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In the manufacturing of some sectors, such as marble and brick, certain byproducts, such as sludge, powder, and pieces containing valuable chemical compounds, emerge. Some concrete plants utilize these byproducts as mineralogical additives in Turkey. The objective of the experimental study is to ascertain whether the incorporation of waste from the marble and brick industries, in powder form, into cement manufacturing as a mineralogical additive or substitute is a viable option. The materials used in this study were marble and brick wastes, CEM I 42.5 N cement, CEM I 42.5 clinker, water and CEN standard sand. as a replacement for the cement and a substitution for the clinker, the waste marble sludge powder and calcined clay brick powder was separately replaced with either CEM I 42.5 N cement or CEM I 42.5 clinker To determine the usability of marble and brick wastes in conventional cement and clinker production. To this end, there were prepared twenty-four different binder constituents at 0, 6, 10, 20, 21, and 35%. Then the hardened mortar samples were prepared with the new twenty-four different binders, standard drinkable water, and standard mortar sand. Besides, to evaluate pozzolanic activity, the construction lime was mixed with the marble and brick wastes. The microstructure of the marble and brick waste was analyzed using X-ray fluorescence, scanning electron microscopy and energy dispersive spectroscopy. In addition to the microstructure analyses, the chemical features of the marble and brick wastes, including oxides, loss on ignition, pH, total organic content and clay content, were determined in accordance with current standards. The physical and pozzolanic features of the wastes, such as their fineness, density, specific surface area, water permeability, and flexural and compressive strengths, were also evaluated using up-to-date standards. The results of the chemical experiments indicate that the total oxides of calcium, silica, alumina, and ferrite in marble powder and brick powder are more than 54% and 82%, respectively. Marble powder and brick powder are more finely ground than a few mineralogical materials, such as fly ash and silica fume, according to the residue amounts on sieves. Consequently, marble and brick powders can be used as water reducers in mortar, grout, and concrete. Moreover, marble and brick powder have a higher density than many mineralogical materials, making them suitable for applications requiring a higher binder feature of cement, higher strength, and improved durability of mortar and concrete. The specific surface area and water permeability of the marble and brick powders provide compelling evidence to support the inferences previously made about the fineness and density of these materials. Additionally, the pozzolanic properties of the brick powder were three and fourteen times greater than those of the marble powder, as evidenced by its compressive and flexural strengths, respectively. It can be reasonably deduced from the experimental results that marble powder is a latent hydraulic mineralogical natural additive or substitute, while brick powder is an unnatural mineralogical pozzolanic additive or substitute for cement-making processes. [ABSTRACT FROM AUTHOR]

The process of permeation damage of the filling medium in the fracture is critical to the stability of the fractured rock mass. This study focused on the seepage failure process of filling materials in fractures and faults. To investigate the effects of axial stress and clay content, a series of experimental tests were conducted on internally unstable granular soil specimens with different clay contents under different axial stresses. The variations of flow rate and hydraulic conductivity were recorded and analyzed during the tests, and the typical process of seepage failure was summarized. The flow rate, hydraulic conductivity, and their growth rates were found to be smaller under high axial stress compared to low axial stress, and the flow rate of samples with higher clay content was smaller than those with lower clay content. Initially, the hydraulic conductivity decreased slightly due to clay and fine particle rearrangement, and remained nearly constant when the hydraulic gradient was small. However, as the hydraulic gradient increased, the hydraulic conductivity began to increase in response to the loss of clay and fine particles. [ABSTRACT FROM AUTHOR]

This study examines the factors influencing internal erosion and hydraulic conductivity in sand-clay mixtures used in earth structures. Internal erosion, defined as the dislodgement and transport of particles within the soil due to internal water movement, encompasses processes such as suffusion, backward erosion, and concentrated leak erosion. It is a major cause of failures in hydraulic geo-structures. Utilizing a modified triaxial apparatus, this research investigates the effects of gap ratio, fines content, clay-sized particle types, confining stress, and hydraulic loading conditions on soil erosion mechanisms. The findings highlighted the critical role of soil fabric in erosion behavior. Higher confining pressures (σ') generally reduce erosion ratios. However, excessive fines content can increase erosion under high stress due to the detachment of force-chain particles and subsequent erosion. Soils with higher fines content exhibit reduced pore connectivity, creating more tortuous paths and increased clogging, which can lower erosion rates compared to soils with lower fines content. The gap ratio affects erosion dynamics: smaller ratios lead to clogging and partial filtration, while larger ratios facilitate particle migration but may also cause collapse and arch formation, particularly in low-plasticity soils. Increased clay content enhances erodibility, resulting in more defined erosion paths and greater susceptibility to suffusion. The type of hydraulic loading also impacts erosion rates and channel formation. Incremental loading results in slower development of erosion pipes compared to linear loading, which forms more distinct erosion channels rapidly. [ABSTRACT FROM AUTHOR]

Abstract Thermal conductivity of moulding sands is very poorly known. In addition, the study of thermal conductivity variation of moulding sand as a function of its properties is a crucial step in the prediction of moulding defects. So, this study investigates the effects of moisture content, compactibility and permeability of green sand on its thermal conductivity variation, with a specific focus on the combination of bentonite, sand and water for thermal characterization of the transient hot-bridge (THB) method. Three levels of active clay content were selected: 8.1%, 8.98% and 10.03%. For each level of active clay, different mixes were made by varying the amount of added water. Compactibility, permeability and thermal conductivity tests were carried out for each combination of active clay and moisture contents. The experimental results show that thermal conductivity increases with water content and compactibility for different active clay contents, whereas thermal conductivity decreases with permeability, and this variation is highly significant especially for 8.07% of active clay content.

Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, Chengdu 610000, China) Abstract: In order to provide real-time suggestions for the safety of the lower Yellow River embankment, it was imperative to conduct a quantitative analysis of the SWCC for the Lower Yellow River embankments soils under varying confining stress conditions. By analyzing the relationship between clay content and SWCC of the embankment soil, a simple parameter model based on clay content and dry density was proposed. This model was then utilized to examine the SWCC under various confining pressures. The findings indicate that the SWCC exhibits distinct characteristics corresponding to varying clay content. Dehydration curves can be demarcated into different regions based on clay content, with an increase in clay content correlating positively with the magnitude of the hysteresis effect observed. The simple model based on clay content exhibits a good applicability to the dehydration curve of loamy and clayey soils with clay fractions exceeding 20%. As confining stress intensifies, the matrix suction associated with a given water content incrementally rises. The parameter e, associated with confining pressure, has been incorporated into the model, enabling the prediction of SWCC for the Lower Yellow River embankment under different load conditions. [ABSTRACT FROM AUTHOR]

This study aims to evaluate the factors controlling the sensitivity of fine-grained soils to seismic stresses and revise the criteria previously proposed by the authors to diagnose liquefaction. To this end, dynamic tests have been performed on artificial mixes as well as natural soils from a wide area of an earthquake devastated city (Adapazari) using two types of dynamic testing. Studies have led to findings suggesting that the gray area between susceptible and non-susceptible soils proposed by several investigators in the past can now be dispensed with. Although physical properties of fine-grained soil supply sufficient information for diagnosis, the dynamic simple shear test is found to be a convenient and rapid way to confirm the judgement. However, it has been seen that dynamic testing alone may not be the last word in the determination of liquefaction, and physical properties should also be addressed. Anomalies observed in test results are also discussed. Conclusions show significant differences from existing proposed criteria in the literature. [ABSTRACT FROM AUTHOR]

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The demand for nondestructive testing techniques (NDTs) that can be implemented continuously and cost-effectively for large-scale study purposes is increasing. Ground penetrating radar (GPR) as an NDT method permits the estimation of pavement materials characteristics without disrupting the serviceability of the system. This research used typical pavement materials for constructing load-bearing layers (base and subbase) for the GPR laboratory tests. A 2 GHz GPR antenna was applied to execute the tests by changing three essential variables of the material: water content, compaction and clay content. Machine learning and interactive methods were innovatively utilised to model the collected data. As a result, a multivariate non-linear empirical function is proposed by the interactive procedure. Furthermore, the machine learning modelling (SVM method) with R2 of 0.91 indicates promising results to evaluate the pavement layers' properties. Machine learning can enhance the speed and accuracy of analysis when faced with multi-variables and extensive data. [ABSTRACT FROM AUTHOR]

Thermal conductivity of moulding sands is very poorly known. In addition, the study of thermal conductivity variation of moulding sand as a function of its properties is a crucial step in the prediction of moulding defects. So, this study investigates the effects of moisture content, compactibility and permeability of green sand on its thermal conductivity variation, with a specific focus on the combination of bentonite, sand and water for thermal characterization of the transient hot-bridge (THB) method. Three levels of active clay content were selected: 8.1%, 8.98% and 10.03%. For each level of active clay, different mixes were made by varying the amount of added water. Compactibility, permeability and thermal conductivity tests were carried out for each combination of active clay and moisture contents. The experimental results show that thermal conductivity increases with water content and compactibility for different active clay contents, whereas thermal conductivity decreases with permeability, and this variation is highly significant especially for 8.07% of active clay content. [ABSTRACT FROM AUTHOR]

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]

Clay swell potential can be classified based on the value of activity and it is defined as the ratio of plasticity index to clay content as a percentage. This paper outlines the investigation into how activity correlates with other key properties of clayey soils. Specifically, four approaches were evaluated for predicting activity using: (a) liquid limit (LL), specific surface area (SSA), cation exchange capacity (CEC) and clay content; (b) LL, SSA and CEC; (c) LL; and (d) SSA and CEC. For this purpose, a database of 104 samples was collected from which 35 machine learning algorithms were trained. Gradient Boosting Trees showed the highest prediction accuracy in the four approaches and, to improve its prediction performance, a Bayesian Optimization was applied to tune theirs hyperparameters, resulting in the final models. The performance of the developed models was evaluated, showing prominent results with exceptionally good metrics, except in the approach from SSA and CEC where the trained algorithm was not capable of predicting activity with confidence (R2=0.46). This algorithm can predict activity using only LL with high accuracy (R2=0.94), and when combined with SSA and CEC, the precision is further enhanced (R2=0.96). [ABSTRACT FROM AUTHOR]

