Soil Particle Diameter Research Articles

Humic acid application on soil stability indices and enzyme activity at different bell pepper water requirements

Use of organic materials helps in reducing the consumption of chemical fertilizers, contributing to the sustainability of agricultural ecosystems. Humic acid can improve soil structure, especially in soils with low clay content, aiding in water retention and enhancing water absorption by plants. This characteristic has led to the attention of humic acid application in drought stress, particularly in arid soil regions. The present study aimed to investigate the simultaneous effects of humic acid and plant water requirements on the physical and biological properties of soil under bell pepper cultivation. The factorial experiment was conducted in a completely randomized block design with three levels of humic acid: 0 (HA0), 2 (HA2), and 4 (HA4) g/Kg of soil and four levels of plant water requirements: 60 (L60), 80 (L80), 100 (L100), and 120 % (L120), with four replications under greenhouse conditions. Bell pepper seedlings were transferred to 10 Kg pots after applying humic acid treatments and after the establishing of seedlings, plant water requirement treatments were applied for 80 days. During this period, plants were maintained at a temperature of 25 degrees Celsius during the day, 18 degrees Celsius at night, and a relative humidity of 75%, with a carbon dioxide concentration of 80 milligrams per liter. The results of this study showed that treatments L80HA4, L100HA4, and L120HA4 had the most significant impact on improving soil physical properties, such as normal stability index, total soil stability index, mean weight diameter of soil particles, soil particle stability, geometric mean diameter of soil particles, and reduction in soil particle destruction percentage. The highest values of wet and dry weight diameter of soil particles were observed in treatment L100HA4, which were 42.92%, 74%, and 67.01% higher, respectively, compared to the control (L60HA0). In contrast, the highest percentage of soil particle destruction was observed in treatment L60HA0, showing a 32.90% increase compared to treatment L100HA4. Furthermore, the best performance of bell pepper yield was observed in treatments L80HA4, L100H4, and L120HA4, although the differences between treatments were not statistically significant. The application of humic acid, in addition to improving bell pepper yield, increased water use efficiency and reduced water use. The lowest yield (3283 Kg/ha) and the lowest water consumption (3584 cubic meters/ha) were observed in treatments L60HA0 and L60HA4, respectively. Additionally, the results showed that the highest water use efficiency observed in L80HA4 treatment (7.45 Kg/m³), while the lowest was in L60HA0 treatment (0.80 Kg/m³). Moreover, humic acid significantly influenced the activity of soil enzymes, including soil phosphatase and urease. With more application of humic acid, soil moisture retention, microbial biomass carbon, urease, phosphatases activities increased. However, in treatments with full water requirements and 20 percent more than plant water requirements, enzyme activities decreased.

The effect of maximum diameter of geogrid-reinforced sandy soil particles on shear strength parameters

Geogrid reinforcement is an effective method for improving the strength characteristics and bearing capacity of granular soils. The dimensional ratio of the diameter of soil particles to the mesh size of geogrid apertures can be effective on the strength performance and stress- deformation of the reinforced soil. To explore these factors, a sandy soil sample from Tonekabon (Iran) was separated into three gradations with a maximum particle diameter of 4.75, 2, and 0.425 mm, with an average relative density of about 57%. The samples were reinforced with two types of polyvinyl chloride (PVC) mesh as a geogrid, with aperture dimensions of 5 and 3 mm. All the samples were subjected to compressive loading in the triaxial shear apparatus under effective stress conditions. With a relative increase in the mesh size of the geogrid aperture to the maximum dimension of the reinforced soil grains, the internal friction angle decreased. Moreover, reinforcement of non-cohesive sandy soil caused apparent cohesion in the consolidated undrained conditions, and this was more evident with the reduction of the maximum diameter of sand particles. Decreasing the maximum diameter of the particles from 4.75 to 0.425 mm in the unreinforced and reinforced conditions caused the internal friction angle of the soil to drop by about 8%–10%. For the non-cohesive sandy soil, the results showed that soil reinforcement caused a more salient apparent cohesion in the soil with the maximum diameter of smaller particles. The sand passing through sieve #40 (0.425 mm) showed a cohesion of 0.2 to 0.34 kg/cm2 upon reinforcement with both types of meshes, while the soil lacked significant cohesion in the unreinforced conditions.

