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The enhanced electrokinetic (EK) technique is an innovative approach and increasingly used in remediation of the fine-grained texture soils contaminated with different types of contaminant. In this study, the EK is enhanced by adding an intermediate compartment and using purging solutions at the electrode's compartments. The natural clayey soil samples were obtained from Al-Ahadab oil field and artificially contaminated with two ratios of copper sulfate (66666.67 and 26666.67 mg/kg). The feasibility of using EK technique was evaluated by the efficiency of extracting copper from soil and the magnitude of recovery in the geotechnical properties of soil. The duration of remediation was continued for about 240-250 hours depending either on the continuity of electroosmosis flow or reach a constant rate of electrical current. The removal efficiency of copper from contaminated soil samples was ranged from 98.4% to 99.6%. The EK remediation technique proved a marginal impact on the specific gravity and Atterberg's limits, but it has a significant effect on the shear strength parameters and compressibility of soil. Furthermore, the EK technique can be considered an efficient method for removing the low and high concentrations of copper sulfate from clayey soil of low permeability. [ABSTRACT FROM AUTHOR]

The main goal of this research is to carry out an analysis of the influence of rainfall on the stability of the slope downstream of a homogeneous earth dam, with a 15-meter embankment height and drainage at the foot of the slope. A sample of 10 unsaturated clayey soils was determined to form the embankment, and rains were applied for 12 and 24 hours, for return periods of 5, 10, 25 and 50 years. The behavior of the safety factor and the failure time are evaluated. In addition, the influence of porosity and permeability of soils on stability is determined. [ABSTRACT FROM AUTHOR]

The deep soil mixing (DSM) method is used to improve the mechanical and/or hydraulic properties of soils. The DSM method refers to an in situ mixing of soil, water, and hydraulic binder without excavation. After describing the specific microstructure of DSM materials compared with soils or concrete, four porosity–permeability analytical models from literature and based on microstructural parameters (i.e., porosity and pore-size distribution derived from mercury intrusion porosimetry) were applied to predict the water permeability (K) of soil–cement mixtures. After comparing the estimated permeabilities (Kest) with the experimental measurements of such a parameter (Kexp) using a triaxial cell, an indicator parameter A (=Kest/Kexp) was proposed to evaluate the ability of each model to fit the water circulation in DSM material. By calculating the average ratio 〈A〉 from the 24 materials in the studied database, three of the four applied models satisfactorily estimated the water permeability of the studied DSM materials. To reach an 〈A〉 value closer to 1, an extension of the Aït-Mokhtar's model, initially developed for cementitious mortars, was proposed by considering the specificities of the DSM materials. If previous models used only the contribution of nanopores less than 100 nm to the water flow, the extended model considered the contribution of all pore populations in the permeability calculation. Such an approach resulted in a significant improvement in the matching between the calculated and measured permeabilities. [ABSTRACT FROM AUTHOR]

The earliest method of waste disposal is dumping waste in landfills. The important component of landfills which prevents the passage of leachate to the subsoil is defined as the bottom liner. A landfill liner must contain a specific range in terms of swelling behavior, strength, and permeability before placing down beneath the constructed landfills. The present paper summarizes the detail of the different materials and their feasibility which satisfy the criteria to be used as landfills liner. The detail of findings of microstructural analysis (SEM–EDX, XRD, FT-IR, etc.) along with the waste materials which compact the particles and enhance the strength and stability of soils is also discussed. A lot of landfill liner materials such as Bentonite, sand, fly ash, cement, biochar, marine clay, lateritic soil, and geosynthetics have been used to enhance the geotechnical properties of liners. Among all, geosynthetic clay liner (GCL) and compacted clay liner (CCL) show increased hydraulic conductivity for clay soil with high plasticity whereas this value reduces for clayey soil having low plasticity with the increase in the concentration of the salt solution. The hydraulic conductivity of the mix containing biochar, bentonite, and sand is found to be 1 × 10−9 m/s. The hydraulic conductivity and shear strength of the soil increases while the compressibility of the soil decreases with an increase in the biochar percentage having smaller particle size. Also, the alkaline activator is suggested to be best for soil stabilization as compared to standard Portland cement. The development of new materials must be environmentally sustainable and should contain sufficient shear strength so that it can sustain the overburdened load of dumped waste. It should also be free from cracking so that the contamination of subsoil and groundwater can be minimized. [ABSTRACT FROM AUTHOR]

Consolidation and creep are two types of time-dependent deformation of clay soil. However, the soil deformation presents probabilistic behaviours when the spatial variability is considered. The Monte–Carlo method is used to sample anisotropic random fields that are mapped into two-dimensional random finite element models (RFEM) to analyse the influences of spatial variability on the time-dependent deformation of clay soil. The anisotropic random fields of soil parameters are generated by a spectral representation method (SRM) to describe the spatial variability of clay soil. The consolidation and the creep problems are modelled by Biot's consolidation theory and the creep model proposed by Yin et al. (2010) respectively. The spatial variability of Young modulus and permeability coefficient in probabilistic consolidation analysis and the secondary consolidation coefficient in probabilistic creep analysis are emphasized by the RFEM simulation. The results show that the scale of fluctuation (SOF) in vertical direction and the coefficient of variation (COV) of Young modulus and permeability have significant influences on the probabilistic characteristics of consolidation behaviour. Besides, the bunched region of low permeability soil produces a blockage effect, which seriously affects the consolidation characteristics. It is found that the uncertainty of creep deformation will accumulate over time until it remains constant. The variability of creep deformation increases with the increase in the vertical SOF and COV of the secondary consolidation coefficient. The research also provides insightful clues for the time-varying reliability design related to the time-dependent deformation of clay soil. [ABSTRACT FROM AUTHOR]

Petroleum products influence the engineering behaviour of the soil. Neogene clays and glacial tills from Central Poland were tested under laboratory conditions to evaluate the changes of selected physical and mechanical parameters: particle size distribution, particle density, swelling, shear strength and permeability. Four petroleum products were used in the experiments: diesel fuel, kerosene, jet fuel and mineral engine oil. The study revealed that even for the lowest degree of contamination the values of physical and mechanical properties of the soils changed significantly. Greater variation can be expected in soils contaminated with high-viscosity compounds. Also, higher relative changes were found for glacial tills than for Neogene clays. Consolidation tests revealed changes in soil permeability depending on the soil composition and the physical properties of the contaminant - considerable reduction of permeability was observed for glacial tills contaminated with light Jet fuel, while the reduction was lower for Neogene clays. The obtained results indicate the role of mesopores and the dimensionless pore pressure coefficient in changes of soil permeability. The methodological issues regarding testing and analysing the hydrocarbon-contaminated soils were also presented and discussed, which might be useful for researchers studying contaminated soils. [ABSTRACT FROM AUTHOR]

Compost amendment is a widespread agronomic practice, but little information is available about the short- and medium-term effects on clay soils. In this investigation, we selected three soil compost rates (treatments, T), i.e., fertilizer (T2 = 1.5 kg m−2), amending (T3 = 15 kg m−2), and organic (T4 = 75 kg m−2), that were compared to a control (T1). Our research accounts for the effects reached on representative large boxes (about 0.75 m3), without crops and for about eighteen months. An overall assessment of the physical and hydraulic properties of the soil was made, including infiltration rate or saturated hydraulic conductivity (Ks), water content and water retention (θ) of the soil, bulk density and structure, and several physical quality indicators obtained from the water retention curve, accounting for the optimal balance between water/air into the soil, pore volume distribution function, and soil features in the inflection point of the soil water retention curve. Additionally, the temporal changes of Ks were evaluated. The main results showed that (i) after eighteen months, and regardless of T, θ significantly improved by a factor of 1.2–1.3, but these improvements (up to 1%) were detected only close to water saturation (i.e., until 6 cm of soil pressure head) when little (T2) or no compost (T1) addition was considered, while a larger range was detected (until 60 cm) when higher rates (T3–T4) were used; (ii) Ks determination allowed to establish that compost effects vanished after about eleven months, but it was not possible to verify that composting increased the permeability of the investigated clay soil within that time frame; (iii) some significant correlations between Ks and some soil physical indicators estimated from both the inflection point of the water retention curve or bulk density suggested possible improvements in soil permeability. Because some factors (water content of the soil above all) could have affected the comparison of Ks measurements, further research on this topic is needed. [ABSTRACT FROM AUTHOR]