Shear strengths of silty soil were determined for shallow destruction of the soil sites frequently occurring in the Central Plains area. Specimens were prepared with five different clay contents (5, 10, 15, 20, and 25%) prior to compaction at dry densities of 1.60, 1.70, and 1.80 g/cm3. Soil specimens were saturated and then the consolidated undrained shear test was conducted with eight confined pressures ranging from 1 to 400 kPa. Results indicate that the shear strength increases significantly as the clay content increases from 5 to 25%, and the cohesion c shows bilinear function with the inflection point at the clay content of 10%. The difference of cohesion in the high and low stress sections decreases gradually to almost the same value until 25% of the clay content, while the internal friction angle φ decreases with the increase in clay content. Within the range of dry density and clay content tested, the shear strength of silty soil in the low stress range obtained is higher than the measured value. Therefore, for the shallow damage of soil site, the shear strength parameters should consider the low stress test conditions. The bilinear growth of cohesion c with clay content can be attributed to the changes from “sand-like soil” to “clay-like soil” with the skeleton of soil specimen transitioning from sand particles to “clay grid” when the clay content exceeds approximately 10% combined with the results of scanning electron microscopy.

Geological hazards such as gully erosion, collapse and slope failure occur frequently in loess areas, which are closely related to the soil disintegration characteristics. Understanding the impact of freeze–thaw and wet–dry action on soil disintegration in the context of climate change is essential to establish effective soil and water conservation strategies and prevent engineering geological hazards in loess areas. In this study, sodic–saline loessial soils with different clay content were subjected to freeze–thaw and wet–dry cycles, followed by aggregate durability tests, direct shear tests and disintegration tests to investigate the effects of the two natural processes on soil disintegration characteristics. The results showed that the samples subjected to freeze–thaw cycles primarily exhibited rapid and stable disintegration, followed by slow disintegration, whereas the samples subjected to wet–dry cycles revealed weight gain, continuous slow disintegration and eventual sudden disintegration. Freeze–thaw action continuously deteriorated the disintegration resistance of soil, while wet–dry action improved the disintegration resistance of soil after the first cycle, and gradually weakened it in subsequent cycles. Statistical analysis showed that, for samples undergoing freeze–thaw cycles, the number of cycles and clay content were positively correlated with the disintegration rate, while the aggregate durability was negatively correlated with the disintegration rate. For samples undergoing wet–dry cycles, the number of cycles had a positive effect on the disintegration rate, while the clay content, shear strength and cohesion had a negative correlation with the disintegration rate. At a certain clay content, there was a positive correlation observed between the surface crack ratio, crack length and width with the disintegration rate of the wet–dry samples, while shear strength and cohesion had a negative correlation with the disintegration rate of both freeze–thaw and wet–dry samples. Furthermore, the study outlined the disintegration mechanism of loessial soils based on internal factors, driving factors, resistance factors and evolutionary factors. This study contributes to the in‐depth understanding of the catastrophic mechanism of geological hazards in cold and arid areas and provides experimental evidence for its control and management. [ABSTRACT FROM AUTHOR]

One challenge in predicting soil parameters using in situ visible and near infrared spectroscopy is the distortion of the spectra due to soil moisture. External parameter orthogonalization (EPO) is a mathematical method to remove unwanted variability from spectra. We created two different EPO correction matrices based on the difference between spectra collected in situ and, respectively, spectra collected from the same soil samples after drying and sieving and after drying, sieving and finely grinding. Spectra from 134 soil samples recorded with two different spectrometers were split into calibration and validation sets and the two EPO corrections were applied. Clay, organic carbon and total nitrogen content were predicted by partial least squares regression for uncorrected and EPO-corrected spectra using models based on the same type of spectra ("within domain") as well as using laboratory-based models to predict in situ collected spectra ("cross-domain"). Our results show that the within-domain prediction of clay is improved with EPO corrections only for the research grade spectrometer, with no improvement for the other parameters. For the cross-domain predictions, there was a positive effect from both EPO corrections on all parameters. Overall, we also found that in situ collected spectra provided an equally successful prediction as laboratory-based spectra. [ABSTRACT FROM AUTHOR]

Electrical resistivity (ER) method, non-destructive approach determining subsurface anomalies by leveraging electrical properties. In-situ ER is popular owing to its quick, reliable and continuous subsurface data, although heterogeneity across horizontal and vertical orientation is less explored. In this regard, present study tends to understand this effect by carrying out small-scale laboratory ER tests focusing on how varying vertical soil layer positions impact resistivity. Two distinct soil types with varying resistivity were arranged in both perpendicular and parallel direction to current flow, where low and high resistive layers were placed adjacent to one another. Results derived from study indicated that placement of low resistive soil before high resistive one leads to 37.58 % reduction in resistivity. Furthermore, parallel alignment resulted in 9.89 % decrease compared to perpendicular layering. Thus, these findings tends to highlight significance of layering in influencing resistivity values and underscoring the complexity of electrical resistivity testing. [ABSTRACT FROM AUTHOR]