Numerical Simulation of Ground Subsidence Factors Resulting from Unpressurized Pipeline Rupture Below the Water Table

The rupture of an unpressurized pipeline below the water table can lead to the leakage of groundwater along with soil particles into the pipeline. This not only causes blockages in the pipeline but, more critically, can result in ground subsidence. Understanding the factors influencing this phenomenon is a subject of great interest. To delve into this matter, this study employs the DEM-CFD methodology to synergistically encompass particle dynamics and interactions within the flow domain. It introduces an innovative framework for simulating water and soil erosion subsequent to the rupture of subaqueous unpressurized pipelines. This pioneering approach introduces a novel modeling and simulation paradigm catering to the analysis of intricate phenomena of this nature. Upon validating the flow field, our investigation specifically focused on three key factors: particle friction coefficient, groundwater level, and particle size distribution. We conducted a thorough examination of the process and mechanism of water and soil loss at the pipeline leakage point and the subsequent development of stratum subsidence. Our results indicate that particles with a friction coefficient of 0.6 had a reduced maximum displacement by 8.9%, compared to particles with a friction coefficient of 0.3. Similarly, a groundwater depth of 2 m resulted in a 29.6% decrease in maximum displacement compared to a 4 m depth, with a corresponding 160.9% increase in maximum force chain strength. Discontinuous particle gradation, in contrast to continuous gradation, yielded a notable 40.3% reduction in maximum displacement and a substantial 495.1% increase in maximum force chain strength. This underscores the noteworthy influence of particle friction coefficient, groundwater table elevation, and soil particle diameter on the stability of the overlying soil strata in the vicinity of a compromised unpressurized conduit.

Experimental investigation of parametric changes in seepage time and length into the subsoil of hydraulic structures

Dams and hydraulic structures are built on rivers in order to protect water resources due to global warming, to collect surface waters to provide drinking water and/or irrigation water, to prevent floods and to establish hydroelectric power plants. Dams, for example, are hydraulic structures that have more or less positive or negative environmental interactions on surface water and groundwater. One of the environmental interactions of dams and similar hydraulic structures is the seepage of accumulated water in its reservoir from upstream bottom of the dam. This seepage can affect the level and location of groundwater, reduce the accumulation of water in the reservoir, and cause piping in the ground below the construction of the dam body. In order to control the seepage, the methods of increasing the seepage length by using sheet pile and clay blanket on the dam foundation are frequently used. In this study, in the physical laboratory model, the variations in the seepage lengths that occur under the hydraulic structure section in the soil with two different grain diameters of 0.85 mm and 1.5 mm, depending on the dam structure, soil and barrier structures (sheet pile and upstream clay blanket), were experimentally investigated. As a result, it was determined that the seepage occurs less in the soil with a smaller grain diameter of 0.85 mm, the smaller the soil particle diameter has a reducing effect on the seepage, and the use of sheet pile increases this effect positively. In addition, it has been determined that the clay blanket in the upstream is effective compared to the general conditions, but the use of sheet pile provides the most efficiency.

Freeze–thaw process of soil between two piles as monitored by piezoelectric ceramic sensor

As the mechanical properties of soil are affected by the moisture content, diameter of soil particles, and the soil temperature, we used piezoelectric ceramic sensors to monitor the freeze–thaw cycle of different soils at different temperatures and different moisture content. By studying the energy attenuation of stress waves propagating in freezing–thawing soil, its mechanical strength was determined. The results showed that the duration of freeze–thaw process was related to soil type and initial water content. For the same water content and larger soil particle size, the received signal amplitude and energy are larger. For the same soil type and higher water content, the received signal amplitude and energy are stronger. This study provides a feasible monitoring method for infrastructure construction in areas with complex geological conditions, such as Qinghai-Tibet frozen soil.

