrazyme were mixed with black cotton soil to evaluate the engineering properties of soil. The change in index properties and strength parameters were assessed by experiments on treated and untreated soil. Atterberg limits, free swell index, compaction test, triaxial tests were performed. Experimental results show a reduction in liquid limit, plasticity index, free swell index, optimum moisture content, and compression index. Triaxial tests showed improvement in cohesion and angle of shearing resistance. The optimum dosage of Terrazyme was found 2% by weight of dry soil.

Bioaugmentation with As-transforming bacteria improves arsenic availability and uptake by the hyperaccumulator plant Pteris vittata (L).

Inorganic arsenic (As) is a toxic and carcinogenic pollutant that has long-term impacts on environmental quality and human health. Pteris vittata plants hyperaccumulate As from soils. Soil bacteria are critical for As-uptake by P. vittata. We examined the use of taxonomically diverse soil bacteria to modulate As speciation in soil and their effect on As-uptake by P. vittata. Aqueous media inoculated with Pseudomonas putida MK800041, P. monteilii MK344656, P. plecoglossicida MK345459, Ochrobactrum intermedium MK346993 or Agrobacterium tumefaciens MK346997 resulted in the oxidation of 5–30% As(III) and a 49–79% reduction of As(V). Soil inoculated with P. monteilii increased extractable As(III) and As(V) from 0.5 and 0.09 in controls to 0.9 and 0.39 mg As kg−1 soil dry weight, respectively. Moreover, and P. vittata plants inoculated with P. monteilii, P. plecoglossicida, O. intermedium strains, and A. tumefaciens strains MK344655, MK346994, MK346997, significantly increased As-uptake by 43, 32, 12, 18, 16, and 14%, respectively, compared to controls. The greatest As-accumulation (1.9 ± 0.04 g kg−1 frond Dwt) and bioconcentration factor (16.3 ± 0.35) was achieved in plants inoculated with P. monteilii. Our findings indicate that the tested bacterial strains can increase As-availability in soils, thus enhancing As-accumulation by P. vittata. Novelty statement Pteris vittata, a well-known As-hyperaccumulator, has the remarkable ability to accumulate higher levels of As in their above-ground biomass. The As-tolerant bacteria-plant interactions play a significant role in bioremediation by mediating As-redox and controlling As-availability and uptake by P. vittata. Our studies indicated that most of the tested bacterial strains isolated from As-impacted soil significantly enhanced As-uptake by P. vittata. P. monteilii oxidized 20% of As(III) and reduced 50% of As(V), increased As-extraction from soils, and increased As-uptake by 43% greater compared with control. Therefore, these strains associated with P. vittata can be used in large-scale field applications to remediate As-contaminated soil.

Assessment of swelling and strength characteristics of expansive soil with addition of WRP

ABSTRACT The moisture migration and high-volume changes due to swelling and shrinkage in the expansive soils have posed severe challenges at many project sites. Additionally, rapid industrialisation in last few decades has posed problems of huge amount of undisposed industrial wastes, which not only cause environment degradation but also occupy huge tracts of valuable land. The paper presents the results of an experimental investigation carried out to assess the effect of waste recycled product (WRP), an industrial waste from steel industries; on the engineering properties of expansive soil and to achieve dual objectives of improving the engineering performance of such soils combined with its gainful utilisation. Test results revealed that addition of WRP to expansive soil in appropriate proportion not only reduces its swelling and shrinkage behaviour but also there is a significant improvement in its strength and deformation characteristics. After adding 30% WRP (by dry weight of soil) in expansive soil, the percentage increase in subgrade modulus and unconfined compressive strength was 89.18% and 68.78%, respectively, and it is concluded that there is significant potential for its use in flexible pavement construction on expansive soil subgrade which in turn provides its safe and economical disposal.

Effect of C:N:P stoichiometry on soil nitrous oxide emission and nitrogen retention