• A modified permeability testing device is developed to test the permeability of subgrade soil under the overlying stress. • The hydraulic characteristics model, considering the influence of stress and wetting-drying cycles, is established. • A method, repaid obtaining the water migration law of subgrade under stress and wetting-drying cycles, is developed. The wetting–drying cycles and overlying stresses experienced by unsaturated subgrade alter soil pore structure, resulting in variations in its hydraulic characteristics, ultimately affecting subgrade water migration and moisture distribution. However, the combined effects of these two phenomena on key subgrade hydraulic characteristics including the soil–water characteristics and the permeability property remain unclear. This paper aimed to experimentally measure soil–water characteristic curve (SWCC) and saturated permeability of subgrade soil under various overlying stresses and wetting–drying cycles. A customized SWCC measurement system and a modified permeability testing device were developed to conduct the test program on compacted silty clay soil specimens. Subsequently, the influence of overlying stress and wetting–drying cycles on the hydraulic characteristics of the subgrade was analyzed, with a focus on the SWCC and saturation permeability coefficient, and the corresponding fitting model is established. Finally, the water transfer behavior of subgrade considering the effect of wetting–drying cycles and overlying stresses was analyzed using finite element method (FEM). The results indicated that an increased number of wetting–drying cycles and higher overlying stress led to a decrease in the saturated moisture content of subgrade soil, an increase in the air-entry value, and a flatter SWCC. The saturation permeability coefficient increased with the number of wetting–drying cycles, but decreased with increasing overlying stress. Furthermore, a high correlation was observed between the SWCC and permeability coefficient predictive model, considering both the number of wetting–drying cycles and overlying stress. Lastly, when considering the stress state and wetting–drying cycles, significant differences in the evolution of matric suction of the subgrade during rainfall were observed. The overlying stress amplifies the decrease in matric suction of the soil above the subgrade, while wetting–drying cycles reduce this decrease. [ABSTRACT FROM AUTHOR]

The fact that the permeability and microstructure properties of clay will be changed by NAPL (Nonaqueous Phase Liquids) pollution draws high attention in the study of the interaction between NAPL and contaminated soil. Through in-field contaminated clay soils from vinyl chloride and 1, 1, 2-trichloroethane-contaminated site in Shanghai, the variation of the content of vinyl chloride and 1, 1, 2-trichloroethane pollutants in clay with depth was obtained. The change of plasticity, permeability, and microstructure properties of the clay samples contaminated by vinyl chloride and 1, 1, 2-trichloroethane were investigated in detail. The measured test results were compared with the uncontaminated clay and indoor soaked contaminated clay samples by TCE (Trichloroethylene). The test results showed that the microstructure characteristics of clay were changed under the influence of the content of TCE, vinyl chloride, and 1, 1, 2-trichloroethane. The total porosity, accumulative pore volume, and the content of the macroporosity percentage of clay soils showed an increasing trend. The flocculation structure of contaminated clay samples was observed, but there were no overhead pores and connected cracks. Volatile organic pollutants were detected in both field and indoor contaminated clay samples. The plastic limit and liquid limit of each layer of contaminated samples decreased slightly, the plastic index did not change significantly, and the pore ratio and permeability coefficient increased gently. At the same time, the clay shrinkage was aggravated by TCE pollution, and cracks appeared on the surface of soil samples. However, no connected cracks were formed. Test results indicated that the self-developed improved permeability test device can be used to test the permeability coefficient of clay samples with shrinkage and to crack by NAPL pollution. The permeability coefficient showed an increasing trend, though the increase was not at the level of magnitude. [ABSTRACT FROM AUTHOR]

This paper attempts to study the effects of acidic and alkaline waters on the geotechnical properties of a particular type of clay with low plasticity from the northeast areas of Isfahan that have been evaluated with pH values adjusted from 3 to 8. The remoulded specimens were placed in moulds under the influence of acid and alkaline rains with different pH values and years of precipitation. Atterberg limits tests, soil permeability coefficient, California bearing ratio (CBR) test and unconfined compressive strength (UCS) of soil specimens with various pH values were used to evaluate soil mechanical changes relative to soil with neutral acidity. In order to identify internal structural mechanisms of soil before and after artificial raining on the specimens, scanning electron microscopy and pH drainage tests of specimens were performed. The results of the interaction of rain and soil with shifting from neutral values were evaluated over a period of precipitation fluxes from 1 to 20 years. In overall, the more is the acidity or alkalinity of the artificial rain, the more will increase the Atterberg limits and the soil permeability compared to the soil specimens under artificial rain with pH = 7; and the decreasing trend is observed in UCS values and CBR. [ABSTRACT FROM AUTHOR]

The application of stabilised soil in agricultural construction works such as shallow foundation fills and subgrade material for farm roads is in demand due to the improved geotechnical properties. This study focused on improving the compressive capabilities and the permeability characteristics of rice husk ash (RHA)-treated clayey soils using basalt fibre. Basalt fibres are made from naturally occurring basalt rock, yet their use in soil stabilisation has not been realised due to limited research for its validation in ground stabilisation. Essential variables in the stabilised soil matrix included basalt fibre length (3 mm, 6 mm, and 12 mm), RHA percentages (5%, 10%, and 15%), and cement percentage (3%). In addition, the optimum moisture content of each admixture was determined by standard proctor compaction tests and reduced by 3% to prepare the specimens for unconfined compression strength test, constant head permeability test, and scanning electron microscope (SEM) test. It was observed that the unconfined compression strength of the RHA-basalt fibre stabilised clayey significantly increased when the specimens wet cure for 28 days. Similarly, adding fibres into the soil improved the permeability coefficient. The SEM test showed a porous morphology that increased permeability. Furthermore, through SEM, the randomly oriented basalt fibres' portrayed the reinforcing phenomenon related to improved compressive strength and sufficient bearing capacity to support structures built upon this class of soils. [ABSTRACT FROM AUTHOR]

Soil structure is a key factor to determine the different functions of soil, such as water infiltration and retention, soil permeability, and nutrients availability. The dynamic behavior of soil also depends mainly on the tillage, crop roots, and soil organic matter return. Black soil is one of the most important arable soil with high clay content, but hard soil structure is one of the main factors limiting crop growth. It is still lacking on the effect of organic amendment on soil pore structure in the black soil. In this study, a field experiment was carried out in the black soil region located in Hailun City, Heilongjiang Province of China, in order to clarify the effects of organic amendment and depths on soil physical properties and pore structure before maize sowing in 2019. Four treatments were conducted using random block design with four replicates, including shallow tillage with maize straw return in 0-15 cm soil layer (T1), deep tillage with maize straw return (T2), or combined maize straw and organic manure return (T3) in 0-35 cm soil layer, conventional tillage without organic amendment as control. Maize straw and organic manure were also incorporated into the soil layers by shovel using manual work, where the application rates were 10 000 and 30 000 kg/hm2, respectively. CT scanning was adopted to visualize and quantify soil pore structure after maize harvesting. The constant head method was used to measure the saturated hydraulic conductivity. The results demonstrated that the bulk density under T1, T2, and T3 treatments significantly decreased 3.77%-5.66%, compared with CK, while the saturated hydraulic conductivity increased by 2.2-5.00 times, and the field water capacity increased by 6.91%-11.01% within 0-15 cm soil layer (P<0.05). T2 and T3 treatments also improved the bulk density, saturated hydraulic conductivity, and field water capacity within >15-35 cm soil layer after one maize growing season. Furthermore, the number of soil pores and porosity of >500 μm aperture under T1, T2, and T3 treatments significantly increased by 18.1%-180% and 69.2%-256% (P<0.05) in 0-15 cm soil layer, respectively, compared with CK treatment (P<0.05). Specifically, the soil pore number and porosity of >1 000 μm aperture were more 6.06%-150% and 17.4%-196% under T2 treatment than the rest. It infers that the treatments with organic amendment increased the number of soil pores with optimal distribution. In addition, the complexity and connectivity of soil pore also increased significantly, in presence of connected and sender pore. The Euler number values under T1, T2, and T3 treatments were decreased by 21.7%-54.3%, whereas, the fractal dimension under T1 treatment increased by 1.5% in 0-15 cm soil layer (P<0.05), compared with CK treatment. T2 and T3 treatments improved the soil pore structure in >15-35 cm soil layer, as shown in that the Euler decreased by 65.9%-70.5%, anisotropy, fractal dimension, and circularity increased by 50.0%-110%, 12.8%-13.9%, and 12.2%-14.9%, respectively, compared with CK treatment (P<0.05). The Euler and porosity of >1 000 μm aperture presented the largest contribution both for the bulk density and saturated hydraulic conductivity in 0-35 cm soil layer, whereas, the anisotropy and Euler presented the largest contribution for the field capacity in 0-15 cm and >15-35 cm soil layers. Pearson correlation analysis indicated that the extremely significant negative relationship was found between bulk density and saturated hydraulic conductivity, field water capacity, soil porosity within 0-15 cm soil layer (P<0.01), while the extremely significant or significant correlation was found between bulk density and all indicators, excepting for the anisotropy and Euler. Consequently, the improved physical properties of soil were attributed to the fact that the organic amendment regulated soil structure, including optimal distribution of soil pore, complex, and connectivity of pore structure. Correspondingly, the organic amendment can be expected to serve as an effective approach for the pore structure of black soil. It is also necessary to consider the response of soil pore structure in the decomposition of returned organic manure in the future. [ABSTRACT FROM AUTHOR]

