Search

Soil hydrology seriously affects the prevention of desertification in karst areas. However, water infiltration in the different soil layers of secondary forests and artificial forests in karst areas remains uncertain. This lack of clarity is also the factor that constrains local vegetation restoration. Therefore, monitoring and simulating the priority transport of soil moisture will help us understand the shallow soil moisture transport patterns after artificial vegetation restoration in the local area, providing a reference for more scientific restoration of the ecological environment and enhancement of carbon storage in karst areas. The integration of soil physical property assessments, computed tomography (CT) scanning, dye tracing studies, and HYDRUS-2D modeling was utilized to evaluate and contrast the attributes of soil macropores and the phenomenon of preferential flow across various forestland categories. This approach allowed for a comprehensive analysis of how the soil structure and water movement are influenced by different forest ecosystems and infiltration head simulations (5 mm, 15 mm, 35 mm, and 55 mm) to elucidate the dynamics of water movement across diverse soil types within karst regions, to identify the causes of water leakage due to preferential flow in secondary forests, and to understand the mechanisms of water conservation and reduction in artificial forests adopting a multifaceted approach. This study demonstrated that (1) the soil hydrological capacity of a plantation forest was 20% higher than a natural forest, which may be promoted by the clay content and distribution. (2) Afforestation-enhanced soils in karst regions demonstrate a significant capacity to mitigate the loss of clay particles during episodes of preferential flow and then improve the soil erosion resistance by about 5 times, which can effectively control desertification in karst area. (3) The uniform distribution of macropores in plantation forest soil was conducive to prevent water leakage more effectively than the secondary forest but was incapable of hindering the occurrence of preferential flow. The secondary forest had a very developed preferential flow phenomenon, and soil clay deposition occurred with an increase in depth. (4) Moreover, the results for preferential flow showed that the matrix flow depth did not increase with the increase in water quantity. Short-term and high-intensity heavy rainfall events facilitated the occurrence of preferential flow. Infiltration along the horizontal and vertical directions occurred simultaneously. These results could facilitate a further understanding of the contribution of the plantation to soil amelioration and the prevention of desertification in karst areas, and provide some suggestions for the sustainable development of forestry in karst areas where plantation restoration is an important ingredient. [ABSTRACT FROM AUTHOR]

Soft clay is identified to have some unfavorable characteristics when used as the foundation for construction work. This is due to the low bearing capacity and high compressibility which often leads to prolonged consolidation settlement. Therefore, soil improvement is necessary, and this can be achieved through the Vacuum Consolidation Method (VCM). This research focused on conducting laboratory-scale model tests to determine the characteristics of clay soil improved by vacuum consolidation in terms of its physical properties, hydrolysis, and compressibility. The results showed that the water content decreased as soil approached the Prefabricated Vertical Drain (PVD). A similar trend was also observed for the compression index value; this is because local density occurs in the soil near the PVD as a result of the movement of fine particles towards the PVD, which fills the empty pore space. Moreover, soil permeability in both vertical and horizontal directions reduced, and the soil became anisotropic after VCM improvement. The results of this research can be a consideration in the use of the VCM method for soft soil improvement, especially the problem of clogging zones that occur due to the suction pressure of the vacuum pump, which can reduce the performance of the VCM. [ABSTRACT FROM AUTHOR]

Obtaining accurate values of saturated hydraulic conductivity (Ksat) is very important for managing all natural or artificial processes involving water flow into soils. Double-ring infiltration (DRI) is one of the easiest-to-work-with techniques commonly used for Ksat determination. Unfortunately, when improperly used, it leads to important variations and inaccurate results. This study was designed to investigate the necessary conditions to reach the true-value or real-world saturated hydraulic conductivity (Ksat-real-world) in the field. For this purpose, the effects of two factors—namely, the measured infiltration data type (cumulative, instant rate, and average rate) and the related non-linear regression equation type—were analyzed. Measurements with DRI were performed with samples from 106 locations in three West African countries, namely, Burkina Faso, Mali, and Cote d'Ivoire. The soils were composed of loam, sandy loam, and sandy clay loam. The results show that when infiltration rates are used rather than cumulative infiltration non-linear regression curves, the variability between the measured Ksat and the real-world saturated hydraulic conductivity (Ksat-real-world) could reach from 2.2% to 58.8%. This variability was caused by the approximate amplification—according to the procedure used—of time-increment measurement errors. Extending the test duration to more than 4 h, especially when clay soils were involved, and using the exponential one-phase decay non-linear regression of the cumulative infiltration data based on a clear measurement protocol provided the Ksat values that were closest to Ksat-real-world. [ABSTRACT FROM AUTHOR]