Fertilization regimes have been widely practiced to increase soil organic carbon (SOC) in Chinese farmland, but the findings of various studies are often widely divergent. Therefore, a comprehensive review of the impacts of fertilization regimes on SOC is needed. In this study, a meta-analysis based on 57 peer-reviewed articles was conducted to examine the effects of fertilization regimes on SOC in China. On average, the inorganic fertilizer combined with organic fertilizer regime (NPKOF) represented the most effective approach, increasing SOC by 42.6%; this was followed by the organic fertilizer regime (OF, 41.6%) and the inorganic fertilizer regime (NPK, 15.8%). Further analysis suggested that the effects of fertilization regimes were more pronounced in areas with relatively lower clay content, higher aridity index, longer experimental duration or higher soil pH. We also highlight the importance of considering local environmental factors (e.g., climate and soil conditions) in identifying appropriate fertilization regimes for maintaining soil health, mitigating greenhouse gas emissions while ensuring crop productivity. In conclusion, although NPK addition can significantly enhance SOC content, the combined application of inorganic with organic fertilizer is very important in maintaining and improving the current SOC content across China, especially in arid regions (e.g., Northwest, lower MAP regions and higher aridity index). [ABSTRACT FROM AUTHOR]

The soil organic carbon to clay ratio (SOC:clay) is a metric used in soil quality management. In Switzerland and the United Kingdom, for example, threshold values for SOC:clay ratios have been determined to indicate very good (>1:8) to degraded (<1:13) soil structures. A recent article in Soil Use and Management by Poeplau and Don, however, suggested that this metric is 'strongly biased and misleading', based on their observation that German sandy soils and heavy clay soils tend to show very high and very low SOC:clay ratios, respectively. An alternative metric was proposed based on the ratio of actual SOC to expected SOC level for a considered area. We offer a commentary on the proposal, arguing that because soil structure quality is overlooked by the approach, it fails to provide appropriate SOC levels for soil health and could lead to soils with highly depleted SOC being classified 'good'. The SOC:clay ratio, on the other hand, does address soil structure condition, providing a structure vulnerability index, a key function independent of local soil management conditions. When soils are found to have high structure vulnerability, as indicated by the SOC:clay ratio, the cropping practices at the site should be investigated and ways to increase the SOC content considered. Structure condition threshold values may only need to be reassessed if it is shown that the average structure quality observed is not in conformity with the present thresholds, which would be expected for some soils, such as Andosols. [ABSTRACT FROM AUTHOR]

The deployment of remote sensing platforms has facilitated the mapping of soil properties to a great extent. However, the accuracy of these soil property estimates is compromised by the presence of non-soil cover, which introduces interference with the acquired reflectance spectra over pixels. Therefore, current soil property estimation by remote sensing is limited to bare soil pixels, which are identified based on spectral indices of vegetation. Our study proposes a composite mapping approach to extend the soil properties mapping beyond bare soil pixels, associated with an uncertainty map. The proposed approach first classified the pixels based on their bare soil fractional cover by spectral unmixing. Then, a specific regression model was built and applied to each bare soil fractional cover class to estimate clay content. Finally, the clay content maps created for each bare soil fractional cover class were mosaicked to create a composite map of clay content estimations. A bootstrap procedure was used to estimate the standard deviation of clay content predictions per bare soil fractional cover dataset, which represented the uncertainty of estimations. This study used a hyperspectral image acquired by the Airborne Visible/Infrared Imaging Spectrometer-Next Generation (AVIRIS-NG) sensor over cultivated fields in South India. The proposed approach provided modest performances in prediction ( R v a l 2 ranging from 0.53 to 0.63) depending on the bare soil fractional cover class and showed a correct spatial pattern, regardless of the bare soil fraction classes. The model's performance was observed to increase with the adoption of higher bare soil fractional cover thresholds. The mapped area ranged from 10.4% for pixels with bare soil fractional cover >0.7 to 52.7% for pixels with bare soil fractional cover >0.3. The approach thus extended the mapped surface by 42.4%, while maintaining acceptable prediction performances. Finally, the proposed approach could be adopted to extend the mapping capability of planned and current hyperspectral satellite missions. [ABSTRACT FROM AUTHOR]

Clay is widely encountered in nature and directly influences seepage behaviors, exerting a crucial impact on engineering applications. Under low hydraulic gradients, seepage behaviors have been observed to deviate from Darcy's law, displaying a non-linear trend. However, the impacts of clay content on non-linear seepage behavior and its pore-scale mechanisms to date remain unclear. In this study, constant-head seepage experiments were conducted in sand–clay porous media under various hydraulic gradients. Low-field nuclear magnetic resonance (LF-NMR) technology was utilized to monitor the bound-water and free-water contents of sand–clay porous media under different seepage states. The results show a threshold hydraulic gradient (i0) below which there is no flow, and a critical hydraulic gradient (icr) below which the relationship between the hydraulic gradient (i) and seepage velocity (v) is non-linear. Both hydraulic gradients increased with clay content. Moreover, the transformation between bound water and free water was observed during the seepage-state evolution (no flow to pre-Darcy or pre-Darcy to Darcy). As the hydraulic gradient reached the i0, the pore water pressure gradually overcame the adsorption force of the bound-water film, reducing the thickness of the bound-water film, and causing non-linear seepage behavior. When i0 < i < icr, the enlarging hydraulic gradient triggers the thinning of bound water and enhances the fluidity of pore water. Moreover, the increasing clay content augments the bound-water content required for the seepage state's change. [ABSTRACT FROM AUTHOR]