Attachment and detachment of large microplastics in saturated porous media and its influencing factors

Groundwater contamination by microplastics (MPs) has been gradually regarded as a potential human health risk, which calls for detailed investigation of MPs transport behavior in saturated zone. In this study, a series of sand column experiments were carried out to investigate the transport characteristics of large MPs with its diameter of 10–20 μm in porous media, in which the effects of different hydrological conditions and MPs characteristics were examined. Experimental results showed that the increase of water flow rate from 2.2 to 7.5 mL/min significantly increased the maximal outlet MPs concentration by two orders of magnitude, while a larger ratio of MPs diameter to soil particle diameter decreased its mobility. The increase of water salinity from 0 to 25 mmol/L (NaCl) decreased the maximal outlet MPs concentration by 50.5–68.4% for different sized MPs. Since chemical aging would lead to the formation of oxygen-containing functional groups and make MPs more negatively charged, it greatly increased the maximal outlet MPs concentration by 0.53–5.67 times. Compared with the traditional attachment model (AM), the attachment-detachment model (ADM) could better simulate the gradual desorption of large MPs from soil in the process of clean water flushing, indicating the nonnegligible detachment of large MPs from soil. In ADM, the desorption coefficient gradually decreased in the process of clean water flushing, which was only 31.6% of the initial value after flushing kept for 10 PV. Moreover, the equations to calculate the adsorption and desorption coefficients of MPs in the saturated zone were developed, which considered both MPs and aquifer characteristics. Results from this study described the desorption of large MPs in porous media under various conditions, which expands our knowledge about the fate and risk of MPs in underground environment.

Study of natural gas emission from a hole on underground pipelines using optimal design-based CFD simulations: Developing comprehensive soil classified leakage models

Gas leaks from natural gas pipelines can lead to catastrophic incidents, especially in the case of sour natural gas owing to the combination of its toxicity and flammability. As a safety consideration, these pipelines are underground to protect humans and installations. However, no comprehensive model has yet been proposed that can predict the leakage rate from the damaged buried pipelines in a wide range of influential factors. In this work, to compensate for this shortcoming, a set of soil classified models are presented considering the emission of sour natural gas in silty, sandy, and gravelly soils using the results of optimal design-based CFD simulations. In this way, a wide range is selected for effective factors of pipe pressure (2–100 bara), leakage hole diameter (2–40 mm), pipe diameter (4–56 in), soil porosity (0.3–0.45), and soil particle diameter (0.002–40 mm). These ranges cover the specifications of both urban distribution pipeline systems and transmission ones. A two-step solution strategy is implemented to consider the effect of pressure drop on the leakage rate. The CFD simulations are in good agreement with experimental data reported in literature. The leakage models are capable to predict the results of random simulations with a mean absolute percentage error of 13%, 9%, and 7.7% for silty, sandy, and gravelly soils, respectively, over a wide range of pressure and leakage hole diameter. Furthermore, the effects of soil mass properties and pipe wall thickness on the leakage process are investigated. To clarify the effect of soil mass on leakage rate, the CFD analysis of an aboveground leaking pipe is also performed comparatively.

Prediction of saturated hydraulic conductivity of sandy soil using Sauter mean diameter of soil particles

AbstractSaturated hydraulic conductivity of soil, Ksat, is a critical parameter for mathematical modelling of groundwater and soil water flow. Current empirical Ksat models, such as Kozeny–Carman model, Hazen models, or empirical approaches based on soil pedotranfer functions (PTFs) rely on the specific surface area, certain characteristic particle size(s), for example, d5, d10, d15, d50, etc., or the fractionation of sand, silt and clay. In this study, we proposed an alternative modelling framework to estimate Ksat from void ratio and arithmetic mean diameter of soil particles. We suggested to describe the particle size distribution (PSD) using a continuous mathematical distribution function, for example, the lognormal distribution function, and to obtain the Sauter mean diameter (dS) by calculating the moments of the PSD function. The proposed empirical equations were tested against the measured Ksat values for 54 sand samples with available measured PSD and void ratio as reported in Toumpanou et al. and validated using 49 sandy soil samples obtained from the Unsaturated Soil Database (UNSODA). We found that the dS was more relevant to Ksat than the number mean diameter (dN) and mass mean diameter (dM) (the RMSE was 0.486 for Ksat ‐ dN; 0.187 for Ksat ‐ dS; and 0.212 for Ksat ‐ dM, respectively). We also found that the proposed equation with dS had superior performance over the Hazen equation and PTF‐based models. Our results indicated that the Ksat calculated using dS, which was either estimated from discrete experimental data or calculated from a continuous lognormal PSD function, best matched with the measured values for coarse‐textured soils. Future studies should focus on developing empirical relationships for soil water retention curves and other soil properties based on continuous PSD functions.Highlights A modelling framework to estimate Ksat from the void ratio and arithmetic mean diameter is proposed. Sauter mean diameter, dS, can be obtained by calculating the moments of the PSD function. Ksat model using dS performs better than that using dN, dM, d5, d10, or d50 or PTF‐based models.