Clay is a soil with low permeability. Clay is considered a problematic soil besides peat soil. The main problem with clay is its mineralogy. Expansive clay soils contain the minerals kaolinite, illite, and montmorillonite. Montmorillonite has weak bonds between its layers. These weak bonds make the soil easily incorporated, one of which is water. Water approaching expansive soil will bond with it and cause swelling. Expansive soil improvement studies have been conducted. One of them is electrokinetic. Expansive soil from Karawang, Indonesia is one of the soils with a high swelling index. This is because montmorillonite is inside. The Karawang expansive soil will be improved by flowing several salt solutions with various voltages. The applied voltage will flow the solution from the anode to the cathode and fill the clay minerals. Four voltage variants will be applied with the same electrokinetic application time. The mineralogy of soil before and after electrokinetic improvement undergone changes. The changes can be seen from SEM and XRF testing. The improved soil changed its physical properties from clay with high plasticity to clay with low plasticity. Chemical elements from salt solution trap in montmorillonite then make positive changes in soil mineralogy, soil physical properties, and mechanical properties. The mechanical properties can be seen in a decrease in the C value and an increase in the soil angle of friction after electrokinetic improvement. After electrokinetic improvement using calcium chloride, the lowest soil cohesion value was 12.356 kg/cm² at 12 V. After electrokinetic improvement with calcium dioxide, the lowest cohesion value at 12 V voltage is 19.22 kg/cm². In barium sulfate solution, the lowest soil cohesion at 15 V is 12.16 kg/cm². The soil swelling value decreased after improvement with calcium chloride to 0.008 % from 0.027 %. The research results in calcium chloride with 12 V give optimized results on soil improvement with electrokinetics [ABSTRACT FROM AUTHOR]

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 present work determined the influence of superhydrophobic nano-SiO2 on the hydraulic conductivity and pore size distribution of expansive soil, and analysed the mechanism of modification between superhydrophobic nano-SiO2 and expansive soil from a microscopic view. Superhydrophobic nano-SiO2 was added to expansive soil as a modifier. Our samples were of two types, i.e., unmodified (without nano-SiO2) and modified (with 0.2%, 0.4%, 0.6%, 0.8%, and 1.0% nano-SiO2 by weight of the parent soil). The hydraulic conductivity decreased with increasing nano-SiO2 content. Fourier transform mid-infrared test revealed that some silanols in soil and nano-SiO2 were dehydrated and condensed to form siloxanes. We inferred that nano-SiO2 can attach onto the surface of soil particles to form a hydrophobic membrane, which reduced the soil expansion and the change in pore size distribution. And microscopic tests showed that the pore volume and hydrophilicity of the soil samples decreased with increasing SiO2 content. According to the Young–Laplace equation, the minimum permeable pore radius was calculated in the hydraulic-conductivity test. With increasing nano-SiO2 content, the volume of permeable pore decreased. It had an excellent linear relationship with the hydraulic conductivity and permeable pore volume of samples containing different nano-SiO2 contents. Therefore, superhydrophobic nano-SiO2 could effectively reduce hydraulic conductivity by changing the pore size distribution of expansive soil. [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]

Advances in additive manufacturing create unique opportunities for the investigation of permeability of fine-grained soils. The permeability of fine-grained soils, such as clays, plays an important role in various design considerations in the geotechnical, environmental, and stormwater management systems. This research investigates the application of 3D printed specimens in studying the hydraulic and mechanical properties of clayey soils. The effects of 3D printing, specifically direct binder jet printing, on the permeability, and other physical properties of clay were investigated. Cylindrical clay specimens were prepared using an advanced direct binder jet printing and tested in a flexible wall permeameter and triaxial compression setup under effective confining stresses representing clay at very shallow depths. The results of this study show that the 3D printing process affects the permeability of clay through changes in physical properties such as the specific surface area. However, the printing provides consistent and repeatable specimens with very low disturbance and efficient controlled geometry. Also, due to stiffer 3D printed specimen, less confinement impact was observed in 3D printed specimens. Also, 3D printed specimens showed significantly higher shear strength and friction angle. The outcome of this research could pave the path for future studies dealing with flow through fractured clays. Article Highlights: 3D printing and sintering change the physical properties of clay powder leading to higher permeability. The impact of confining pressure on 3D printed specimens is considerably low. 3D printing increases the shear strength of soil specimens. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Agro-Environment Science is the property of Journal of Agro-Environment Science Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