Soil hydraulic conductivity is a geotechnical parameter commonly used in civil engineering works. It is necessary when designing an underground drainage system. There are two main approaches for determining and interpreting this parameter: in situ tests (example of the Porchet test) and laboratory tests (permeameter test). However, the results obtained through these two methods are generally not identical. The purpose of this work is to assess the permeability coefficient of Broukou and Kpassidè clay soils (two (2) localities in northern Togo), using the Porchet test and the variable load permeameter test. It turns out that the Porchet method on clay soils gives permeability results of the order of 102 times higher than those obtained with the variable load permeameter test carried out in laboratory. [ABSTRACT FROM AUTHOR]

Existing electro-osmotic calculation models are mostly based on the assumption of a porous medium with uniform pores, whereas natural soil has pores of different sizes. This is especially significant in the case of low-permeability soil, whose pore size can vary over five or six orders of magnitude, from the nanometre to the millimetre scale. Experimental results have revealed significant differences in the electro-osmotic flow characteristics of soils with various pore sizes, indicating a strong dependence on pore size distribution (PSD). This dependence is termed the pore size effect (PSE) on electro-osmosis. In this paper, a series of one-dimensional electro-osmosis experiments on three types of low-permeability clay soil are conducted to quantify the PSE on electro-osmosis. Based on the experimental results and an analysis of electro-osmotic characteristics, a modified analytical approach considering the actual soil PSD and its effect on electro-osmosis is proposed and thereby two modified analytical models are established. Using the experimental results, the modified models are compared with the existing Helmholtz–Smoluchowski model and other models that assume uniform pores. The results show that the PSE increases with increasing thickness of the electric double layer and that the modified models can be used to reasonably calculate the electro-osmotic permeability of low-permeability soil. [ABSTRACT FROM AUTHOR]

Soil hydraulic conductivity is a geotechnical parameter commonly used in civil engineering works. It is necessary when designing an underground drainage system. There are two main approaches for determining and interpreting this parameter: in situ tests (example of the Porchet test) and laboratory tests (permeameter test). However, the results obtained through these two methods are generally not identical. The purpose of this work is to assess the permeability coefficient of Broukou and Kpassidè clay soils (two (2) localities in northern Togo), using the Porchet test and the variable load permeameter test. It turns out that the Porchet method on clay soils gives permeability results of the order of 102 times higher than those obtained with the variable load permeameter test carried out in laboratory. [ABSTRACT FROM AUTHOR]

Soil hydraulic conductivity is a geotechnical parameter commonly used in civil engineering works. It is necessary when designing an underground drainage system. There are two main approaches for determining and interpreting this parameter: in situ tests (example of the Porchet test) and laboratory tests (permeameter test). However, the results obtained through these two methods are generally not identical. The purpose of this work is to assess the permeability coefficient of Broukou and Kpasside clay soils (two (2) localities in northern Togo), using the Porchet test and the variable load permeameter test. It turns out that the Porchet method on clay soils gives permeability results of the order of 102 times higher than those obtained with the variable load permeameter test carried out in laboratory. [ABSTRACT FROM AUTHOR]

Chemical stabilization is defined as modification of engineering properties of soil with chemical reactions of various additives. Chemical stabilization is applied to the soils which cannot be adequately treated by mechanical stabilization. Chemical stabilization leads to changes in soil properties such as strength, plasticity, compaction and durability, as well as in its permeability. Permeability of soil is important in ground water flow and leakage problems. However, there are few studies about the effect of chemical stabilization on permeability. In this study, the effects of chemical stabilization with lime and perlite combinations on permeability of high plasticity clayey soil were investigated. With the stabilization of high plasticity clayey soils with lime, the permeability of the mixture increases up to 25 times. Moreover, perlite which can be used as a secondary additive in stabilization of such soils causes serious decrease in permeability. [ABSTRACT FROM AUTHOR]

The effect of high concentration sodium salt solution infiltration in reclaimed water on soil hydraulic characteristics is one of the key problems of soil ecological environment degradation caused by long-term low-quality water irrigation. In this paper, the hydrodynamic parameters of 5 kinds of subtropical soil, such as clay fluvo aquic soil, sandy fluvo aquic soil, red soil, paddy soil and purple soil, were measured by constant head penetration method and one-dimensional horizontal soil column imbibition method. The influence of sodium salt solution concentration on the hydraulic properties of soil was investigated, and the mechanism of the physical and chemical properties of soil affecting the hydraulic conductivity was analyzed. The results showed sodium slat solution infiltration could enhance soil wet front migration rate of clay fluvo aquic soil, sandy fluvo aquic soil and paddy soil maximally by 33.0%, 32.5% and 93.5%, lower that of red soil maximally by 34.8%. The soil clay content, exchangeable iron and aluminum content mainly inhibited soil water movement, while silt content, exchangeable calcium and magnesium content promoted soil water movement. Sodium salt accelerated water movement in clay fluvo aquic soil, sandy fluvo aquic soil and paddy soil. Relative soil water diffusivity increased by 22.0%, 37.3% and 39.7% respectively. Sodium salt inhibited the water diffusion of red soil and purple soil. The higher salt concentration could result in the smaller relative soil water diffusivity. At 15 g/L salt concentration, the soil water diffusivity decreased by 30.5% for red soil and 42.1% for purple soil, respectively. Relative soil water diffusivity of clay fluvo aquic soil, sandy fluvo aquic soil, red soil and purple soil fluctuated with the increase of soil water content, while the relative soil water diffusivity of paddy soil decreased with the increase of soil water content. Relative soil water diffusivity of paddy soils showed a good parabolic relationship with salt concentration (R²=0.987), while red soils and purple soils showed a good linear relationship with salt concentration (R²>0.933). The saturated hydraulic conductivity of clay fluvo aquic soil treated with sodium salt solution increased most obviously, with a maximum increase of 77.3%, followed by paddy soil, with a maximum increase of 25.1%. With the increase of salt solution concentration, the relative saturated hydraulic conductivity of soil decreased first and then increased. In the range of 1-10 g/L salt concentration, the saturated hydraulic conductivity of soil had a good parabolic relationship with the sodium salt concentration (R² was not less than 0.807), and the saturated hydraulic conductivity of soil was the smallest when the concentration of each extreme point of soil was about 5 g/L. Therefore, the salt concentration of reclaimed water should be moderately controlled to a level lower than the extreme point concentration. [ABSTRACT FROM AUTHOR]