AbstractBackgroundIncorporating high organic carbon amendments (HCA) in the soil can promote microbial nitrogen (N) immobilization. HCA incorporation is thought to reduce N loss via nitrate (NO3−); however, it often increases nitrous oxide (N2O) emissions in upland soils.AimsWe aimed to investigate N2O emission and soil N retention in different soils after co‐application of mineral N fertilizer, HCA, and phosphorus (P) fertilizer for alleviating potential microbial P limitation.MethodsWe conducted a 42‐day incubation experiment with nutrient‐rich silty soil (RUS), nutrient‐rich sandy soil (RSS), and nutrient‐poor silty soil (PUS). Soils were amended with wheat straw, leonardite or sawdust, with 50 mg N kg–1 soil dry weight (dw) and additionally with 0, 140, or 250 mg P kg–1 soil dw.ResultsThe addition of 250 mg P kg–1 significantly increased CO2 emission by 88.6% and 19.8% in wheat straw‐amended PUS and RUS, respectively. In the nutrient‐rich soils, HCA co‐applied with P mostly did not reduce N2O emissions. In the sandy soil, sawdust and leonardite with 140 mg P kg–1 significantly reduced the cumulative N2O emissions by 76.3% and 76.8%, respectively. In the silty soils amended with wheat straw, the retention of N in the form of microbial biomass and ammonium in soil was paralleled by significantly lower NO3− concentrations.ConclusionsWe conclude that P co‐application with HCA, such as wheat straw, might improve N retention, even if N2O emissions did not decline. However, we also found that different soils respond very differently to combined HCA, N and P addition, which calls for further research into the underlying mechanisms.

The persistent impacts of polyester microfibers on soil bio-physical properties following thermal treatment

Soilborne microplastics can persist for decades and their consequences are of growing concern. Therefore, it is important to explore the feasible approaches for eliminating microplastic effects on soil properties. Through an incubation experiment, we evaluate the effects of thermal treatment on physical properties, enzymatic activities and microbial communities in polyester-microfibers contaminated soils. The effects of polyester-microfiber levels (0%, 0.1%, 0.3% and 1.0% of soil dry weight) on soil properties were detected under not heated (PMF), heated (mPMF) and added with natural-organic-matters (OM) following heated (mPMF+OM) conditions. Our results showed that 1.0% mPMF soil had lower bulk density and higher mean weight diameter than 0% mPMF soil, akin to PMF soils. Meanwhile, great volumes of < 30 µm pores in 0.3% and 1.0% mPMF soils were observed than that in 0% mPMF soil. Additionally, the dose-effects of melted polyester-microfiber on soil enzymatic activities and bacterial communities were still observed following thermal treatment, even under the OM added condition. Furthermore, our results demonstrated that polyester microfibers influenced soil microbial communities and functioning via altering specific soil physical properties, regardless of thermal treatment or not. Results of this study should be useful to guide further develop viable methods for remediating soils contaminated with microplastics.

Toxicokinetics of hydrophobic organic compounds in oligochaeta: A critical review

Toxicokinetic studies appertain to the fundamental research of soil bioavailability. However, the research outcomes of aspects influencing uptake and elimination of hydrophobic organic compounds have not been summarized so far. In our review, a recapitulation of available toxicokinetic data (i.e. experimental conditions, if the steady state was reached, uptake and elimination rate constants, and bioaccumulation factors) is presented in well-arranged tables. Further, toxicokinetic models are overviewed in the schematic form. In the review, the required information could be quickly found and/or the experimental gaps easily identified. Generally a little is known about the effects of soil properties other than soil organic matter. Limited or no data are available about soil treatment, food supply during laboratory exposure, and metabolization in oligochaeta. The impact of these factors might be important especially for arable soils with typically low organic matter content but high consequences on humans. Besides these circumstances, other uncertainties between published studies have been found. Firstly, the scientific results are provided in heterogenous units: bioaccumulation factors as well as the rate constants are reported in dry or wet weight of soil and earthworms. The steady state is another critical factor because the time to reach the equilibrium is influenced not only by soil and compound characteristics but for example also by aging. Nevertheless, toxicokinetic studies bring irreplaceable information about the real situation in soil and our review help to define missing knowledge and estimate the scientific priorities.

Perbandingan Kepadatan Kering Tanah Lempung Distabilisasi Serbuk Arang Tempurung Kelapa dengan Serbuk Arang Bambu

Clay soil is the basic part of a building construction, but such type of soil has the stability problems, hence it needs to be stabilized to increase its bearing capacity. Some natural materials in Bangka Belitung Province have not been optimally utilized, e.g. coconut shells and bamboo, which can be used as stabilization materials. In this article, we compare the dry density of clay soil mixed with coconut shell charcoal powder to clay soil mixed with bamboo charcoal powder. The percentage of stabilizing material used is 5%, 10% and 15% of the dry soil weight. Soil classification is based on the Unified Soil Classification System (USCS) standard including the low plasticity inorganic clay (CL) group and following the standards of the American Association of State Highway and Transportation Officials Classification (AASHTO) including the A-6 soil group. The compaction test result show that the dry density of the clay soil increases with the addition of stabilization agent using either coconut shell charcoal powder or bamboo charcoal powder. The results were almost the same where the difference was only about 0.001 (gr / cm3) for the stabilizer mixture of 5% and 10% as well as the difference of 0.002% (gr / cm3) for the stabilizer mixture of 15%. The increase in soil dry density indicates that the bearing capacity of clay soil increases with the increase in the percentage of stabilizing material