Recycled waste materials have been employed to stabilize clayey soil by many practitioners in geotechnical engineering. However, the effects on hydraulic conductivity and its underlying mechanism have rarely been explored. The study aims to examine the hydraulic conductivity characteristics of soil reinforced with the inclusion of selected recycled waste granules, rubber crumb (RC) and crushed glass (CG) under changing confinement. For this purpose, a series of consolidation tests were carried out by varying recycled waste type and additive contents (0%, 5%, 10% and 20% additive content by dry weight of soil). The confining stress was increased within a range of 6.25 kPa to 200 kPa. The results reveal that the addition of RC and CG, as well as the stress state, significantly impacted the soil's hydraulic conductivity (k). The hydraulic conductivity of both RC/CG soil composites consistently declined with increasing applied stress. Moreover, as the concentration of recycled waste granules in the reinforced soil increased, the hydraulic conductivity value k initially increased, reaching a peak before subsequently declining. Additionally, the study utilized scanning electron microscope (SEM) imaging, which revealed that the inclusion of RC and CG significantly influenced hydraulic conductivity-related parameters by modifying pore size and distribution. [ABSTRACT FROM AUTHOR]

Malaria is a permanent threat to health in western Burkina Faso. Research has shown that geographical variables contribute to the spatial distribution in its transmission. The objective of this study is to assess the relationship between malaria prevalence and potential explanatory geographical variables in the Houet province in Burkina Faso. Statistics on malaria prevalence registered by health centres in the Houet province in 2017 and potential geographical variables identified through a literature review were collected. An Ordinary Least Squares (OLS) regression was used to identify key geographical variables and to measure their association with malaria while the Getis Ord Gi* index was used to locate malaria hotspots. The results showed that average annual temperature, vegetation density, percentage of clay in the soil, total annual rainfall and distance to the nearest waterbody are the main variables associated with malaria prevalence. These variables account for two-thirds of the spatial variability of malaria prevalence observed in Houet province. The intensity and direction of the relationship between malaria prevalence and geographical factors vary according to the variable. Hence, only vegetation density is positively correlated with malaria prevalence. Average temperature, for soil clay content, annual rainfall and for distance to the nearest water body are negatively correlated with the disease prevalence. These results show that even in an endemic area, malaria prevalence has significant spatial variation. The results could contribute to the choice of intervention sites, as this choice is crucial for reducing the malaria burden. [ABSTRACT FROM AUTHOR]

The direct estimation of soil hydraulic conductivity (Ks) requires expensive laboratory measurement to present adequately soil properties in an area of interest. Moreover, the estimation process is labor and time-intensive due to the difficulties of collecting the soil samples from the field. Hence, innovative methods, such as machine learning techniques, can be an alternative to estimate Ks. This might facilitate agricultural water and nutrient management which has an impact on food and water security. In this spirit, the study presents neural-network-based models (artificial neural network (ANN), deep learning (DL)), tree-based (decision tree (DT), and random forest (RF)) to estimate Ks using eight combinations of soil data under calcareous alluvial soils in a semi-arid region. The combinations consisted of soil data such as clay, silt, sand, porosity, effective porosity, field capacity, permanent wilting point, bulk density, and organic carbon contents. The results compared with the well-established model showed that all the models had satisfactory results for the estimation of Ks, where ANN7 with soil inputs of sand, silt, clay, permanent wilting point, field capacity, and bulk density values showed the best performance with mean absolute error (MAE) of 2.401 mm h−1, root means square error (RMSE) of 3.096 mm h−1, coefficient of determination (R2) of 0.940, and correlation coefficient (CC) of 0.970. Therefore, the ANN could be suggested among the neural-network-based models. Otherwise, RF could also be used for the estimation of Ks among the tree-based models. [ABSTRACT FROM AUTHOR]

Bentonite clay is most commonly used as a landfill liner but is resource-intensive and suffers drawbacks like large volume change and desiccation cracking. It also poses construction difficulties and the handling of a large volume of material. In situ soil can be successfully modified into base liners for landfills which offers an economical and sustainable alternative to bentonite liners. In this study, an exocellular biopolymer, xanthan gum, is used to improve the in situ soil and provides a novel alternative liner material. A comparative study is also made by modifying the in situ soil with various percentage of bentonite. The results show that the maximum dry density of the in situ soil increased marginally for both the additives. Hydraulic conductivity decreased from 2.87 × 10–3 to 4.46 × 10–8 cm/s at 1% xanthan gum addition while in case of bentonite it reduces to 4.81 × 10–8 cm/s at 30% addition. This significant reduction in hydraulic conductivity on stabilizing soil with xanthan gum is attributed to gel coating on the soil surface and gel plug formation in the soil matrix, confirmed by morphological studies. Choice of xanthan gum for stabilizing soil and modifying it into baseliners is economical than bentonite clay. The mechanism of bio-plugging in xanthan gum stabilized soil will also control leachate movement through the soil. Hence, xanthan gum, a renewable, sustainable and carbon negative biopolymer, can be successfully used to modify in situ soil into clay liner. [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]