Purpose: Soil salinity is often measured with electrical conductivity (EC) of soil–water extracts (ECw), and thus, conversion of ECw to saturated paste EC (ECe) is required for practical uses of ECw. However, conversion factors (CF, the ratio of ECe to ECw) vary widely depending on soil properties such as soil texture and ionic composition. This study was conducted to develop a novel procedure to obtain soil-specific CF by performing random forest (RF) and multiple regression (MR) modeling using EC and soil properties. Methods: Soil samples (n = 320) were collected from paddy fields in 16 reclaimed coastal areas of South Korea in 2018–2022. The samples were analyzed for EC (EC1:5 and ECe) and other soil properties including soil particle size, organic matter content, and exchangeable sodium percentage (ESP). The most important soil properties affecting the CF ratios were explored using RF modeling, and a MR equation was developed to estimate ECe using EC1:5 and the soil properties as parameters. Results: The RF model indicated that ESP and clay content are the key soil factors affecting CF variability, contributing 56.6% and 20.0% of the variability, respectively. Therefore, a multiple regression model was developed to predict CF using ESP and clay content, CF = 7.179 − 0.084 × Clay + 1.096 × ln(ESP). The predicted ECe was linearly correlated with the measured ECe (r2 = 0.84) with a marginal error (3.1%). Conclusion: Our study provides a novel method to estimate ECe from ECw by performing RF and MR modeling using soil-specific variables such as clay content and ESP. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) is a potent greenhouse gas that contributes to stratospheric ozone depletion and global climate change. Soil denitrification has two potential end-products, N2O and dinitrogen (N2), and the ratio of these end-products (N2O:(N2O+N2) or the N2O ratio) is controlled by various factors. This study aims to quantify the influence of soil pH on the ratio of denitrification end-products in Oklahoma soils with different soil textures. Six natural grassland soils encompassing three distinct soil textures were incubated in the laboratory under natural and modified pH with an overall tested pH ranging from 2 to 10. Denitrification end-products were measured in the laboratory using the acetylene inhibition technique and further estimated using a process-based biogeochemical model. Both the laboratory and model results showed that soil pH and texture influenced the ratio of the denitrification end-products. Generally, as soil pH increased the N2O ratio decreased, although both lab and model results indicated that this relationship was not linear. Soil texture may have an indirect effect on the N2O ratio, as two soils of the same texture could have different N2O ratios. However, clay percentage of the soil did show a linear positive correlation with the N2O ratio, suggesting components of soil texture may be more influential than others. Overall, soil pH was a controlling factor in the ratio of denitrification end-products and the newly observed nonlinear relationship warrants further study, particularly when considering its effects in different soil textures. [ABSTRACT FROM AUTHOR]

The presence of clay in aggregate is frequently associated with the deterioration of concrete properties. The objective of this study was to investigate the effects of varying clay contents on the mechanical properties, freeze-thaw resistance, permeability and water absorption behavior of concrete. Additionally, the differences in the permeability, and water absorption behavior of the surface layer and interior of concrete were comparatively analyzed using self-designed tests. The results indicate that the presence of a minimal quantity of clay did not diminish the compressive strength and static compressive modulus of elasticity of concrete. However, it did result in a reduction in the tensile properties and durability of concrete. Furthermore, the mechanical properties, freeze-thaw resistance, and anti-permeability of concrete were significantly diminished when the clay content reached 1.6%. Furthermore, this study proposed an innovative evaluation method for dividing the water absorption behavior of concrete into three stages, which more accurately reflected the trend of water absorption behavior in concrete. It was found that the sorptivity and permeable porosity of concrete in the three stages exhibited a strong correlation. The presence of clay increased the sorptivity and permeable porosity of concrete, with the most pronounced effect observed in the initial water absorption stage. Moreover, the permeable porosity of the interior of concrete was found to be reduced in comparison to that of the surface layer of concrete at all ages with varying clay contents, with the reduction ranging from 10.7% to 14.7%. In practical engineering construction, it is recommended that the clay content be kept within reasonable limits, and the effect of the clay content on the properties of the surface layer of concrete be given greater attention.

This study investigated the relationships between the soil organic matter content (SOM), SOM thermal pools, soil properties, and tillage practices, on cropland soils of the central plateau of Switzerland. Soil samples were collected in 45 no-till and conventional tillage fields in five layers from 0 to 40 cm depth. Soil organic carbon content (SOC) and hydrocarbon compound (HC) pools were analysed with Rock-Eval® thermal analysis. In addition, the clay content was determined by sedimentation.The SOM contents were highest in 0–5 cm of no-till soils and the plough pan of tilled soils. SOM was less oxygenated and showed lower degradation under conventional tillage then no-tillage. The proportion of the thermo-stable pool was mainly explained by the SOC:clay ratio, regardless of tillage practices. Below a SOC:clay ratio of 0.08, all pools were decreasing nearly equally with decreasing SOC. Above this ratio, thermo-stable pools increased only slightly, while thermo-labile pools increased linearly with SOC:clay on the full SOC:clay range. The 0.08 SOC:clay threshold in the thermo-stable pools content corresponded to the lower threshold of structure stability determined for Swiss and UK soils, below which, on average, severely degraded structures are observed in the field. These findings suggest that a large proportion of thermo-labile pool is necessary for acceptable to high soil structure quality, to protect the thermo-stable forms from degradation, and to reach the carbon sequestration potential of the soil.