A modified aeolian flux model applicable for various soil particle characteristics

The aeolian flux is a key controlling factor for aeolian geomorphic evolution and the spatial redistribution of matter on the surface of the Earth and other planets. Based on theoretical derivation and a series of wind tunnel experiments, a non-linear positive correlation relationship is found between aeolian flux and the average diameter, sorting coefficient, density and sphericity of soil particles. Subsequently, a modified aeolian flux model containing these characteristic parameters of soil particles is proposed. For a wide range of the values of particle characteristic parameters, the prediction ability of the modified model for aeolian flux is satisfactory. These findings substantially deepen the understanding of the influence of soil particle characteristics on aeolian flux, and the modified model significantly improves the ability to predict aeolian flux, which will have an important impact on the aeolian geomorphic evolution, blown-sand disaster prevention and soil wind erosion control in the future.

Evaluation of the significance of the contact model particle parameters in the modelling of wet soils by the discrete element method

Modelling of the tillage process by working tools based on the method of discrete elements is currently the most promising. The results of modelling the processing process obtained by the method of discrete elements adequately describe the behaviour of the soil. Due to the large number of physical and mechanical parameters included in the description of contact models of discrete elements, the calibration process takes a lot of time. Thus, we set a research goal - to evaluate the significance of the parameters of the contact model particles in soil modelling by the discrete element method and to obtain nomograms for selecting the parameters of the Hertz-Mindlin contact model particles depending on the humidity of various types of soils. The article presents the results of calibration of the physical and mechanical parameters of the particles of the soil medium model described by the discrete element method. An improved Hertz-Mindlin JKR model was used as a contact model, the model was implemented in the Rocky DEM programme. The following properties of the modelled particles are taken as the studied factors – Poisson's ratio, static and dynamic friction coefficients, Jung's modulus, surface energy, and particle diameter. The detection of the natural slope angle of the soil was carried out for black soils of clay, light loam and sandy loam mechanical composition. The calibration was performed according to the angle of the natural slope. Comparison of the simulation results with field experiments of typical soils made it possible to establish that the nature of the change in the angle of the natural slope of the simulated soil environment is significantly affected by the surface energy and the diameter of the particles. The obtained dependences of the angle of natural slope on soil moisture and surface energy allow determining the parameters for the Hertz-Mindlin contact model as a function of humidity for Black soil zones of clay, light loam and sandy loam mechanical composition. Based on the results of field and model experiments, a nomogram was obtained that makes it possible to select parameters for the contact model - the diameter of soil particles and the value of surface energy depending on humidity and soil type. The obtained values of the parameters of the particles of the soil medium make it possible to simulate the process of tillage, optimize the design and technical parameters of the newly created working parts of tillage machines.

Analysis of complex erosion models and their implication in the transport of Pisha sandstone sediments