In this paper, an attempt has been made to investigate the impacts of leaching on the geotechnical and microstructural properties of clayey gypseous soils at various percentages of gypsum; 20 %, 40 %, and 60 %, and their respective densities. In this respect, the work delves into the interaction of the properties based on the following experiments: oedometer permeability leaching and modified permeability leaching tests for investigating the effects of gypsum content, density, and leachate on significant soil properties such as compressibility, permeability, and Total dissolved solids (TDS). Scanning electron microscopy (SEM) and Energy dispersive spectroscopy (EDS) used for microstructural analysis reveal how the soil fabric and dissolution patterns change during leaching. The conclusions derived from the results of the study state that with an increase in the content of gypsum in soil, it increases the porosity and permeability of the soil and at the same time decreases the plasticity. The soils which were denser showed lesser leaching strain due to reduced permeability. It can be ascertained that the modified leaching test is a more realistic and accurate method in comparison to the oedometer test. Results from microstructural observations hence bring out important changes in the soil fabric after leaching: increases in voids and cavities responsible for the change of soil stability and engineering properties. This research allows a good contribution to understanding and the management of gypseous soil behavior in geotechnical engineering projects and provides new lines of future investigation for the long-term performance and stabilization technique of effectiveness. [ABSTRACT FROM AUTHOR]

Soils with low permeability are widely used in solid waste landfills to prevent leakage of leachate into groundwater. By adding nanomaterials to clay soils, the permeability of the clay can be reduced as well as the retention of pollutants in the leachate. In this study, three different nanomaterials, iron oxide, aluminum oxide, and Oltu clay, were added to kaolin at two different rates (1% and 5%), and the effect of nanomaterials on permeability and heavy metal (iron, manganese, zinc, copper, and lead) removal rate was investigated. According to the experimental results, permeability decreased, and the heavy metal removal rate increased with increasing nanomaterial content in kaolin. With the addition of 5% iron oxide, 5% aluminum oxide, and 5% Oltu clay to kaolin, the average permeability decreased by 63%, 81%, and 96%, respectively. Iron (90–93%), manganese (47–75%), zinc (39–50%), copper (33–41%), and lead (36–49%) removal rates of nanomaterial-added kaolin samples were found to be higher than the removal rates of kaolin without nanomaterial addition. Oltu clay, which has the smallest size and high surface area, performed better than aluminum oxide and iron oxide in reducing the permeability of kaolin and retaining heavy metals. [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]

BACKGROUND AND OBJECTIVES: In landfills, containment is provided by natural or artificial clayey materials known for their low permeability and for their pollutant retention capacity. However, the properties of these media are modified by leachates, whose migration they are supposed to limit. This study aims to reconsider the criteria for choosing suitable materials to make a bottom liner through both their long term hydraulic and mechanical performances. METHODS: Two fine materials sampled in Burkina Faso (West Africa) have been characterized in order to compare their hydro-mechanical behavior in the presence of household waste leachates. The first material is classified as an inorganic clay of low to medium plasticity according to Casagrande plasticity diagram, it is mainly kaolinitic with some traces amounts of smectites. The second one is classified clayey sand of low to medium plasticity, the predominant mineral clay being kaolinite. Hydro-mechanical tests were performed on both sampled materials to judge the sealing properties of these materials, as well as the characteristics of deformation and rupture which have an important effect to ensure the durability of a bottom liner. All these tests were performed first with distilled water then with leachates as interstitial fluids in order to understand the modification of the hydro-mechanical properties of the clayey soils. FINDINGS: Leachate contamination always alters hydraulic properties of the materials. However, between the two soils, the most clayey and the most impervious (soils from Nouna) undergo the deeper weathering. Indeed, hydraulic conductivity of these soils in contact with a synthetic leachate increases from 1.71x10-10 to 1.51x10-9 m/s. In contrast to soils from Boudry, these soils also undergo very significant settlements over the long term with compressibility indexes varying from 0.164 to 0.225. For both soils, the shear strength increases showing that, from this point view, the leachate work in the sense of of the bottom liner stability. For soils from Nouna, the effective cohesion increases from 3 to 21 kPa with a slight decrease of friction angle; for soils from Boudry a slight increase of cohesion is noticed while friction angle increases from 34 to 37°. CONCLUSION: This comparative study is of practical use to environmental geotechnics professionals because it shows that the choice in designing a bottom liner must be a compromise between long term hydraulic and mechanical behaviors of soils. It is also important to know the nature of the flows to contain in order to ensure the durability of the structure. [ABSTRACT FROM AUTHOR]