The main issue of the paper is the estimation of soil hydraulic permeability based on the DMT test. DMTA, DMTC and SASK methods performed in the Nielisz dam, Stegny and the SGGW Campus of the Warsaw University of Life Sciences sites are described. The article presents the implementation of the dilatometer Marchetti test (DMT) in the determination of soil fraction and effects of its occurrence in the subsoil, tested in the Nielisz dam located in the Wieprz river valley in the Lublin province, and in various sites in Warsaw (Stegny site and SGGW Campus of the Warsaw University of Life Sciences). In order to acquire the needed data, the flat dilatometer test (DMT) method was used. A direct and indirect pressure methodology of interpreting soil swelling was characterized in the article. The paper shows the possibilities of determining sand, silt and clay soil fractions based on po and p1 pressures from dilatometer tests (DMT) and the effective (σ'vo) and total (σvo) vertical in situ overburden stress. Additionally, the main advantage of this paper is the proposal of use of a new chart to determine hydraulic permeability and soil fraction, based on DMT tests. [ABSTRACT FROM AUTHOR]

Biochar has not been adequately used by farmers to improve the clay textured soil productivities in the world. Therefore, the objective of this study is to investigate the effect of the co-application of biochar with different rates of phosphorus (P) fertilizer on selected soil physical properties and wheat yield on clay textured soil over two growth seasons. Biochar treatments occupied the main plots at a rate of 0.0 and 10 t ha−1, while the sub-plots were devoted to phosphorus rates at rates of 0%, 50%, 100%, and 150% of recommended P fertilizers. Biochar (10 t ha−1) and P at different rates decreased soil bulk density significantly. Meanwhile, it increased aggregate stability, saturated hydraulic conductivity and soil water retention significantly at (p <.05), and it improved the grain yield of wheat. More grain yields in the soil treated with biochar than untreated soil under all P application rates for both years were probably caused partially by more nutrients (N, P, and K) were applied from biochar itself. Grain yield of wheat in the soil-amended biochar and P did not increase significantly between the application at 50%, 100% and 150% P. The results of this study indicate that phosphorus blends with biochar can be used to decrease the bulk density of clay textured soils and to improve crop production in these soils. [ABSTRACT FROM AUTHOR]

Irrigation water containing appreciable amount of magnesium (Mg) is increasingly used in farming. However, studies on the effect of Mg on soil permeability and structural stability are limited and the results are contradicting. In this study, four soils of different dominant clay mineralogy, specifically kaolinite, illite and montmorillonite, were used to investigate the effect of Mg on saturated hydraulic conductivity (K sat), interaction with organic carbon and soil clay dispersion and to compare to the effect of Ca. The soils were packed in columns and leached with four groups of either Ca-Ca, Ca-Mg, Mg-Mg or Mg-Ca solutions at the successive concentrations of 0.5, 0.25, 0.1, 0.05, 0.025, 0.01, 0.005, 0.001 and 0.0001 M, and finally with deionised water. K sat was measured and leachates were assessed for dissolved organic carbon (DOC) and dispersion as turbidity. The leached soils were tested for aggregate stability, mechanical dispersion and zeta potential. This study showed that Mg had a disaggregation effect on soil structural stability. As compared to Ca, K sat on Mg treated cores were lower over a wide range of concentrations, desorption of DOC and turbidity from Mg clay surface was higher, although the dispersion in leachates was insignificant under both Mg and Ca treatments. The effect of Mg treatment was more pronounced on smectic and illitic soils. The decrease in K sat was related to Mg induced disaggregation, due to intra-crystalline swelling and/or the inter-crystalline swelling in Mg treated soil clays. • Mg had a disaggregation effect on soil structural stability. • Mg reduces K sat as compared to Ca. • DOC from Mg leached samples is greater than that from Ca leached samples. [ABSTRACT FROM AUTHOR]

Unsaturated soils permeability ( K unsat ) is a required parameter when modeling water flow and transport processes in the subsurface. Having highly nonlinear relationship with volumetric water content (θw) and suction (S), the value of K unsat varies by several magnitudes when moving from clayey to gravel soils. On the other hand, determination of K unsat is very difficult, costly, and time consuming. Recently, adaptive neuro-fuzzy inference system (ANFIS) has been used for modeling and prediction of such complex and nonlinear problems. Investigated in this paper is the capability of ANFIS for modeling K unsat . The database used in ANFIS modeling is collected from SoilVision. This database contains 4347 K unsat test records on 245 soil types collected from all around the world; it approximately covers triangular chart defined by US Department of Agriculture System for classifying mixed soils. In order to get the optimum number of ANFIS training epochs and ANFIS structure, trial and error method was used. To check the predictive capacity of the ANFIS model, several statistics such as determination coefficient (R2), Root Mean Square Error, Mean Absolute Error and Variance Account For were calculated. The results demonstrated that the ANFIS model can be successfully applied for prediction of K unsat . [ABSTRACT FROM AUTHOR]

Unsaturated soils permeability ( K unsat ) is a required parameter when modeling water flow and transport processes in the subsurface. Having highly nonlinear relationship with volumetric water content (θw) and suction (S), the value of K unsat varies by several magnitudes when moving from clayey to gravel soils. On the other hand, determination of K unsat is very difficult, costly, and time consuming. Recently, adaptive neuro-fuzzy inference system (ANFIS) has been used for modeling and prediction of such complex and nonlinear problems. Investigated in this paper is the capability of ANFIS for modeling K unsat . The database used in ANFIS modeling is collected from SoilVision. This database contains 4347 K unsat test records on 245 soil types collected from all around the world; it approximately covers triangular chart defined by US Department of Agriculture System for classifying mixed soils. In order to get the optimum number of ANFIS training epochs and ANFIS structure, trial and error method was used. To check the predictive capacity of the ANFIS model, several statistics such as determination coefficient (R2), Root Mean Square Error, Mean Absolute Error and Variance Account For were calculated. The results demonstrated that the ANFIS model can be successfully applied for prediction of K unsat . [ABSTRACT FROM AUTHOR]

• A new method to simultaneously estimate soil hydraulic properties is presented. • K s , α and n are estimated from inverse analysis of an upward infiltration curve. • The method is evaluated on different synthetic and experimental soils. • Accurate estimates of K s , α and n are obtained in the theoretical curves. • The method allows accurate estimates of K s and n in all experimental soils. This paper presents a new laboratory method to simultaneously estimate K s and α and n parameters of the van Genuchten (1980) θ (h) from the inverse analysis of an upward infiltration curve measured in a 5-cm high soil column. The method was evaluated on synthetic 1D infiltration curves generated for a theoretical loamy sand, loam and clay soil. The influence of the soil initial condition on the inverse analysis was also studied. Next, an optimization method was presented and tested on eight theoretical soils (from loamy sand to clay). The method was subsequently applied to experimental curves measured on five sieved soils (from sand to clay) packed in 5-cm high and diameter cylinders. The K s , α and n values estimated from the inverse analysis of the experimental curves were compared to those measured by Darcy and the pressure cell method (PC). The initial soil tension, h i , which had an important influence on the optimization, was fixed to −6.0·105 cm. The optimization method resulted robust and allowed accurate estimates of the actual hydraulic parameters. A close to one relationship (R2 = 0.99) was observed between the theoretical K s , α and n and the corresponding values obtained with the inverse analysis. Regarding to the experimental soils, significant relationships close to one were obtained between K s and n (R2 > 0.98) estimated from inverse analysis and those measured with Darcy and PC. A non-significant relationship with slope away from one was found for α. [ABSTRACT FROM AUTHOR]