Coarse sediment of the Yellow River in the complex erosion area of the Pisha sandstone region of the Ordos Plateau is deposited on the downstream riverbed, posing a threat to the flood control safety of the river. The objectives of the present study were to analyze the mechanisms of combined erosion and sediment yield under the synergistic action of multiple dynamics, employing the indoor artificial rainfall-wind-freezing-thawing cycle solid model test to explore the temporal and spatial variation of the coarse sediment production and the transportation process. In this study, complex erosion indoor tests were carried out through the artificial rainfall-wind-freezing-thawing cycle solid model. The enrichment rate (ER), fractal dimension, and median diameter (d50) of soil particles were used to quantify the size distribution characteristics of sediment particles under different erosion dynamics. The coarse sediment was first transported in the process of soil erosion because of the special texture and terrain characteristics of Pisha sandstone soil. Moreover, the degree of heterogeneity of sediment under complex erosion was larger than that under water erosion. The effect of wind could aggravate the instability of the erosion dynamic system. Under the combined action of freezing-thawing, wind, and water, the particle size composition changed greatly, and the erosion energy was extremely unstable. The effect of complex erosion created conditions for the coarse sediment transportation. Under the freezing-thawing-wind-water combined action, the particle size of eroded sediment was the coarsest, and that of water erosion was the smallest. We concluded that the reason why the Pisha sandstone area has become the core area of the concentrated source of coarse sediment in the Yellow River is related not only to the special nature of the Pisha sandstone soil itself but also to the effect of complex erosion.

Designing of homemade soiling station to explore soiling loss effects on PV modules

Due to soiling on Photovoltaic modules, the active area reduces causing loss in short circuit current of the device due to lower light transmittance. Soiling on Photovoltaic modules depends upon environmental factors like wind, humidity, dust composition, tilt angle, orientation, and material of the module. Soiling loss studies conducted in outdoor conditions are unreliable as environmental factors are uncontrolled and vary with time hence there is a need to explore an indoor soiling station having controlled environment and stimulated conditions. This study reports an indoor soiling station with controlled environment capable to simulate the daily outdoor soil cycle in few hours. The designed soiling station is featured with cost reduction, design improvements, and automation that has been designed to simulate the soiling effects to study the effects of environmental parameters under desired and controlled conditions. The proposed soiling station is capable to explore optimized soiling loss effects on Photovoltaic modules by varying tilt angle, humidity, wind speed, and temperature. The soiling uniformity in the soiling chamber was confirmed by using Scanning Electron Microscopy and ultraviolet–visible spectroscopy while average diameter of soil particles was found to be 8.21 µm. The daily cycle of outdoor conditions has been performed on the module and it was found that after 7 daily soil cycles, the module lost 33.54% of short circuit current. In future work, same soiling station will be utilized to study effect of anti-soiling coating, economics of different cleaning processes, and the soiling loss at variable humidity, wind speed, and tilt angle.

Effects of reclamation methods and habitats on macrobenthic communities and ecological health in estuarine coastal wetlands

This study compared the community structure of macrobenthos in bare tidal areas and vegetated regions under two reclamation patterns, fully enclosed and opened reclamation, in Yangtze wetland, China. Compared with fully enclosed reclamation areas, opened reclamation areas had higher water salinity, higher number of species and abundance, and less disturbed habitat health status. Compared with bare tidal areas, vegetated regions were more suitable for the survival of macrobenthos and its habitat health status was more stable. Salinity, pH and larger soil particle diameter were positively associated with macrobenthic diversity, while total nitrogen and total phosphorus were negatively associated. Overall, compared with fully enclosed reclamation and vegetated regions, opened reclamation and bare tidal areas had less negative effects upon macrobenthic community and habitat health. Opened reclamation is preferred for wetland reclamation, and planting indigenous plants and releasing species adapted to fresh water is beneficial to the restoration of macrobenthic communities.

Predicting soil water content using support vector machines improved by meta-heuristic algorithms and remotely sensed data

ABSTRACT Soil water content characteristics included field capacity (FC) and permanent wilting point (PWP) are key soil indicators to study permeability, soil water retention capacity, drainage, irrigation, plant water stress and solute movement. It is necessary to use an appropriate model for predicting these characteristics because of the hardness of their measurement. The present research shows a comparison of intelligent models included ANN, ANFIS, SVM and SVM optimised by firefly and particle swarm meta-heuristic algorithms (SVM-FFA and SVM-PSA) to predict soil water content at −33 and −1500 kPa matric potentials in agricultural soils. Results showed that the SVM-PSA and SVM-FFA hybrid models presented the best performance rather than the others, with predictor variables included geometric mean diameter (dg) of soil particles, bulk density, organic carbon, NDVI and NSMI and the values of R2 and NRMSE in validation dataset, 0.94, 0.081, 0.96 and 0.077 for FC and PWP in SVM-PSA, respectively, and 0.96, 0.079, 0.97 and 0.075 for FC and PWP in SVM-FFA model. Therefore, these intelligent machines are preferable for accurate prediction and could be used to predict soil water content of soils with different soil textures in other regions of Iran or even the world.