Oxidant injection technology is widely used in soil remediation; however, subsurface conditions, including soil properties and permeability, significantly influence its effectiveness. In this study, the potential of the combination of pneumatic fracturing, plasma discharge, and vacuum extraction (PPV) in enhancing soil permeability and remediating field-scale silt/clayey soils contaminated by total petroleum hydrocarbon (TPH) was studied. Improved soil permeability was assessed by measuring the chlorine and H 2 O 2 concentrations in soil samples, and the remediation efficiency of PPV was evaluated by analyzing the TPH concentrations in the soil samples. The initial highest TPH concentration was 6922 mg kg−1; after a 42-day operation period, the TPH levels decreased to 541 mg kg−1. The economic assessment of PPV revealed it to be cost-effective, with a total operating cost of US$ 3077 for remediating 265 m³ of contaminated soil, equating to US$ 11.6 per ton of soil. Since PPV requires a short operational period, is inexpensive, and is suitable for purifying low-permeability soil, it is a promising and economically advantageous approach for soil purification. Overall, PPV demonstrated the ability to enhance oxidizing agent transfer by increasing soil permeability, suggesting its potential for efficient and targeted soil remediation. [Display omitted] • Combination of pneumatic fracturing, plasma discharge, and vacuum extraction (PPV) was developed. • PPV achieved a purification efficiency of 93.6 % for TPH-polluted clayey soils during 42 days. • PPV exhibits an 8.5-fold increase in H 2 O 2 injection capacity than conventional injection methods. • PPV demonstrated cost-effectiveness, with an operating cost of $11.6 per ton. • PPV method efficiently introduces purifying agents into low permeable silt/clay layers. [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]

When filling embankment dams in cold regions, engineers must solve two freeze—thaw cycle (FTC)-induced soil problems. First, compacted soil constituting the dam is subjected to the FTC during dam construction. Second, loose soil material (LSM), which is subjected to the FTC, fills the dam. To investigate the effects of the aforementioned two problems on the hydraulic conductivity of compacted clayey soil, a series of permeation tests on clayey soil compacted before and after FTC were conducted in this study. The results showed that for the first problem, the hydraulic conductivity of compacted clayey soil subjected to one FTC significantly increases by two to three orders of magnitude because FTC-induced cracks can cause preferential flow in the permeation process. For the second problem, when the FTC number is less than a critical number, the FTC of the LSM may result in the development of united soil particles, thereby increasing the effective porosity ratio and hydraulic conductivity of the compacted soil. It was discovered that the hydraulic conductivity of compacted soil can increase by one to three times when the LSM is subjected to 10 FTCs. When the FTC number exceeds a critical number, the effective porosity ratio and hydraulic conductivity of the compacted soil may decrease with the FTC of the LSM. This should be investigated in future studies, and the results can be used to improve engineering management processes when filling embankment dams during winter in cold regions. [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]

Purpose: Organic amendment applications have been proposed as important agricultural management practices for the maintenance of soil health. Weathered coal (WC), biochar (BC), and grass peat (GP) have been used widely and globally for a long time. However, the differences in soil physical properties following the application of these amendments have rarely been evaluated under the same field conditions. Methods: In this study, the changes in the physical properties of loamy clay soil after applying WC, BC, and GP (3%, w:w) were investigated under field conditions after 375 days. Results: Relative to unamended soil, the WC, BC, and GP applications increased the total porosity and decreased the bulk density of amended soils (P < 0.05). The soil water content increased by 23.8% following the BC application, whereas it was decreased by 10.5% following the GP application (P < 0.05). The application of all the amendments increased the soil average temperature by 0.71 °C (GP), 0.41 °C (WC), and 0.18 °C (BC) (P < 0.05). Additionally, the WC application increased the fraction of aggregates of 1–2 mm in size (by 47.6%) and of 2–5 mm in size (by 65.8%), and the stability of soil aggregates (P < 0.05). All the amendments increased the soil pores (> 300 and 30–300 µm) of amended soils, but the saturated hydraulic conductivity of these soils was not significantly improved. Conclusion: The application of WC can improve the formation and stability of soil aggregates to reduce the risk of soil erosion. BC is suitable for use in drought-prone areas with low rainfall and strong evaporation because it can increase the retention capacity of soil water. GP should be applied with caution, considering that its decomposition after extraction leads to the severe loss of organic carbon to the atmosphere. Overall, the selection of organic amendments in agricultural management practices should take into account the local environmental conditions. [ABSTRACT FROM AUTHOR]

