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• Using in-situ measurements, size fractionation from soil to sediment was investigated for numerous calcareous soils. • The 0.2 mm was suggested as the boundary between high and low erodible fractions of calcareous soils. • Size range of 0.063–0.2 mm was found as the most susceptible fraction to wind erosion. • Soil fraction of 0.063–0.1 mm intensified calcareous soil potential for suspension-size sediment generation. • Critical values of various soil PSD criteria for wind erosion rate of calcareous soils were suggested. Soil texture and soil surface aggregate size distribution (ASD) are key factors to study soil erodibility by wind and sediment size distribution (SSD) in arid and semi-arid areas. However, less research has studied the effect of soil fractions on soil erodibility and wind-blown sediment size of calcareous soils. In the present study, we focused on the size fractionation and particle size distribution (PSD) of 60 calcareous soil samples collected from 20 semi-arid and arid areas in Fars province, southern Iran. Extensive in-situ wind tunnel experiments were conducted under controlled high wind speed to measure wind erosion rate (WER) and SSD. The results showed that the calcareous soils had different erodibility based on their PSD. Generally, the most erodible soils to the wind force were those with less than 10 % of clay and higher frequency of the 0.1–0.2 mm size class. However, when the soil clay content exceeds 20 %, ASD got dominated with the fraction of 0.4–0.8 mm and WER of the calcareous soils got limited. Besides, size range of 0.063–0.2 mm was suggested as the most wind erodible fraction of the calcareous soils. Furthermore, the mean weight diameter (MWD) of sediment particles averagely reduced 1.3 times as compared to that of the soil samples and WER got inhibited for regions in which the difference of soil and sediment MWD exceeded 0.05 mm. The SSD was significantly controlled by soil PSD and suspension-size sediments < 0.1 mm (SSS) were negatively proportional to soil clay, MWD, geometric mean diameter of soil particles (GMD), dry stable aggregates > 0.25 mm (DSA), and organic carbon as logarithmic equations. Moreover, the presence of the size fractions > 0.2 mm restricted the potential of calcareous soils to generate SSS, which would be quite beneficial for wind erosion combat and dust control of calcareous soils. [ABSTRACT FROM AUTHOR]

• Digital mapping of soil clay types was performed using easily accessible covariates. • Multiple linear regression and random forest algorithms were compared. • Random forest resulted in higher prediction performance. • Topography and soil properties mainly affected palygorskite and kaolinite variation. • Soil properties were considered responsible for the spatial distribution of illite. Understanding the abundance variability of clay minerals, as fundamental soil components, will help the users to improve land management and address concerns over climate change and soil fertility. Therefore, this investigation aimed to model the abundance and spatial distribution of clay types, including palygorskite, illite, and kaolinite, and identify the most significant variables affecting their variability using a digital soil mapping (DSM) approach in Darab district, southern Iran. Multiple Linear Regression (MLR) and Random Forest (RF) techniques were applied to link clay types and environmental attributes that were obtained from a Landsat-8 operational land imager (OLI) and digital elevation model (DEM). A ten-fold cross-validation approach was applied to calibrate and validate the models, and 50 bootstrap models were used to quantify the prediction uncertainty. The models accuracy was defined by the coefficient of determination (R2), root mean square error (RMSE), and the ratio of performance to the interquartile range (RPIQ). Findings denoted that the RF model better predicts the abundance and variability of clay minerals in the study area (R2 = 0.56, 0.47, and 0.48, RMSE = 5.3, 1.91 and 0.63 % and RPIQ = 2.82, 3.28 and 2.62 for palygorskite, illite and kaolinite, respectively). Based on the feature selection analysis, topographic covariates and soil properties determined palygorskite and kaolinite content variations, while for illite, only soil properties could explain the spatial distribution. Besides, the RF produced a lower uncertainty for palygorskite compared to the other clay types. The present research can provide new insight into the spatial variability of clay minerals in arid and semi-arid regions of Iran that could be extended to other similar environments. Moreover, the results showed that the easily available environmental variables could provide reliable predictions. However, other environmental covariates, such as XRF analysis, Vis-NIR, and MIR spectroscopy, are also recommended as input variables for further studies. [ABSTRACT FROM AUTHOR]