Analysis of soil aggregates contaminated by 137Cs via particle size classification and X-ray diffraction

We subjected 137Cs-contaminated soil to stirring and particle classification to reduce the contaminated soil volume. 137Cs activity as a function of particle diameter changed drastically as the weight ratio of soil/water varied; 85% of all 137Cs was adsorbed to particles of minimum diameter after stirring. Soil argillites (smectites, vermiculites, and illites) adsorbed 137Cs. We used X-ray diffraction (XRD) analysis to measure the soil contents; the 137Cs distribution as a function of soil particle diameter mirrored the smectite levels revealed by the XRD peak intensities. Thus, smectic was the main absorbent of 137Cs.

Simultaneous prediction of several soil properties related to engineering uses based on laboratory Vis-NIR reflectance spectroscopy

The conventional methods for measuring soil properties are time-consuming and expensive. Over the past few decades, reflectance spectroscopy has been widely applied as a rapid and cost-effective technique to estimate soil properties. However, less attention has been given to estimating soil engineering properties using soil spectral data. To evaluate the efficiency of the technique, selected physical and mechanical properties of 220 soil samples from two study areas in Ghorveh-Dehgolan and Zrêbar regions in the Kurdistan province, west of Iran, were measured by standard laboratory methods. Spectral measurements were also performed on air-dried soil sub-samples using a laboratory spectroradiometer apparatus. After recording the spectra, the different pre-processing methods were tested to improve the estimations. Partial least squares regression (PLSR) was used to establish relationships between soil engineering properties and the spectra transformed via Savitzky–Golay first derivative. Based on the results, the prediction accuracy was very good for clay activity (Ac) and clay content (modeling efficiency (EF) = 0.75 and the ratio of performance to deviation (RPD) > 2), and good for cation exchange capacity (CEC) and effective diameter size (D10) (EF > 0.68 and RPD > 1.81). Reasonable predictions were also obtained for Atterberg limits, silt and sand contents, particle density (PD), diameters corresponding to 30% and 60% finer (D30 and D60, respectively), median particle size (D50), and geometric mean diameter of soil particles (dg) and their standard deviation (δg) (EF: 0.51–0.67, RPD: 1.44–1.76); however, the total porosity (n) and bulk density (BD) of soils were poorly predicted. The reliability and good quality of the estimations was probably due to the variability in the properties of the different soils collected from the two distinct geographical regions. Overall, the results confirmed the potential efficacy of Vis-NIR spectroscopy for a rapid estimation of different important soil engineering properties.

The Dependence Between Shear Strength Parameters and Microstructure of Subgrade Soil in Seasonal Permafrost Area

Permafrost and seasonal permafrost are widely distributed in China and all over the world. The failure of soil is mainly shear failure, and the strength of soil mainly refers to the shear strength. The two most important parameters of shear strength are cohesion and angle of internal friction. In order to ensure the sustainability of road construction in seasonal permafrost area, the microstructure of subgrade soil was observed and analyzed. First, three subgrade soils with different plasticity indices were prepared for triaxial test and scanning electron microscope (SEM). Then, these specimens underwent freezing–thawing (FT) cycles and were obtained shear strength parameters by triaxial shear test. Next, the microstructure images of soil were obtained by SEM, and the microstructure parameters of soil were extracted by image processing software. Finally, the correlation method was used to analyze the dependence between the shear strength parameters and the microstructure parameters. Results revealed that subgrade soils with a higher plasticity index had higher cohesion and lower angle of internal friction. In addition, with the increase of the number of FT cycles, the diameter and number of soil particles and pores tend to increase, while the roundness, fractal dimension and directional probabilistic entropy of particles decreased. With the increase of the plasticity index, the particle and pore diameter decreased, but the particle and pore number increased. Besides, particle roundness had the greatest influence on the cohesion and angle of internal friction of shear strength parameters.