Impermeable base layers that are made of materials with low permeability, such as clay soil, are necessary to prevent leachate in landfills from harming the environment. However, over time, the permeability of the clay soil changes. Therefore, to reduce and minimize the risk, the permeability-related characteristics of the base layers must be improved. Thus, this study aims to serve this purpose by experimentally investigating the effects of nanomaterial addition (aluminum oxide, iron oxide) into kaolin samples. The obtained samples are prepared by applying standard compaction, and the permeability of the soil sample is experimentally investigated by passing leachate from the reactors, in which these samples are placed. Therefore, Flow Resistance (FR) analysis is conducted and the obtained results show that the Al additives are more successful than the Fe additive in reducing leachate permeability. Besides, the concentration values of some polluting parameters (Chemical Oxygen Demand (COD), Total Kjeldahl Nitrogen (TKN), and Total Phosphorus (TP)) at the inlet and outlet of the reactors are analyzed. Three different models (Artificial Neural Networks (ANN), Multiple Linear Regression (MLR), Support Vector Machine (SVM)) are applied to the data obtained from the experimental study. The results have shown that polluting parameters produce high FR regression similarity rates (>75%), TKN, TP, and COD features are highly correlated with the FR value (>60%) and the most successful method is found to be the SVM model. [ABSTRACT FROM AUTHOR]

The clay soil in the middle and lower reaches of the Yangtze River in China is widely distributed and the groundwater table is shallow. In order to accurately analyze the distribution and assess the potentially harmful effects of the pollutants in this region, it's necessary to study the diffusion rate and subsequent concentrations of organic pollutants. Our study area, located in Kunshan in the Jiangsu Province, represents a typical contaminated site consisting of a silty clay layer located in a shallow water table. Our model for the horizontal diffusion, vertical diffusion, and concentration distribution of organic pollutants through this clay layer over 30 years. The simulation results were compared to the measured horizontal distribution of the pollutant concentration at a depth of 2 m and the electrical resistivity tomography data reflecting the longitudinal changes in the polluted area. Our model generated accurate pollutant concentration and diffusion depth results, but the modelled horizontal diffusion distance of the pollution plume did not agree with observational data. After increasing the soil permeability coefficient at a depth of 2 m by a factor of 20,000, the numerical simulation results more closely match those of the measured results. Based on model results, we propose that the seasonal fluctuation of the groundwater table controls the vertical diffusion distance, and that the wide horizontal pollutant diffusion distance is a consequence of the sharp increase in the cohesive soil permeability (caused by repeated water gain and loss). [ABSTRACT FROM AUTHOR]

The effects of the concentration of total suspended solids from municipal wastewater on the water infiltration process in a clayey soil were investigated as well as the suitability of infiltration models with different numbers of parameters. The experiment consisted of columns of soil of 20 cm long in which supply water and synthetic municipal wastewater with different concentrations of solids were applied. The soil was characterized with respect to particle size, porosity, soil and particle density, clay water-dispersed clay, and infiltration capacity. The accuracy of the Kostiakov, Kostiakov-Lewis, Horton, Phillip, Green-Ampt, and Swartzendruber infiltration models was assessed by using the statistical criteria: mean error (MAE), mean squared error (RMSE), determination coefficient (R2), index of agreement (d), and Akaike information corrected criterion (AICc). The results indicate that the application of wastewater rich in suspended solids reduces the macroporosity of the soil, due to the clogging of the pores, causing a reduction in the hydraulic conductivity of the saturated soil and the cumulative infiltration. Based upon the AICc, the Kostiakov-Lewis models proved to be the most appropriate, except for the treatment with the highest concentration of solids, in which the Swartzendruber model presented the lowest AICc. In general, the other statistical criteria corroborate this conclusion. [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]

The primary consolidation may take long time due to the low permeability of clay soils in such cases soil improvement may be required to shorten the consolidation time, increase shear strength, and therefore bearing capacity. Preloading is one of the commonly used methods to consolidate soils before actual load and to strengthen weak compressible soils. In cases with time problems, the use of prefabricated vertical drains (PVD) with pre-loading shortens the drainage path and reduces the consolidation time by taking advantage of the horizontal permeability of the soils is generally higher. In this study, an embankment constructed at different load rates with constant accelerates and analyzes were performed for the non-drained and drained conditions of clay soils with PVDs are in 2m, 1m, and 0.5m intervals. In this way, the effect of load rate and PVD usage on consolidation settlement and excess pore pressures in underlying low permeable clayey soil was investigated. [ABSTRACT FROM AUTHOR]