The soil organic carbon (SOC) to clay-sized particles ratio (SOC/clay) has recently been selected as an indicator of the soil organic matter status in managed mineral soils within the framework of the European Soil Monitoring Law proposal. This indicator was initially developed to predict soil structural quality in a local study in Switzerland and was subsequently tested at national scales in England and Wales, and in Germany. In this study, we evaluated if the SOC/clay ratio was relevant to assess the structural quality of soils at the national scale in mainland France. We additionally evaluated its variant, SOC/(silt

Nitrous oxide (N2O) is a potent greenhouse gas that contributes to stratospheric ozone depletion and global climate change. Soil denitrification has two potential end-products, N2O and dinitrogen (N2), and the ratio of these end-products (N2O:(N2O+N2) or the N2O ratio) is controlled by various factors. This study aims to quantify the influence of soil pH on the ratio of denitrification end-products in Oklahoma soils with different soil textures. Six natural grassland soils encompassing three distinct soil textures were incubated in the laboratory under natural and modified pH with an overall tested pH ranging from 2 to 10. Denitrification end-products were measured in the laboratory using the acetylene inhibition technique and further estimated using a process-based biogeochemical model. Both the laboratory and model results showed that soil pH and texture influenced the ratio of the denitrification end-products. Generally, as soil pH increased the N2O ratio decreased, although both lab and model results indicated that this relationship was not linear. Soil texture may have an indirect effect on the N2O ratio, as two soils of the same texture could have different N2O ratios. However, clay percentage of the soil did show a linear positive correlation with the N2O ratio, suggesting components of soil texture may be more influential than others. Overall, soil pH was a controlling factor in the ratio of denitrification end-products and the newly observed nonlinear relationship warrants further study, particularly when considering its effects in different soil textures.

In recent decades, extensive use of nitrogen fertilizers has drastically increased ammonium contamination in soil and groundwater. Ammonium contamination in soil is governed by the adsorption mechanism, which depends on the different types of soil through which the contaminant migrates. Understanding the adsorption mechanism of ammonium (NH4+) ions and the factors influencing them is critical for predicting and mitigating contamination. This study attempted to thoroughly investigate the effects of soil clay content on adsorption and, ultimately, the retardation of NH4+ ion movement in porous media. Ammonium ion transport was investigated using soil and batch experiments for single, mixed, and layered soil types with varying clay proportions. The experimental results were validated by numerically simulating NH4+ ion migration with HYDRUS 2D software (version 2.05.0270). Furthermore, the linear superposition relationship between the distribution coefficient (Kd) and mass of each individual soil layer was investigated and found to be appropriate for calculating an integrated Kd of NH4+ ions in layered soil. The attenuation of infiltration of NH4+ ions into the groundwater was found to be greatly dependent on clay content and the orientation of the soil. Hence, this study can be immensely useful in suggesting mitigation measures to control ammonium contamination in groundwater. [ABSTRACT FROM AUTHOR]

The mechanical characteristics of the soil–structure interface have a crucial impact on the bearing capacity of offshore foundations. The thixotropy-induced strength recovery of remolded soils has a significant effect on the increase in the stability of the foundation. To explore the effects of thixotropy on the recovery characteristics of the soil–structure interfacial shear strength, a self-designed interfacial mechanical characteristic apparatus is designed in this study to perform a series of soil–structure interface tests on clays from the South China Sea and offshore Dalian, respectively. The relationship between the recovery of undrained shear strength and the change of interfacial shear strength is analyzed by the index of shear-resistant coarseness. And the effect mechanism of thixotropy on interfacial shear strength is discussed from the microscopic view. The test results indicated that the rate of increase of the soil–structure interfacial shear strength is higher than that of the undrained shear strength. The particle size index of the soil was found to significantly influence the strength recovery characteristics of the soil–structure interface. A higher clay content will accelerate the development of the interfacial shear strength. This article provides a deep insight into the thixotropic effect on the mechanical properties of the marine soil–structure interface. [ABSTRACT FROM AUTHOR]

It is extremely necessary to fully understand the mechanical properties of hydrate-bearing sediments before the commercialization of hydrate. However, few studies have explored the effect of matrix composition on mechanical behavior. In this paper, seabed clay recovered from the Shenhu Sea in the hydrate deposit area of the South China Sea and quartz sand were used as the matrix skeleton to remold hydrate-bearing clayey-sandy sediments (HBCSS). A series of triaxial tests were then carried out to investigate the effect of matrix composition (clay and fine contents) on the strength behavior of HBCSS. The results show that the fine can fill the pores and thus increase the density, which in turn enhances the strength and stiffness of HBCSS and makes the stress-strain relationship more easily softened. The lubrication of clay can significantly change the contact relationship between particles, induce strain hardening and reduce stiffness. Cohesion and internal friction angle are positively and negatively correlated with clay content, respectively. A new concept of the hardening index was proposed, which has a better quantitative description of the hardening or softening of the stress-strain relationship. The strength behavior of HBCSS is the result of the coupling of various factors. • The effects of fine and clay on the strength behavior of HBCSS are illustrated. • The influence essences of fine and clay are the filling and lubricating effects respectively. • Particle-scale shearing mechanisms are revealed. • A new hardening index is proposed to quantitatively analyze hardening or softening. [ABSTRACT FROM AUTHOR]