Characteristics and Influencing Factors of Polycyclic Aromatic Hydrocarbons in Surface Soils from Typical Industrial Areas of Chengdu

To improve the pollution signature database for polycyclic aromatic hydrocarbons (PAHs) in typical industrial areas in China, surface soil samples were collected from four typical petroleum-processing industrial areas of Chengdu. The concentration and composition of 16 PAHs listed for prior control by the United States Environmental Protection Agency (US EPA) were determined using high-performance liquid chromatography (HPLC). The result showed that the concentration of PAHs in surface soils of the four industrial areas ranged from 191.2 to 1604.2 μg·kg-1, with an average of (583.6±365.6) μg·kg-1. The PAHs in the present study were mainly composed of medium-molecular-weight PAHs and high-molecular-weight PAHs. Among the PAHs detected in the study soils, phenanthrene (PHE), pyrene (PYR), fluoranthene (FLT), and benzo[b]fluoranthene (BbF) were the major pollutants presenting a potential pollution risk. Selected mathematical statistical methods were used to analyze the relationship between soil organic matter (SOM), soil particle diameter and PAH content, and to simultaneously identify the factors influencing PAHs in the soils. SOM was shown to be a favorable absorbent, predicting the migration and transformation behavior of PAHs in surface soil and soil ecological risk (i.e., PAH carcinogenicity) to some extent. Compared with SOM, the correlation between PAHs and soil particle size was relatively low, showing a weak positive correlation with silt, a weakly negatively correlation with clay, and no significant correlation with sand. These results provide a basis for soil remediation practices and further research in such industrial areas.

Shear-Induced Failure and Static Liquefaction in Reinforced Soil and Triaxial Tests

In the Federal Highway Administration (FHWA) laboratory, a phenomenon was identified that reduces soil bearing capacity. This phenomenon arises in common situations, for example, reinforced soil, triaxial tests, mat foundations on sand over bedrock, and other stratified media. In reinforced soil, this reduction is based on reinforcement spacing S and soil particle diameter D. This study provided a generic derivation showing that Coulomb’s failure criterion is triggered by shear stress associated with not only S and D, but also the other dimensions of a soil structure. Although identified and validated in experiments, the S:D instability was verified by finite-element analysis when the number of elements equals the number of soil particles. Static liquefaction was identified with instability and collapse of force chains. Although analysis was performed in the idealized context of unfaced soil structures, FHWA test data demonstrated violent effects on faced structures when the S:D stability limit was exceeded. For narrow structures, this study also evaluated the S:B instability, where B is the breadth of the reinforcement, triaxial test specimen, or foundation mat.

Portable wind tunnel experiments to study soil erosion by wind and its link to soil properties in the Fars province, Iran

Soil erosion controlled by the wind effect on the surface, has been largely studied by field in-situ measurements as well as laboratory or numerical simulations. Nevertheless, more in-situ measurements and observations are needed to document this phenomenon for various desert areas. In the present study, we focus on the documentation of different properties of a wide range of semi-arid and arid soils of the Fars province, and how they control the soil erosion by wind. By improving our knowledge on soil properties which lead to the limitation of soil erosion by wind, it will be possible to better prevent wind erosion in the Fars province. Extensive wind tunnel experiments were conducted in 20 different arid and semi-arid regions. For each region, three wind tunnel experiments were done to encounter local soil variability. We determined threshold wind speeds for which soil erosion was observed. Other experiments were conducted at the same high wind speed, and duration conditions, allowing discussing soil erosion rates by wind regarding soil properties. As already documented in the literature, our results pointed out a significant negative power relationship between wind erosion rate and different soil physical properties, including soil surface gravel cover, the mean weight diameter (MWD) of soil particles, and soil clay and moisture contents. Moreover, a nonlinear relationship as a power function was found between the increase of soil organic carbon and the decrease of soil losses by wind in the studied semi-arid and arid soils. We determined critical values of these soil properties for which wind erosion in Fars province is limited under high wind speed conditions. Additionally, the effects of the electrical conductivity (EC), sodium adsorption ratio (SAR), and calcium carbonate equivalent (CCE) on wind erodibility were discussed at low and high concentrations and for different soil textures.