Saturated/unsaturated pore water flow induced by rainwater infiltration in a soil column composed of a mixture of Toyoura sand and a small amount of clay (kaolin minerals) and the rinsing rate (mass transfer) of dissolved NaCl accumulated in the pore system from previous road salt application were investigated by experiments and simulations. Experiments were conducted with variable kaolin minerals mass contents (mixing ratios) in the soil columns. Measured saturated hydraulic conductivity (Ks) diminished with increased clay contents, i.e., Ks=0.00771, 0.00560, 0.00536, 0.00519, and 0.00314 cm s−1, for clay contents = 0.2, 0.5, 1, 2, and 5%, respectively. Experimental NaCl concentrations in the effluent from the bottom of the soil columns were about constant for times t ≈ 800, 1200, 1300, 1400, and 3400 s from the beginning of a rinsing experiment for the clay contents = 0.2, 0.5, 1, 2, and 5%, respectively. These NaCl concentrations then decreased with time quickly, and finally, approached zero. The presented model can reproduce experimental time variations of NaCl concentration in the effluent from the soil column reliably. Simulated salt mass left in the soil column with time also matches the experimental results for the clay contents = 0.2 and 0.5%. An inconsistency between simulated and experimental salt mass left in the soil columns becomes more significant as the clay content increases. These results suggest that the soil–water retention curve for the pure Toyoura sand can be applied to the soil column composed of kaolin minerals/Toyoura sand mixture when the clay content is small, i.e., less than 1%. Prediction of rinsing process becomes more difficult with increased clay content. However, the time required to remove saline water from the soil column to less than 1% of its initial value simulated by the model agrees closely with experimental results of 1000, 1500, 1700, 2100, and 5400 s, respectively. [ABSTRACT FROM AUTHOR]

Sandy soil has certain limitations such as low water holding capacity, high infiltration, high evaporation, and low soil moisture. To solve these problems, the addition of mycorrhizae and soil amendments to sandy soil could be able to improve the limitation. This study aimed to determine the effect of mycorrhizae and soil amendments on physical characteristics of sandy soil. The experiments were arranged using the CRD (Complete randomized design) method with two factors: doses of mycorrhizael and types of soil amendments. Doses of mycorrhizae consist of M0 (without mycorrhizae), M1 (mycorrhizae 3 spores pot-1), and M2 (mycorrhizae with 6 spores pot-1). The types of soil amendments consist of A0 (control), A1 (cow manure), A2 (biochar), A3 (clay soil), A4 (cow manure-biochar), A5 (cow manure-clay soil), A6 (biochar-clay soil). The results showed that mycorrhizae with cow manure-clay soil (M1A6) maintained the average of soil moisture seven days after harvest with an average of 12.65% and also reduced the rate of soil permeability three times than control. The combination of biochar-clay soil and mycorrhizae improved the water holding capacity and soil aggregation. Interaction of mycorrhizae and soil amendments improved the physical characteristics of sandy soil by increasing soil moisture and reducing soil permeability. [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]

Purpose: Biochar amendment is considered as a soil management practice worldwide for the sustainable agricultural production by improving soil physical property, fertility, and microbial activity. However, the change of soil structure and hydraulic conductivity over time after applying biochar to expansive clayey soil under field conditions are unclear. Materials and methods: In this study, biochar was applied to soil at the rates of 0% (CK), 1% (BC1), and 3% (BC3) (w/w) to assess the variation in soil physical properties after day 10, day 193, and day 375, respectively. Results and discussion: The results showed that the total soil porosity estimated based on bulk density and the average particle density of 2.65 g cm−3 was significantly higher than the total porosity as measured by water retention curve (P < 0.05). Compared with day 10, the measured total porosity at days 193 and 375 significantly decreased by 5.09% and 7.38%, respectively, under CK; however, that significantly increased by 2.14%/2.60% and 1.85%/3.60%, respectively, under BC1/BC3 (P < 0.05). The average bulk density in 1 year was significantly lower 3.30%/6.99% under BC1/BC3 than CK (P < 0.05). Compared with CK, soil pores (5–30 μm) significantly increased by 12.71% under BC3 and soil pores (> 300 μm) significantly increased by 114.25%/164.58% under BC1/BC3 after 375 days (P < 0.05). There were no significant differences in the saturated hydraulic conductivity among all treatments after 1 year (P < 0.05). Conclusions: Our findings indicate that the estimated total porosity is not suitable for evaluating the change of soil porosity over time after biochar application. Biochar in size less than 2 mm can improve soil structure in expansive clayey soil under field conditions. However, these positive changes may be insufficient to facilitate the improvement of saturated hydraulic conductivity after 1 year at the biochar application rates of 1% and 3%. Our findings provide insights into the application of biochar as a soil amendment for management practices in expansive clayey soil. [ABSTRACT FROM AUTHOR]