Abstract Soil water repellency affects vast regions of agricultural and native land across the globe. Sandy soils are most likely to develop non-wetting characteristics with susceptibility decreasing with clay content. This study uses molecular dynamics simulations combined with laboratory scale experiments to study the interactions and assembly of saturated C 16 straight chain alcohol and carboxylic acid molecules on a range of soil surfaces. The development of severe water repellency on sand at low loading levels of palmitic acid (0.75 × 10−6 mol g−1) is explained in terms of favourable H-bonding with silica surfaces and the development of 2–3 layers of lateral aligned organic molecules on the mineral surface. The efficacy of kaolinite in lowering soil water repellency is attributed to the higher surface area of this mineral and favourable surface chemistry, which hinders formation of persistent organic multilayers. Highlights • Molecular dynamics simulations identify interactions of fatty acids on sand and clay. • H-bonding interactions between the molecules and surfaces differ for clay and sand. • A parallel arrangement of molecules with the mineral surfaces is kinetically favourable. [ABSTRACT FROM AUTHOR]

Gegenwärtig diskutierte Phänomene, wie häufig auftretender Oberflächenabfluss, vermehrte Bodenerosion und verringerte Ertragssicherheit, lassen sich ansatzweise über Bodenstruktureigenschaften und eine daraus hervorgehende, räumlich unterschiedlich gesättigte Wasserleitfähigkeit des Bodens erklären. Hierzu wurden Datensätze aus 766 Profilen unter Acker- und Grünlandnutzung in den vier Hauptnaturräumen Schleswig Holsteins (Östliches Hügelland, Niedere und Hohe Geest sowie Marsch) zur gesättigten Wasserleitfähigkeit (kf) in vertikaler und horizontaler Richtung und damit deren Richtungsabhängigkeit (Anisotropie) bis in eine Tiefe von 60 cm untersucht. Die Ergebnisse zeigen eine verstärkte Anisotropie der kf in horizontaler Richtung an, die jedoch in Abhängigkeit vom geologischen Ausgangsgestein, Bodentyp und Tongehalt sowie von der Landnutzung variiert. Unter Ackernutzung weisen die Unterböden aller Hauptnaturräume im Mittel eine horizontale Anisotropie auf, die unterhalb der Pflugsohle (≤ 40 cm Tiefe) am stärksten ausgeprägt ist und auf Plattenstrukturbildungen als Folge der Bodenbewirtschaftung hindeuten. Unter Grünlandnutzung zeigen besonders die Oberböden eine horizontale Anisotropie, wobei diese in den beiden Geestregionen mit einem hohen Anteil an Viehwirtschaft auch im Unterboden sehr ausgeprägt ist. Anisotropieeffekte, insbesondere im Unterboden unter Ackernutzung, deuten sich auch bodentypspezifisch für Kolluvisole, Pseudogley-Parabraunerden und Pseudogleye an. Deren hohe Empfindlichkeit gegenüber anthropogenen Strukturänderungen (Plattenbildung) spiegelt sich im zeitlichen Verlauf der horizontalen kf wider, die über die letzten 30 Jahre im Östlichen Hügelland signifikant zugenommen hat. Summary: Currently discussed phenomena like more frequent surface runoff after heavy rainfall events, increasing soil erosion and reduced yield stability can be explained to some extent by soil structure properties and a resulting, spatially differing saturated hydraulic conductivity of the soil. For this purpose, samples from 766 soil profiles under arable and grassland use in the four major natural environments of Schleswig-Holstein (Weichselian glacial area, Higher and Lower Geest, Marshland) were taken and, inter alia, the saturated hydraulic conductivity in vertical and horizontal direction and thereby its directional dependency (anisotropy) was evaluated down to the 60 cm depth. The results prove an enhanced anisotropy of the hydraulic conductivity in horizontal direction, with variations depending on the parent material, soil type and clay content, as well as the land use. The subsoils under arable land exhibit a horizontal anisotropy that is most distinct below the plow pan (≤ 40 cm depth) and can be explained by the development of a platy soil structure as a consequence of the management (tillage). Soils under grassland use exhibit a horizontal anisotropy mainly in the topsoils, whereby it is additionally very pronounced in the subsoils of the two Geest regions with a high percentage of dairy farming. Such anisotropy effects, especially in the subsoils under arable land use, can be determined soil type specifically for the representative soils of the Weichselian glacial area: Anthrosols ("Colluvic"), Stagnic Luvisols and Stagnosols. The chronological sequence of the horizontal hydraulic conductivity mirrors their high sensitivity against anthropogenic soil structure changes (development of plates), which have clearly increased in the Weichselian glacial area during the latest 30 years. [ABSTRACT FROM AUTHOR]

Intense mechanization during forest harvesting and timber extraction degrades soil structure and affects pore functioning, but no studies have clearly distinguished the response of composition and functional soil properties to pine harvest in a subtropical environment. This paper describes the effect of mechanized harvesting of Pinus taeda L. on compaction and pore functioning of two subtropical Alfisols intensively used for commercial forest production in southern Brazil. The study was conducted in a 17-year old commercial forest of P. taeda on clay and sandy clay Hapludalf soils. Soil conditions tested were a control, i.e., before harvesting (BH); after tree felling (AF) in the full tree system; after timber dragging with one skidder pass (A1P); after timber dragging with three skidder passes (A3P); and after timber removal from stocking yard (TY). We evaluated composition (bulk density, degree-of-compactness, total porosity, and macroporosity) and functional (saturated hydraulic conductivity, precompression stress, compressibility coefficient, and penetration resistance) soil properties. The results show the upper soil layer is the most vulnerable to compaction, which significantly impairs pore functioning. Nevertheless, machine wheeling may affect subsurface layers (down to at least 0.40 m, as tested herein) depending on soil type, moisture and structure. Three passes of the skidder resulted in greatest degree-of-compactness, high bulk density, low macroporosity (below the critical level), reduced hydraulic conductivity (nearly water impermeable), and increased resistance to penetration (above the critical limit of 2 MPa). Pine harvest residues (9.8–15.6 Mg ha −1 , corresponding to 7.3–8.2 cm height) were insufficient to dissipate stress applied by skidder intense wheeling. We show planning of harvesting activities must consider reducing traffic intensity and/or establishing permanent traffic routes to ensure minimum damage on forest soils, particularly on their functional soil properties. [ABSTRACT FROM AUTHOR]

A snowpack is known to affect landslide stability as the snow loading changes. Furthermore, the snowpack can have effects on the hydrological behavior in the landslide mass. To clarify the response of pore water pressure to snow loading, continuous field-based monitoring of hydraulic and meteorological factors in landslides was conducted for a deposit of extremely low-permeability “quick clay” in Mid-Norway. The pore water pressure increased during every snow-covered period. The pressure exhibited little response to meltwater and/or rain, but corresponded closely to changes in snow accumulation. The increase in pore water pressure during the snow-covered period was considered to be excess pore water pressure generated by undrained snow loading on the extremely low-permeability quick clay. The pore water pressure displayed a positive linear relation with the snow load, and the ratio of the increase in the pore water pressure to the snow load ( ru snow ) was 0.49–0.53. These values show that approximately half of the snow load contributed to the excess pore water pressure. Continuous field-based monitoring was also conducted for another landslide in relatively high-permeability deposits in Japan, where the pore water pressure showed a relatively low ru snow of about 0.15 and a different timing of the pressure peak. This comparative result indicates that the response characteristics of pore water pressure to the snow loading are strongly affected by the permeability of the landslide mass. Although the excess pore water pressure generated by the snow load theoretically had a negative effect on the slope stability, the value of excess pore water pressure at the monitored landslide was relatively too small to affect its stability. [ABSTRACT FROM AUTHOR]

Studies of the volume change behaviour of saturated and unsaturated fine-grained soils upon exposure to various types of fluid are of significant interest while dealing with contaminated soils. In this study, the one-dimensional volume change behaviour of two clays (Spergau kaolin and Calcigel bentonite) with dominant minerals as kaolinite and montmorillonite was studied by inundating several initially unsaturated and saturated clay specimens with water and a non-polar organic liquid (heptane). For both cases, applied vertical pressures of 25 and 100 kPa were considered under oedometric conditions. The magnitude of compression and swelling deformations of the clays were found to be strongly dependent upon the mineralogy of clays, dielectric properties of the pore-fluid, initial compaction conditions, and applied stress during the wetting process. The test results indicated distinct interactions between unsaturated clays and water. Specimens of Spergau kaolin exhibited compression with water, whereas specimens of Calcigel bentonite exhibited swelling. Compression and swelling deformations of the clays with heptane as the inundating liquid remained within about ±1.0% for both clays indicating a very minor interaction between unsaturated clays and molecules of this non-polar organic liquid. The test results emphasized the significance of attractive and repulsive forces and their impact on the volume change behaviour of clays of different mineralogy. [ABSTRACT FROM AUTHOR]