The creep index plays an important role in calculating the long-term settlement of natural soft clays, so it is vital to determine the creep index quickly and accurately. However, the prediction accuracy of the existing creep index models is low. This study presents seven gene expression programming (GEP) models by using different combinations of the liquid limit wL, plasticity index Ip, void ratio e and clay content CI as input variables for the prediction of creep index. A total of 151 datasets were collected from the available literature for building and testing the GEP models. The proposed GEP models were compared with two machine learning (ML) models (i.e., back propagation neural network and random forest) and five conventional empirical models in terms of three statistical indicators. The research results showed that the prediction performances of the two proposed GEP models (i.e., with combinations C I - w L - e and C I - I p - w L - e as input, respectively) surpass those of the five conventional empirical models and two ML-based models, recommended for predicting the creep index of natural soft clays in engineering practice. [ABSTRACT FROM AUTHOR]

Fine-grained silt is widely distributed in the Huanghe River Delta (HRD) in China, and the sedimentary structure is complex, meaning that the clay content in the silt is variable. The piezocone penetration test (CPTu) is the most widely approved in situ test method. It can be used to invert soil properties and interpret soil behavior. To analyse the strength properties of surface sediments in the HRD, this paper evaluated the friction angle and its inversion formula through the CPTu penetration test and monotonic simple shear test and other soil unit experiments. The evaluation showed that the empirical formula proposed by Kulhawy and Mayne had better prediction and inversion effect. The HRD silts with clay contents of 9.2%, 21.4% and 30.3% were selected as samples for the CPTu variable rate penetration test. The results show as follows. (1) The effects of the clay content on the tip resistance and the pore pressure of silt under different penetration rates were summarized. The tip resistance Qt is strongly dependent on the clay content of the silt, the Bq value of the silt tends to 0 and is not significantly affected by the change of the CPTu penetration rate. (2) Five soil behavior type classification charts and three soil behavior type indexes based on CPTu data were evaluated. The results show that the soil behavior type classification chart based on soil behavior type index ISBT, the Robertson 2010 behavior type classification chart are more suitable for the silty soil in the HRD. [ABSTRACT FROM AUTHOR]

The unsaturated permeability coefficient is of importance to study the behavior of the water seepage and contaminant transport in unsaturated soils. The direct measurement of the unsaturated permeability coefficient is time consuming and laborious. Therefore, indirect approaches are usually applied to obtain the unsaturated permeability coefficient. However, indirect methods still have some drawbacks. An indirect method is usually fitted through the soil–water characteristic curve of a special type of soil, which also requires a large workload and its application is limited. To overcome these drawbacks, a fractal model of the relative permeability coefficient of unsaturated soils has been deduced in this study based on the relation between clay contents and fractal dimensions in terms of mass. A new fractal simple prediction method of unsaturated soil absolute permeability coefficient associated with the new fractal model has also been proposed by combining the simple relation between saturated permeability coefficient and air-entry value. The method is validated with the experimental data of existing literature, and the result shows that the proposed model has a higher prediction accuracy. [ABSTRACT FROM AUTHOR]

It is particularly important to study the rheological properties and rheological behavior of liquid-phase paddy soil to improve the working efficiency of power machinery in paddy fields. In this research, a rotational rheometer was used to record the shear stress, shear rate, and apparent viscosity of the soil during the test. Additionally, a numerical model was established to explore the effects of soil clay content, moisture content, and settling time on soil rheological properties. Through single factor analysis, the contribution rate of each factor to the change in the initial apparent soil viscosity was ranked as follows: moisture content (X2) > soil clay content (X1) > settling time (X3). Subsequently, the variations in shear stress and apparent viscosity at different shear rates were explored. The changing trend of soil rheological behavior was mainly related to soil texture, in which silty loam was thixotropic and clay loam was gelatinous. The prediction models for the initial apparent viscosity were validated, and the results showed great agreement. The research evaluated and predicted the rheological behavior of liquid-phase paddy field soil and provides a reference for the design, development, and use of paddy field power machinery. [ABSTRACT FROM AUTHOR]

To further understand the characteristics of clay and sand production (hereafter collectively referred to as sand production) and to provide optimization designs of sand control schemes are critical for gas production from clayey silt natural gas hydrate reservoirs in the South China Sea. Thus, gas-water-sand production behavoirs and coupling reservoir subsidence characteristics before, during, and after hydrate dissociation of the clayey silt hydrate reservoirs with different clay contents (5%, 10%, 15%, 20%, 25%, and 30%) have been studied through a self-developed experimental system. The results show that with the increase of clay content, the total mass of sand production first increases and then decreases, and it reaches maximum when the clayey content is 20%. The sand production is the lowest before hydrate dissociation and increases significantly during hydrate dissociation, which mainly occurs in the high-speed gas and water production stage at the beginning of hydrate dissociation. After hydrate dissociation, the sand production decreases significantly. During the whole depressurization process, the clay and free sand particles generally move to the sand outlet due to the fluid driving force and overlying stress extrusion. However, for conditions of high clay contents, those particles fail to pass through the sand control screen and gradually accumulate and block the screen by forming a mud cake, which greatly reduce the permeability of the screen and limite sand production as well as gas and water production. Our research lays a foundation for sand production prediction and sand control scheme selection during gas recovery from clayey silty hydrate reservoirs that greatly need to consider a balance between sand control and gas productivity.