The current study aims to investigate the influence of the addition of fine materials on the engineering properties of silty sand soil. An intensive laboratory study of saturated and unsaturated silty sand soil treated with different percentages of fine materials of clayey soil (passing sieve #40 and ranging of 5, 10, 20, 40 and 80%) was investigated by conducting Oedometer and permeability tests. Unsaturated permeability and soil–water characteristics curve (SWCC) were also examined. Test results show that soil plasticity increases as the fine materials increase. The maximum dry unit weight (γ dmax) increased up to 10% of fine materials then decreased, while the optimum moisture content (OMC) increased along with the increase of fine materials. One dimensional compression test results show that the fine materials influence the compression characteristics and the compression index of the soil samples increased with the increase of fine materials. In contrast, the saturated permeability sharply decreased as fine materials were increased. For higher percentages of fine content, the reduction in soil permeability becomes less significant. In addition, the unsaturated permeability decreases with fine materials and suction pressure increases. The effects of fine materials are more evident at lower suction pressures. Furthermore, the water holding capacity and air entry value increased with the addition of fine materials. [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]

This paper presents a new modelling approach to quantify the hydraulic diffusivity of low‐permeability unconsolidated porous media under confined saturated‐flow conditions in the laboratory. The derived analytical solution for the transient variation of the hydraulic head after flow interruption was applied to experimental data obtained from continuous measurements of the water pressure at two locations in the soil column. Three soil samples made of a mixture of natural bentonite (at different mass fractions) and medium sand were studied during a series of stepwise constant flow rates of water. The numerical results well fit the experimentally measured decrease of the dimensionless hydraulic head. The study shows that the increase of the mass fraction of bentonite in the soil sample from 10 to 30% is accompanied by a strong decrease of the hydraulic diffusivity from 2.4 × 10−2 to 1.1 × 10−3 m2 s−1, which is clearly due to the decrease of the hydraulic conductivity of the soil sample. The specific storages obtained for each of the three samples are in the same order of magnitude and seem to decrease with the increase of mass fraction of bentonite. However, they clearly reflect the predominant portion of the compressibility of the porous medium compared with that of water. Compared with reported literature values for clayey soils, the specific storage values in this study are slightly higher, varying within the range of 2 × 10−3 to 8.1 × 10−3 m−1.. The experimental results also give insight into the limitations of the modelling approach. In the case of low‐permeability soils (K < 2 × 10−6 ms−1) and steady‐flow conditions with low Reynolds numbers, for example, Re < 0.003, it is recommended to choose a time duration for flow interruption between subsequent flow rate steps of longer than 5 s. For high‐permeability porous media, to increase the precision of the quantified hydraulic diffusivity, it might be useful to select a measuring frequency significantly higher than 1 Hz. [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]

Copyright of SDU Journal of Engineering Sciences & Design / Mühendislik Bilimleri ve Tasarım Dergisi is the property of Journal of Engineering Sciences & Design and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Clayey soils rich in smectite are commonly utilized for the construction of liner materials in engineered landfills owing to their low hydraulic conductivity. However, due to the high swelling potential of such clayey soils, their hydraulic conductivities are adversely influenced by desiccation cracking. In addition to cracks, the hydraulic conductivity of the clayey soils might also be affected by the complex composition of landfill leachate. The current study aims, therefore, to assess the effects of desiccation-induced cracks and leachate infiltration on the hydraulic conductivity of natural and 30% olivine-treated marine clay specimens. Clay specimens were prepared using three compactive energies and subjected to cycles of drying–wetting and hydraulic conductivity testing using tap water and field leachate as the permeants. Test results demonstrate significant improvements in the hydraulic conductivity of the olivine-treated clay samples after cycles of drying–wetting upon permeation with water and leachate. These improvements are attributed to the formation of magnesium–aluminate–hydrate and magnesium–silicate–hydrate gels as confirmed using microstructural analyses. The gels are responsible for minimizing the adverse impact of cracks on the hydraulic conductivity of the treated clay specimens. The findings indicate that olivine can be employed as a suitable additive in decreasing the hydraulic conductivity of soils prone to cracking. [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]