Liquid manure applied on the soil surface may alter its hydraulic conductivity by surface sealing. In this study, we evaluated the chemical and physical mechanisms of the surface sealing process acting in sandy clay loam and clayey soils after liquid manure application (LDM). Factors affecting surface sealing, such as LDM dosage, total solids content of LDM, straw cover, and time after LDM application, were also studied. The saturated hydraulic conductivity (K sat ) was determined before and 24 h and 7 days after LDM application, and the sealing index was calculated. The liquid dairy manure application on the soil surface promoted surface sealing in both soils; around 93% of sealing surface was due to physical mechanisms and around 7% chemical mechanisms. The application of LDM with 9.4% total solids (TS) promoted a greater sealing index (greater surface sealing) compared to LDM with 0% TS, mainly within 24 h of LDM application. Greater surface sealing was also observed with a higher LDM dose (60 m 3  ha −1 ). Soil cover with 5 Mg ha −1 of straw resulted in a lower sealing index (lower surface sealing) than soil with 0 Mg ha −1 of straw. Sealing index was greatest at 24 h after LDM application for all treatments (solids content, LDM dose and soil cover) in both soils (clayey and sandy clay loam). The clayey soil was more susceptible to surface sealing after LDM application than the sandy clay loam. In practical terms, application of LDM with a high total solids content to bare soil when followed by rainfall 24 h after LDM application, enhanced susceptibility to surface sealing and, consequently, greater detrimental effect on surface water quality. [ABSTRACT FROM AUTHOR]

Biochar amendment can change the soil pore architecture and improve soil physical and hydraulic properties. In this study, two clayey soils were selected and treated with or without biochar amendment (four treatments). Synchrotron-based X-ray micro-computed tomography (SR-mCT) was used to characterize pore structures of the selected aggregates from the treatments. Based on the high-resolution soil pore structure information, the three-dimensional lattice Boltzmann (LB) method was used to simulate water flow in pores. The highresolution soil pore structures were also used to define the internal boundary conditions in the LB method that was accelerated by graphics processing unit parallel computing. Results showed that biochar amendment increased soil permeability by at least one order of magnitude, reduced tortuosity by 20 to 30%, and resulted in more uniformly distributed pore water velocities, which was attributed to the change in soil pore geometry. This study is the first physically based modeling effort to assess the effect of biochar amendment on hydraulic properties of soil aggregates. The SR-mCT method and modeling approach developed in the research play an important role in understanding the mechanisms of water and nutrient transport in soil at the pore scale. [ABSTRACT FROM AUTHOR]

Subsurface drain trenches are important pathways for water movement from the field surface to subsurface drains in low permeability clayey soils. The hydrological effects of trenches installed with well conducting backfill material and gravel inlet patches are difficult to study with only experimental methods. Computational three-dimensional soil water models provide additional tools to assess spatial processes of such drainage system. The objective was to simulate water flow pathways with 3-D FLUSH model in drain spacing and trench depth scale with two model configurations: (1) the total pore space of soil was treated as a single continuous pore system and (2) the total pore space was divided into mobile soil matrix and macropore systems. Both model configurations were parameterized almost solely with field data without calibration. Data on soil hydraulic properties and drain discharge measurements were available from a clayey subsurface drained agricultural field in southern Finland. The effect of soil hydraulic variability on water flow pathways was assessed by generating computational grids in which the hydraulic properties were sampled randomly from five measured soil sets. Both model configurations were suitable to describe the recorded drain discharge, when model was parameterized in finer scale than drain spacing and the parameterization described highly conductive subdomains such as macropores in a dual-permeability model or the trench in a single pore system model. Models produced similar hourly discharge and water balance results with randomly sampled soil hydraulic properties. The results provide a new view on consequences of soil heterogeneity on subsurface drainage. The practical implication of the results from different drainage scenarios is that gravel trench appears to be important only in soils with a poorly conductive subsoil layers without direct macropore connections to subsurface drains. Solely drain discharge data was not sufficient to determine the differences in water flow pathways between the two model configurations and more output variables, such as groundwater level, should be taken into account in making assessments on the effects of different drainage practices on field drainage capacity. [ABSTRACT FROM AUTHOR]

Dispersive clays are prone to erosion and could cause significant problems in geotechnical and geo-environmental projects. In this research, a new additive - the ZELIAC – was investigated for treating a Malaysian dispersive clay soil where an appreciable decrease in dispersivity was achieved due to treatment with 8% ZELIAC. The curing time was found to be significant that after 28 days, the initially dispersive samples became non-dispersive. Furthermore, due to the treatment, the samples had increased unconfined compressive strength (UCS), permeability, and optimum moisture content; and decreased fines content, plasticity index, maximum dry density, and compressibility index. The UCS increased nearly 7.3 times for sample treated with 8% ZELIAC and cured for 90 days. The X-ray fluorescence (XRF) results showed a cementitious structure with calcium content 10.8 times more in the treated sample than in the untreated one, reflecting the constructive cation exchange reaction taking place during the curing process. The sodium ion was noticeably replaced by calcium ion which resulted in a decreased thickness of the diffused double layer and the subsequent reduction in the dispersivity of the sample. These results were also reflected by the lower peak intensity as measured by the X-ray diffraction test (XRD) for the treated sample, as compared to the higher peak intensity for the un-treated sample. Finally, the SEM images indicate that the flocculated structures of the treated dispersive clay were surrounded by the ZELIAC particles. Thus, the ZELIAC was proven to be effective in improving the studied Malaysian dispersive clay. [ABSTRACT FROM AUTHOR]

The variation of stress-strain state induces changes in the permeability of clayey soil and then affects the properties of seepage and consolidation. In previous studies, variations of the permeability of soil in shear process were mainly neglected, and there were no reasonable descriptions of the permeability in such a condition. To study the variation of the hydraulic conductivity of clayey soil in shear process, new triaxial seepage equipment was designed by changing the conventional triaxial apparatus. Based on a series of tests under different confining pressures carried out by this equipment, the influences of the stress-strain state of clayey soil on hydraulic conductivity were investigated. Furthermore, a mathematical model for the hydraulic conductivity of clayey soil under the condition of large shear deformation was proposed. The comparison between the seepage test results and the calculated values of the proposed model indicates that the mathematical model can calibrate the effects of the void ratio and the mesostructure on the hydraulic conductivity of soil in shear process very well. [ABSTRACT FROM AUTHOR]

The effect of irrigation with treated wastewater (TWW) on soil physico-chemical and hydraulic properties was evaluated in this study. Field treatments were: non-irrigated (rain-fed) plot (control), rain-fed plot for the first three years and irrigated with TWW for the last two years (2 yr) and plot irrigated with TWW for five years (5 yr). Soil samples were collected from two depth intervals (0–15 and 15–30 cm) in five replicates. Irrigation with TWW significantly increased aggregate stability (AS), exchangeable sodium percentage (ESP), organic matter (OM), and electrical conductivity (EC). Both hydraulic conductivity (HC) and cumulative infiltration (F(t)) were decreased significantly with TWW use and period of application. Moreover, reduction of HC at different tension revealed that pore clogging occurred at both, macro and micro scale. Scanning electron microscopy (SEM) images showed that soil pores were clogged partially and/or fully as a result of suspended particulates and organic matter. Enhanced AS of treated areas indicated that infiltration was more affected by pore clogging than soil dispersion and swelling. [ABSTRACT FROM AUTHOR]