Evaluation and risk assessment of heavy metals in surface water collected along the Isipingo River, KwaZulu-Natal, South Africa

ABSTRACT In this study, the pollution levels, sources, and ecological risks associated with five selected heavy metals (chromium, copper, iron, lead, and zinc)were evaluated in surface water, soil, and sediment systems along the Isipingo River, KwaZulu-Natal, South Africa. The surface water, soil and sediment samples collected along the river, were preserved, transported, and stored followed the standard procedures. Soil and sediment samples were digested for heavy metal determination using a microwave digestion system. The digested samples were quantitatively analysed using an inductively coupled plasma optical emission spectrometer (ICP-OES). The results demonstrate that majority of the targeted heavy metals were found below the detection limits in surface water except for iron (Fe), which was found within the concentration range of 9.54 to 46.76 µg/L. Lead was found below the detection limit in water, soil, and sediment samples, while other heavy metals were within the range not detected(ND)to 0.222 µg/kg dry weight and 0.212 µg/kg dry weight in soil and sediment respectively. The ecological risk assessment of the studied metals in soil and sediment systems from this riversignified that water from this river had less probable potential adverse effects on both animals and humans as well as benthic organisms.

Comparison of fly ash with Lapindo mud as a land stabilizer for landfill in Pasuruan–Indonesia

The paper discusses the comparison of fly ash with Lapindo mud as a land stabilizer for a landfill in Pasuruan, Indonesia. Land for landfills has a low level of stability due to the condition of garbage that has accumulated and undergoes a process of decay. This land condition is less favorable to support the construction of the building above it if one day the location is used for construction. Therefore, it is necessary to stabilize the soil first. The purpose of this study was to determine the effect of adding a mixture of TPA soil with fly ash and Lapindo mud. The method used by sieve testing and compaction of the specimens for each treatment consisted of a mixture of TPA soil with fly ash and TPA soil with Lapindo mud, while the percentages of fly ash and Lapindo mud to the dry weight of the original soil were respectively 0 %, 10 %, 15 %, and 20 %. The results showed that stabilization of the landfill with fly ash reduced the silt content while stabilization with Lapindo mud increased the levels of silt in the landfill so that fly ash was better than Lapindo mud for stabilization of the landfill. The specific gravity values for both stabilization mixtures increased equally. Based on the results of the standard compaction test for the addition of a mixture of fly ash, the OMC value decreases and the greater the value of dmaxs indicates that fly ash is good for landfill stabilization, while the addition of a mixture of Lapindo mud increases the OMC the smaller the value of dmaxs. For the direct shear test of the two mixed soils, the value of the internal friction angle (Æ) increased. The percentage value of the optimum mixture of mixed soil+fly ash is 14 % with an internal shear angle (Æ) of 38°, while the stabilization of landfill with Lapindo mud obtained the optimum mixture percentage value of 11 % with an internal shear angle (Æ) of 31°

Reinforcing effect of recycled polypropylene fibers on a clayey lateritic soil in different compaction degrees

The present research investigates the reinforcing effect of recycled polypropylene (R-PP) fibers on a compacted clayey lateritic soil in different compaction degrees. R-PP fibers of 12 mm length were mixed with the soil in the contents of 0.1 and 0.25% of soil dry weight. Unconfined compression strength tests (UCS), direct shear tests and indirect tensile strength (ITS) tests were conducted. Fibers addition showed no significate alterations in the optimum compaction parameters. The study evidenced increases in UCS, changing the soil behavior from a brittle failure to a ductile failure, while fiber contribution was most effective for 0.25% R-PP fibers content and 95% compaction degree. The use of fibers improved the shear stress-strain behavior of the composites and soils compacted at different degrees of compaction showed similar shear behavior, which is coherent to the soil water retention curves (SWRC) results. Significant increases in the tensile behavior of soil-mixtures for both fiber contents used were observed, and fibers increase was more significate than increase in soil degree of compaction. The stretching of the fibers and fibers orientation at the sheared interface in direct shear tests and the fiber “bridge” effect in ITS tests could be observed.