Pressuremeter Test (PMT) and shear wave velocity (Vs) are two important in-situ tests for determining soil deformation characteristics in different strain levels. The PMT is an expensive and time-consuming test that can measure pressuremeter modulus (E PMT) of soil and rock. The Vs is a low-cost test for determining soil deformation through the seismic method. So finding the relationship between PMT and Vs can be useful and cost-saving for cross-checking the parameters obtained by these two methods. In this study, 94 PMT and Vs tests were carried out on silty clay and clay soil from 3 sites in Iran, and the relationship between E PMT and Vs was investigated using regression analysis. Finally, the best statistical model for relationships was proposed according to the highest value of adjusted R2 and Fisher coefficient (F) and a minimum value of significance (Sig.). The results showed that there is a direct relationship between E PMT , Vs, and N 60 with depth then the soils with higher relative density are at the deeper layers. On the other hand, there is a linear significant relationship between E PMT and Vs for each site with R2 > 0.79. When the data for all three sites are considered together, R2 decreased to 0.62 but the overall trend of the data is similar. Due to the similarity of the soil of the three sites in terms of classification, minor differences in plasticity index and water content ranges in the three sites can be a reason to reduce the R2. The comparison between estimated E PMT based on proposed equations in the present study and measured E PMT shows that the normalized consistency ratio is generally close to zero (−0.09 < CR < 0.06) so the equations are valid and reliable. A comparison of the results of the present and a previous study showed that the change rates of E PMT and V S were similar so that the CR values are generally close to zero (−0.09 < CR < 0.09). The minor difference between the E PMT and Vs in each site in the present study and the previous research is due to the soil type and plasticity specifications. • PMT and V S are in-situ tests for determining soil stiffness in different strain levels. • There is a direct relationship between E PMT , Vs, and N 60 with depth. • There is a linear relationship between E PMT and Vs for silty clay soil. • The relationship between E PMT and Vs depends on the plasticity index. [ABSTRACT FROM AUTHOR]

We explore changes in magnetic susceptibility (χ lf), and various forms of Fe and ferrimagnetic minerals after incubation by crude oil in four different textural soils. Four soil classes: clay, sandy, silt loam and sandy loam, were collected in central Iran and incubated with 0, 2.5, 5.0, 7.5 and 10% w /w of crude oil at 80% moisture of field capacity for 1, 3 and 6 months. After each period of incubation, various forms of Fe using extraction techniques, χ lf and total petroleum hydrocarbon (TPH) were measured. In addition selected samples from the four soil types were analyzed by XRD for characterization of ferrimagnetic minerals. The results showed that all forms of iron and magnetic susceptibility increased significantly with increasing concentration of crude oil and incubation time. The highest dithionite extractable iron (Fe d), χ lf , as well as the ratio of Fe d to oxalate extractable iron (Fe o) were obtained for 10% w /w crude oil after 6 months incubation due to formation of ferrimagnetic minerals. The increase in the concertation of ferrimagnetic minerals (magnetite/maghemite) was verified by XRD. Significant positive correlations were obtained among χ lf , Fe d and TPH after 6 months of incubation. The results from this study confirm that magnetic methods can be used as a quick and cost-effective means for evaluation of TPH in polluted soils during the remediation, as compared to the chemical analyses. • χ lf and ferrimagnetic minerals following incubation with crude oil were studied. • Forms of iron showed significant difference among applied treatments. • Magnetic properties of the soil enhanced with increasing crude oil pollution. • Magnetite/maghemite were increased by pollution and incubation time. • Intensity of the peaks with χ lf in four soils showed high positive relationships. [ABSTRACT FROM AUTHOR]