Conflicting recommendations and opinions can be found in literature concerning the effects of a delayed compaction of lime-stabilized soils. This study was carried out to evaluate such effects on a clayey soil (CH) with 5% of quicklime and hydrated lime. One-dimensional consolidation and hydraulic conductivity tests were carried out on samples compacted soon after lime addition and after 48 h. Analysis of results, helped by scanning electron microscopy and mercury intrusion porosimetry, shows that, for the tested soil, delayed compaction causes a reduction of the dry unit weight up to 11% with hydrated lime and to 18% with quicklime and a greater compressibility of the mixtures at high pressures (at 800 kPa the compression index of samples compacted with delay is doubled relative to that of the immediately compacted ones). However, pozzolanic reaction was found to progress with curing time, even in the case of delayed compaction. The hydraulic conductivity is not significantly modified by a delayed compaction; it is strongly affected by the wetting conditions of curing in the case of hydrated lime. In general, a prompt compaction is always recommendable after addition of hydrated lime whereas the use of quicklime mitigates the influence of a delayed compaction. [ABSTRACT FROM AUTHOR]

Compensation grouting is often employed as a mitigation technique to reduce the settlements induced by tunneling. The efficiency of compensation grouting, defined as the ratio of the volume of heave induced at the ground surface to the volume of injected grout, is strongly dependent on grout properties, injection characteristics, and soil properties. In clayey soils, site observations and laboratory tests show high values of compensation efficiency immediately after injection. However, the efficiency can decrease with time if positive excess pore-water pressures develop in the soil during the injection process. Conversely, in sandy soils, a loss of volume occurs because of pressure filtration of the grout during and soon after the injection process, which reduces the compensation efficiency. This paper describes an analytical model that can be used to evaluate the volume loss produced by pressure filtration of cement-bentonite grouts as a function of soil, grout, and injection parameters. The magnitude of pressure filtration is evaluated as the grout efficiency, which is given by the ratio of the volumes of the final grout body to the injected grout. Results show that the grout efficiency increases with decreasing soil permeability and with increasing grout bentonite content. The result of a grout injection test on a silty soil is back-analyzed using this approach in which the grout efficiency is first evaluated through the proposed filtration model and then used to calibrate a numerical simulation of the test. The good agreement between experimental data and computed results shows that prediction of the efficiency of compensation grouting can be improved using the proposed approach. [ABSTRACT FROM AUTHOR]

Compacted clay liners (CCL) can be used to isolate hazardous wastes like the soil and military scrap contaminated with depleted uranium that emanated from the Iraqi wars in 1991 and 2003. Near-surface repositories for such dangerous waste can preferably be located in the Iraqi deserts, which make up 60% of the territory of Iraq. CCLs are usually constructed using a mixture of clayey soil and coarse material compacted in air-dry form or suitably wetted. In the present study, two smectitic soils from Iraq, termed green and red clays, were investigated for potential use in CCLs. The shear strength, swelling pressure, hydraulic conductivity and creep properties were determined and used for preliminary design of top and bottom-liners. The engineering properties were determined for various dry densities and water contents ranging from air-dry to fully saturated conditions. The results showed that mixtures of sand and 30%–50% green clay and mixtures of sand and 40%–60% red clay are suitable for constructing top-liners with a hydraulic conductivity between 1 × 10 − 10 and 1 × 10 − 9 m/s. For bottom-liners, mixtures of sand and 70% green clay and mixtures of sand and 80% red clay can be considered. They were found to have a hydraulic conductivity of 1 × 10 − 11 m/s for a density at saturation of 2.1 g/cm 3 (dry density, 1.7 g/cm 3 ). As to the slope stability of top-liners, the shear strength for different clay percentages was found to guarantee slope stability for 18° inclination under both air-dry and water saturated conditions. [ABSTRACT FROM AUTHOR]

• A theoretical expression of P EDL as a function of SAR and EC was derived. • Effects of SAR and EC on surface potential of soil particle were quantified. • Changes of theoretical P EDL with SAR and EC agree with measured K s values. • Infiltration rate can be arbitrarily adjusted by P EDL for a given soil. Sodium adsorption ratio (SAR) and electrolyte concentration (EC) can significantly affect water movement in soil. However, the theoretical mechanisms behind it are rarely studied. In the present study, an analytical function between electrostatic repulsive pressure (P EDL) and SAR/EC was derived in Na-Ca mixed electrolyte solutions or soil water. Soil water SAR and EC controls P EDL through surface potential and midpoint potential between two adjacent soil particles, which consequently influences the saturated soil hydraulic conductivity (K s). Theoretical calculations show that the P EDL decreases with increasing EC and increases with increasing SAR, and the reduction in K s is correlated with the repulsive P EDL. Five soils of different dominant clay minerals, specifically kaolinite (K), illite (I) and montmorillonite (M), were used to investigate the relationship between P EDL and change of K s. The soils were packed in columns and leached with a serial of solutions (constant EC values of 0.5, 1, and 2 ds m−1, respectively) with increasing SAR from 0 to infinity. Our study showed that the K s decreases with increasing P EDL. At the inflection point of the percent of K s reduction (K red) vs. P EDL curve, the critical P EDL values are 8.358 ∼ 8.569 atm and K red > 92% for the Mungana soil (M), Yarrandoo soil (M, K) and Dunholm soil (M), while the average critical P EDL value is about 12.34 atm and K red is only ∼51.75% for the Urrbrae soil (I) and Timberlea soil (K). For a given soil, the P EDL is the determinant factor, while other factors such as soil texture and clay type can also affect K s. [ABSTRACT FROM AUTHOR]

A review of the McNeal clay swelling model, including its underpinning assumptions and the method for determining its parameters, was undertaken. Limitations of the model include model parameter identification, the fixed threshold exchangeable sodium percentage level at which hydraulic conductivity begins to decline, and the assumption that the expanding clay will always be 10% of the soil. To overcome these problems, an improved form of the model that accommodates a range of clay content is proposed. The modified model was used to estimate the reduction in saturated hydraulic conductivity in the three McNeal groups of soils containing different percentages of expanding clay. The model produced good agreement between the observed and estimated saturated hydraulic conductivities over the entire range of irrigation salinity (3-200 mmolc/L) and sodicity used for the original swelling model. The modified model was also successfully validated against three new sets of relative hydraulic conductivity data. The generalization of interlayer clay swelling in the modified model is more appropriately described as determining the dispersive potential of a given solution, rather than physical interlayer swelling. Consequently, this modified model more accurately predicts the reduction in saturated hydraulic conductivity as a function of the sodicity and salinity of the applied water. [ABSTRACT FROM AUTHOR]

Some important engineering characteristics of compacted clay liners can be adversely affected by desiccation cracking, resulting in the loss of effectiveness and integrity of containment systems as a barrier. Recently, there has been interest in using tire chips as an additive material to prevent desiccation cracking. In this study, compaction, shrinkage, and desiccation cracking tests were performed to study the effect of tire chips on suppressing shrinkage and desiccation cracks in clayey soils. The percentages of tire chips used were 10%, 20%, and 30% by weight. The results of shrinkage tests indicate that the percentage of volume change of the specimens decreases with addition of tire chips and its value also is affected by size of the tire chips. The intensity of cracks diminishes in the clay-tire mixtures so that the observed crack reduction in the range of used tire chips content is about 40% to 80%. The optimum tire chips content also is necessary to achieve maximum crack reduction and minimum shrinkage strain, while maintaining acceptable hydraulic conductivity. This study suggests the potential application of waste tires to suppress desiccation cracks encountered in landfill clay liners. [ABSTRACT FROM AUTHOR]

A large amount of coal fly ash produced in thermal power plants is disposed of in landfills which causes many environmental problems. The utilization of fly ash can be encouraged in geotechnical engineering projects. In this paper, the effects of class C and class F fly ash on the mechanical and microstructural behavior and stabilization of clay soil were evaluated through a program of laboratory experiments. The experiments included compaction, unconfined compressive strength, consolidated-undrained triaxial, one-dimensional consolidation tests, and scanning electron microscopy analysis on samples of fly ash-stabilized clay soil after 1, 7, and 28 days of curing. The tests were conducted on mixtures of clay with class C or class F fly ash, ranging from 0% to 30% of the soil. Experimental results showed that the strength parameters and permeability of the stabilized soil improved while the compression and swelling indices decreased by the addition of fly ash and by the increase of curing days. The results obtained from the mechanical tests agreed with the results from the SEM analysis. Based on the results, the soil could be successfully stabilized by using class C fly ash. The improvements in strength, swelling, and permeability parameters of the stabilized soil were higher with the class C fly ash compared with class F fly ash. [ABSTRACT FROM AUTHOR]