Ammonium promoting methane oxidation by stimulating the Type Ia methane-oxidizing bacteria in tidal flat sediments of the Yangtze River estuary

Estuary and coastal environments have essential ecosystem functions in greenhouse gas sinks and removal of nitrogen pollution. Methane-oxidizing bacteria (MOB) and ammonia-oxidizing bacteria (AOB) communities play critical functions in the estuary's tidal flat sediments. Therefore, the effects of ammonium on MOB communities and methane on AOB communities need to be further explained. In this study, microcosm incubations with different contents of ammonium or methane were conducted for a relatively short (24 h) or long (28 days) period with tidal flat sediments from the Yangtze River estuary. Subsequently, the tagged highly degenerate primer PCR and DNA-based stable isotope probing method were employed to demonstrate the effects on MOB and AOB populations. The results indicated that the methane consumption was enhanced with ammonium supplements within 24 h of incubation. Supplement of 2 μmol/g d.w.s (μmol per gram dry weight soil) NH4+ increased the amount of MOB and its proportion to the total bacteria (p < 0.05) for 28 days incubation. The ammonium supplement increased the proportion of Methylomonas and Methylobacter based on the 16S rRNA gene. According to the functional gene analysis, the MOB primarily engaged in methane oxidation include Methylomonas, Methylobacter, Methylomicrobium, and Methylosarcina, which were associated with Type Ia MOB. It suggested that ammonium supplement may promote methane oxidation by stimulating the Type Ia MOB in tidal flat sediments of the Yangtze River estuary. The current research helps understand the effect of ammonium on methane consumption in the estuary and coastal environments.

Effect of Confining Conditions on the Hydraulic Conductivity Behavior of Fiber-Reinforced Lime Blended Semiarid Soil.

The hydraulic properties of expansive soils are affected due to the formation of visible cracks in the dry state. Chemical stabilization coupled with fiber reinforcement is often considered an effective strategy to improve the geotechnical performance of such soils. In this study, hydraulic conductivity tests have been conducted on expansive clay using two different types of fibers (fiber cast (FC) and fiber mesh (FM)) exhibiting different surface morphological properties. The fiber parameters include their dosage (added at 0.2% to 0.6% by dry weight of soil) and length (6 and 12 mm). Commercially available lime is added to ensure proper bonding between clay particles and fiber materials, and its dosage was fixed at 6% (by dry weight of the soil). Saturated hydraulic conductivity tests were conducted relying on a flexible wall permeameter on lime-treated fiber-blended soil specimens cured for 7 and 28 days. The confining pressures were varied from 50 to 400 kPa, and the saturated hydraulic conductivity values (ksat) were determined. For FC fibers, an increase in fiber dosage caused ksat values to increase by 9.5% and 94.3% for the 6 and 12 mm lengths, respectively, at all confining pressures and curing periods. For FM fibers, ksat values for samples mixed with 6 mm fiber increased by 12 and 99.2% for 6 and 12 mm lengths, respectively for all confining pressures at the end of the 28-day curing period. The results obtained from a flexible wall permeameter (FWP) were compared with those of a rigid wall permeameter (RWP) available in the literature, and the fundamental mechanism responsible for such variations is explained.

Mercury vertical and horizontal concentrations in agricultural soils of a historically contaminated site: Role of soil properties, chemical loading, and cultivated plant species in driving its mobility

The long term vertical and horizontal mobility of mercury (Hg) in soils of agricultural areas of a historically contaminated Italian National Relevance Site (SIN Brescia-Caffaro) was investigated. The contamination resulted from the continuous discharge of Hg in irrigation waters by an industrial plant (Caffaro S.p.A), equipped with a mercury-cell chlor-alkali process. The contamination levels with depth ranged from about 20 mg/kg dry weight (d.w.) of soil in the top (plow) layer to less than 0.1 mg/kg d.w. at 1 m depth. The concentrations varied also spatially, up to one order of magnitude within the same field and showing a decreasing trend from the Hg source (i.e., irrigation ditches). The concentration profiles and gradients measured were explained considering Hg loading, soil properties, such as the texture, organic carbon content, pH and cation exchange capacity. A Selective Sequential Extraction (SSE) was also applied on soil samples from an ad hoc greenhouse experiment to investigate the role of different plant species in influencing Hg speciation in soils. Although most of the extracted Hg was included in scarcely mobile or immobile forms, some plant species (i.e., alfalfa) showed to importantly increase the soluble and exchangeable fractions with respect to the unplanted control soils, thus affecting mobility and potential bioavailability of Hg.