Near surface electromagnetic geophysical techniques are proven tools to support soil ecosystem services and soil exploration. Such geophysical techniques provide electromagnetic properties that are useful to characterize the studied soil. The link between relevant soil characteristics and geophysical properties, such as dielectric permittivity (ε), is commonly expressed by pedophysical models. However, some weaknesses remain in their application, such as the requirement of parameters that are difficult to measure or calculate. Therefore, these parameters are frequently fixed, but this oversimplifies the complexity of the investigated soils. Moreover, the validity of ε pedophysical models in the frequency range of operating soil moisture sensors (normally < 100 MHz) remains poorly investigated.In this study, the accuracy and adaptability of ε pedophysical models at different electromagnetic frequency ranges was tested and improved using newly collected laboratory and field data. Such data was collected on soils over a wide range of textures, physical and chemical properties.To achieve this, we review the measurement methods and characteristics of ε pedophysical models, soil phases and geometric parameters. Subsequently, we show how geometric parameters can explain the dependance of soil texture on ε by implementing pedotransfer functions. Then, drawing on a broad experimental basis of common soil types in Europe, we develop novel ε pedophysical models at 50 MHz. These models are not only easy to evaluate but also capture most of the soil’s complexity. Additionally, these new ε pedophysical models eliminate the need for calibration data due to the introduction of novel pedotransfer functions based on soil cation exchange capacity. An extensive model test shows an unprecedented decrease in the RMSE of the newly proposed models of up to 412%.In conclusion, despite it is unlikely to characterize soil structure, bulk density, or temperature at 50 MHz, these updated PPMs are useful for highly accurate water content and ε predictions, in both laboratory and field conditions, without the need for calibration data. As the developed modelling procedures are valid for a wide range of electromagnetic frequencies, these can be applied to soil exploration with TDR and GPR instrumentation.For reproducibility, all collected soil data are provided, alongside open-source Python code that contains the presented modelling procedures.

The spectral behavior of soil will change through degradation, which makes it difficult to retrieve soil properties using previously developed models. This study aims to use linear [including partial least squares regression (PLSR) and ratio soil index (RSI)] and nonlinear [including partial least squares-backpropagation neural network (PLS-BPNN) and partial least squares-random forest (PLS-RF)] models to estimate soil electrical conductivity (EC) and clay content in dust sources. For this purpose, 142 soil samples were collected in Khuzestan province. After laboratory spectroscopic analysis, the area and depth of diagnostic absorption features (AFs) of continuum removed (CR) spectra were calculated. The results revealed that with increasing clay content, the depth of AFs at 1400, 1900, and 2200 nm will increase. Meanwhile, an increase in the soil salinity will increase the depth and area of AFs in 1450 and 1915 nm and decrease the depth and area of AF in 2200 nm. Spectral ranges of 2100–2300 and 1400–1600 nm were identified as the most important portions of the visible and near-infrared spectrum for analyzing clay content and EC, respectively. The RSI method performed poorly in soil salinity and clay content estimation. PLSR and PLS-RF methods overestimated clay content and salinity in low values. The PLS-BPNN model had the best performance for estimating clay content (RPIQ = 4.51) and EC (RPIQ = 4.76). Considering the expected non-linear relationship between soil properties and corresponding spectral reflectance, the results of this study were acceptable. [ABSTRACT FROM AUTHOR]

Soil is a precious and non‐renewable resource that is under increasing pressure and the development of indicators to monitor its state is pivotal. Soil organic carbon (SOC) is important for key physical, chemical and biological soil properties and thus a central indicator of soil quality and soil health. The content of SOC is driven by many abiotic factors, such as texture and climate, and is therefore strongly site‐specific, which complicates, for example, the search for appropriate threshold values to differentiate healthy from less healthy soils. The SOC:clay ratio has been introduced as a normalized SOC level metric to indicate soils' structural condition, with classes ranging from degraded (<1:13) to very good (>1:8). This study applied the ratio to 2958 topsoils (0–30 cm) in the German Agricultural Soil Inventory and showed that it is not a suitable SOC level metric since strongly biased, misleading and partly insensitive to SOC changes. The proportion of soils with SOC levels classified as degraded increased exponentially with clay content, indicating the indicator's overly strong clay dependence. Thus, 94% of all Chernozems, which are known to have elevated SOC contents and a favourable soil structure, were found to have either degraded (61%) or moderate (33%) normalized SOC levels. The ratio between actual and expected SOC (SOC:SOCexp) is proposed as an easy‐to‐use alternative where expected SOC is derived from a regression between SOC and clay content. This ratio allows a simple but unbiased estimate of the clay‐normalized SOC level. The quartiles of this ratio were used to derive threshold values to divide the dataset into the classes degraded, moderate, good and very good. These classes were clearly linked to bulk volume (inverse of bulk density) as an important structural parameter, which was not the case for classes based on the SOC:clay ratio. Therefore, SOC:SOCexp and its temporal dynamic are proposed for limited areas such as regions, states or pedoclimatic zones, for example, in a soil health monitoring context; further testing is, however, recommended. [ABSTRACT FROM AUTHOR]