Applying soil amendments plays a critical role in relieving water stress in arid and semiarid areas. The natural clay mineral attapulgite (ATP) can be utilized to adjust the balance of water and soil environment. In this study, we investigated four different particle size distribution typical soils in the Loess Plateau: (1) lou soil (LS), (2) dark loessial soil (DS), (3) cultivated loess soil (CS), (4) sandy soil (SS). Five ATP application rates (0, 1%, 2%, 3%, and 4%) were selected to test the effect of ATP on the soil water retention curve, soil saturated hydraulic conductivity, and soil structure. The results showed that applied ATP significantly increased the soil clay content, and the relative change of SS with 3% ATP applied increased by 53.7%. The field water holding capacity of LS, DS, CS, and SS with 3% ATP applied increased by 8.9%, 9.6%, 18.2%, and 45.0%, respectively. Although applied ATP reduced the saturated hydraulic conductivity, the values of CS and SS were opposite when the amount of ATP applied was >3%. The relative change in the amount of 0.25–1 mm soil water-stable aggregates of SS was 155.9% when 3% ATP was applied. Applied ATP can enhance soil water retention and soil stability, which may improve limited water use efficiency and relieve soil desiccation in arid and semiarid areas or similar hydrogeological areas. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Summary: Occurrence of temporal stability of soil water content has been observed for a range of soil and landscape conditions and is generally explained as a consequence of local and non-local controls. However, the underlying factors for this phenomenon are not completely understood and have not been quantified. This work attempts to elucidate and quantify the effects of several local controls, such as soil hydraulic properties and root water uptake, through water flow simulations. One-dimensional water flow was simulated with the HYDRUS code for bare and grassed sandy loam, loam and clay soils at different levels of variability in the saturated hydraulic conductivity Ksat . Soil water content at 0.05 and 0.60m and the average water content of the top 1m were analyzed. Temporal stability was characterized by calculating the mean relative differences of soil water content in 100 soil columns used for each combination of soil and season. Using log-normal distributions of Ksat resulted in mean relative differences distributions that were commonly observed in experimental studies of soil water content variability. Linear relationships were observed between scaling factor of ln Ksat and spread of the mean relative differences distributions. For the same scaling factor and soil texture, simulated shapes of the mean relative differences distributions depended on the duration of the simulation period and the season. Variation in mean relative differences was higher in coarser textures than in finer ones and more variability was seen in the topsoil than in the subsoil. Root water uptake decreased the mean relative differences variability in the root zone and increased variability below it. This work presents a preliminary research to promote the use of water flow simulations under site-specific conditions to better understand the temporal stability of soil water contents. The estimation of the spatial variability of Ksat from soil water content monitoring presents an interesting avenue for further research. [Copyright &y& Elsevier]

Abstract: The soil hydraulic conductivity (K) is an important parameter for understanding soil hydrologic processes. K varies with time, soil type, and irrigation method. Understanding and predicting the temporal variability of K are required for irrigation design and numerical analyses. The objective of this study was to investigate and evaluate the temporal variability in K from April to September of 2008 in two soils, clay loam (CLS) and sandy loam (SLS), and two irrigation methods, furrow irrigation (FIM) and drip irrigation (DIM). Five sets of infiltration measurements with five replications were taken in grape fields using a tension infiltrometer at supply h values of −15, −6, −3, and 0cm. The results showed that K had significant temporal differences under all supply h values. Generally, K initially exhibited high values and decreased from April to September. K of SLS was always significantly higher than that of CLS. K values were lower and varied more for FIM than for DIM, but showed no statistically significant difference between the two irrigation methods. About 1.3 to 2.9 times differences existed between the maximum mean K (in April) and minimum mean K values (in July/September) through the whole growing period. However, the relative errors between the calculated K and measured K diminished within 10% when K was estimated using a regression to adjust K to the number of irrigation events. These results contribute to a more accurate description of K for irrigation design and water flow modeling. [Copyright &y& Elsevier]

Infiltration of water in unsaturated soils has long been an interest of study in geotechnical engineering. A wide range in permeability coefficient has been proven to be a major obstacle in analyzing seepage problems. Soil-water characteristic curve (SWCC) is a fundamental constitutive relation for the explanation of the engineering behaviour of unsaturated soil. The effect of anisotropy on SWCC and unsaturated coefficients of permeability and diffusion has been studied in this paper, by taking sets of duplicate disturbed and undisturbed specimens prepared in the vertical, 45° inclined and horizontal directions. The results showed that there is a noticeably anisotropic in the basic characteristics of SWCC and the unsaturated coefficients of permeability and diffusion specially at the low values of suction. The variations of the hydraulic conductivity and vapor diffusivity versus suction gradient were opposite. Furthermore there is a noticeable difference between the disturbed and undisturbed specimens in the SWCC and coefficients of diffusion and permeability. [ABSTRACT FROM AUTHOR]

Summary: Water flow is a key component in the evaluation of soil erosion and nutrient loads from agricultural fields. Field cultivation is the main non-point pollution source threatening water quality of surface waters in Nordic and many other countries. Few models exist that can describe key hydrological processes in clayey soils, i.e. overland flow, preferential flow in macropores and soil shrinkage and swelling. A new three-dimensional (3-D) distributed numerical model called FLUSH is introduced in this study to simulate these processes. FLUSH describes overland flow with the diffuse wave simplification of the Saint Venant equations and subsurface flow with a dual-permeability approach using the Richards equation in both macropore and matrix pore systems. A method based on the pentadiagonal matrix algorithm solves flow in both macropore and matrix systems directly in a column of cells in the computational grid. Flow between the columns is solved with iteration accelerated with OpenMP parallelisation. The model validity is tested with data from a 3-D analytical model and a clayey subsurface drained agricultural field in southern Finland. According to the simulation results, over 99% of the drainflow originated from the macropore system and drainflow started in some cases within the same hour when precipitation started indicating preferential flow in the profile. The moisture content of the clay soil had a profound effect on runoff distribution between surface runoff and drainflow. In summer, when the soil was dry and cracked, drainflow dominated the total runoff, while in autumn, when the shrinkage crack network had swollen shut, surface runoff fraction clearly increased. Observed differences in surface runoff fraction before and after tillage indicated that the operation decreased hydraulic conductivity of the profile. [ABSTRACT FROM AUTHOR]

Abstract: Three natural clayey soils from Tunisia were studied to assess their suitability for use as a liner for an acid waste disposal site. An investigation of the effect of the mineral composition and mechanical compaction on the hydraulic conductivity and fluoride and phosphate removal of three different soils is presented. The hydraulic conductivity of these three natural soils are 8.5×10−10, 2.08×10−9 and 6.8×10−10 m/s for soil-1, soil-2 and soil-3, respectively. Soil specimens were compacted under various compaction strains in order to obtain three wet densities (1850, 1950 and 2050kg/m3). In this condition, the hydraulic conductivity (k) was reduced with increasing density of sample for all soils. The test results of hydraulic conductivity at long-term (>200days) using acidic waste solution (pH=2.7, charged with fluoride and phosphate ions) shows a decrease in k with time only for natural soil-1 and soil-2. However, the specimens of soil-2 compressed to the two highest densities (1950 and 2050kg/m3) are cracked after 60 and 20days, respectively, of hydraulic conductivity testing. This damage is the result of a continued increase in the internal stress due to the swelling and to the effect of aggressive wastewater. The analysis of anions shows that the retention of fluoride is higher compared to phosphate and soil-1 has the highest sorption capacity. [Copyright &y& Elsevier]