Electro-osmosis is a phenomenon describing the motion of liquid adjacent to a charged surface under the influence of an electric field. Electro-osmosis is considered as an efficient soft soil improvement technique. In this study, series of laboratory tests were performed utilizing graphite and stainless steel electrodes under three levels of voltage gradients for 28 days using the soil from north of Iran to investigate the effect of various parameters on electro-osmotic and geotechnical properties. Moreover, the microstructure and chemical analyses of the soil before and after treatment gave an in-depth perspective to underlying mechanism of this process. Water drainage which has the most important effect on consolidation of soils, terminated after a few days. The termination time for stainless steel is smaller than graphite and the whole drained water volume is larger in case of stainless steel compared to graphite. The strength around the anode is larger than that of the cathode zone and the stainless steel electrode induced larger strength than the graphite electrode. The SEM images exhibited the agglomeration of the soil after electro-osmosis treatment, and some precipitation was also identified, which was attributed to iron based compounds. Chemical analysis illustrated that the concentration of calcium ions decreased around the anode and increased near the cathode while Fe and Al amount did not change significantly, implying the ion exchange and ion migration due to the electro-osmosis process. Additionally, the stainless steel electrode introduced iron and chrome ions to the soil, which affected structure and chemical distribution of the ions. • Electro-osmosis changed the microstructure of the soil and decreased the void volume of the soil. • The Calcium and Magnesium ions were substituted by iron and Aluminum ions and migrated through the soil. • The geotechnical properties of plastic soil improved. • The stainless steel electrode had better performance compared to graphite electrode. [ABSTRACT FROM AUTHOR]

• Invasion of the test soil clogged the space between the inner and outer pipes of the Hydroluis drainpipe in two weeks. • High flow velocity at the soil-envelope interface and low retention capacity caused poor function of the Hydroluis. • Based on Stokes' Law, the design of Hydroluis drainpipe is unsuitable for filtering fine silt particles (0.002 < D < 0.02 mm). • PP450 drainpipe showed good hydraulic and filter functions under the same laboratory conditions. Subsurface drains, when installed in non-cohesive soil, are typically covered with an envelope to tackle problems of clogging and siltation. Selecting a suitable envelope material, however, is complicated and depends primarily on soil characteristics in the area where the drains are to be installed. A new promising drainpipe-envelope concept, Hydroluis, has been developed which the designers claim works in a wide range of soils. The Hydroluis drainpipe consists of a corrugated inner pipe with three rows of perforations at the top and an unperforated outer pipe that covers the top two thirds of the inner pipe. We analysed the hydraulic and filter functions of this new drainpipe in a soil tank laboratory model with a saline-sodic problem soil from south-western Iran and compared Hydroluis performance with that of a locally-manufactured synthetic envelope material (PP450). The silty clay soil used in this study was 40 % clay, with a plasticity index (I P) of 16.9 and an exchangeable sodium percentage (ESP) of 60.4 %. The Hydroluis drainpipe clogged during the first two weeks of the test due to invasion of the test soil into the space between the inner and outer pipes. Of the substantial volume of sediment that entered the Hydroluis inner pipe, 38 % removed from the pipe in the first day. In contrast, the PP450 drainpipe showed good hydraulic and filter functions, entering very little sediment to drainpipe during the entire test period and stabilizing at drainage rate of 28 mm/day and entrance resistance of 55 days/m, at around day 50. Our analyses suggest that the clogging and poor drainage function of the Hydroluis drainpipe was caused by the higher flow velocity (21.5 times higher) at the soil-envelope interface of the drainpipe, in addition to the lower Hydroluis drainpipe's soil retention capacity (18 times lower) compared to the PP450 drainpipe. Assuming Stokes' Law governs filter function, the results of Hydroluis design evaluation also suggest that in stable soils, very fine sand or coarser soil particles (D > 0.05 mm) place no serious limitations for Hydroluis drainpipe application, whereas the current design is unsuitable for filtering fine silt particles (0.002 < D < 0.02 mm). In conclusion, we suppose the Hydroluis drainpipe does not perform well in silty saline-sodic soils, such as those found in south-western Khuzestan Province, Iran. [ABSTRACT FROM AUTHOR]

• Adhesion and clogging tendency of clay-rich soil and rocks were investigated using different test methods. • Correlation of normal adhesion to cohesion and tangential adhesion in various IC were investigated. • It was found that clayey material may encountered on the Tabriz subway lines have medium to high clogging risk. Clogging phenomenon is defined as the excessive adhesion of clayey particles to drilling equipment that adversely affect machine efficiency. This study involves the clogging potential of clayey soil and rock samples collected from Tabriz subway lines that were tested by laboratory experiments. In order to achieve the objectives of this study, a series of analyses were carried out including sieve analysis, hydrometer, Atterberg limit, slake durability, direct shear, modified direct shear test on the soil/steel interface, and piston pullout apparatus. According to USCS, the studied samples are classified as CL and CH. The clay minerals of the samples are mainly montmorillonite and illite. According to the exist diagrams and classifications based on Atterberg limits, consistency index and adhesion stress, samples are classified as medium to high risk for clogging. The maximum clogging occurrence is possible in the moisture content between 20 and 52% (IC < 0.75). The results proved that water content is a key parameter in adhesion stress variation and clogging behavior of clayey materials. The results of the direct shear test on clay/clay and clay/steel interface indicate that with increasing water content, the cohesion of soil decreases and tangential adhesion to the steel surface tends to increase. Based on piston pullout test, the normal adhesion stress of samples increased to a peak value at IC = 0.65 to 0.75. The results obtained in this study indicate a moderate to high risk of clogging in the mechanized excavation of subway lines in the study area while encountering clayey layers. [ABSTRACT FROM AUTHOR]

• Persian gum as a new source of carbohydrate polymer was used to improve soil. • Persian gum has acceptable strength results in comparison to xanthan and guar gums. • Strength achievement of Persian gum treated soil by moisture loss is considerable. • Persian gum is useful for permeability reduction due to its pore filling property. • High thermal stability for Persian gum treated soil was observed. Persian gum as a newly introduced source of carbohydrate polymers obtained from the trunk and branches of wild almond trees of Zagros forests in Iran, has found wide applications in food and pharmaceutical industry owing to its unique structure. However, its behavior in soil environment is still unknown. This paper proposes application of Persian gum to stabilization process of a low plasticity clayey soil. A series of macro and micro scale tests including unconfined compression strength, direct shear test, scanning electron microscopy imaging, Stereo zoom microscopy, Brunauer, Emmett and Teller tests, thermal gravimetric analysis and Particle size analysis were conducted on soil stabilized with different amounts of Persian gum. All defined tests were also conducted on previously studied soil additives, xanthan and guar gums. The results confirm the successful performance of Persian gum in binding soil particles, pore filling, thermal stability, soil fluctuation and formation of large particles in comparison to common hydrocolloids. [ABSTRACT FROM AUTHOR]

Nickel bearing soils derived from serpentinized ultramafic rocks are widely exposed as two parallel zones in Bavanat region along the Sedimentary Zagros Orogenic (SZO) and Metamorphic Sanandaj-Sirjan (MSS) belts. These laterites in the Mazayejan area of the Northern zone are divided into two groups; the in situ soils found mainly in the east, and the transported soils which are common in the west of the study area. The maximum Ni concentration of the studied soils is 1787 μg g−1. The main vegetation types of the area include open shrub lands and semi-desert steppes. Many soil characteristics in the study area are quite variable, such as Mg/Ca ratio, exchangeable metal fraction, extraction efficiency (EF), pH, organic content (OM), texture, and cation exchange capacity (CEC) as well as seasonal variation of Ni availability and metal transfer to plants. This study indicated that low Mg/Ca ratio (0.1–2.3 μg g−1), high carbonate content (up to 42.8 wt%) and very low exchangeable Ni fraction (0.01–0.34 μg g−1) result in low uptake of nickel by plants. Low EF, but high pH and OM result in Ni fixation in the soils, and consequently low Ni transfer factor to plants. Clay textured soils with high CEC (10.5 wt%) are characterized by the lowest transfer coefficient of Ni from soil to plant, due to the stronger adsorption of Ni in the soils. Ni concentration in living tissues change with the season, the leaves of the same plants investigated in autumn contain more Ni than in spring. As a result, plant sampling in autumn should be preferred for nickel exploration when using biogeochemical and other methods such as Ni phytoextraction, by selected plants. Unlabelled Image • Laterites in Bavanat are divided into in situ and transported Ni-bearing soils. • Soil properties and sampling seasons affect Ni availability and transfer to plants. • Low Mg/Ca ratio, EF and exchangeable Ni fraction result in low uptake of nickel by plants. • High pH, CEC, OM values and clay texture lead to low transfer coefficient of Ni to plants. • Plant sampling in autumn is preferred in mineral exploration. [ABSTRACT FROM AUTHOR]