Increase In Clay Content Research Articles

Subsurface drainage and nitrogen management affects soil properties in upstate Missouri U.S.

Enhanced efficiency nitrogen (N) fertilizer management may reduce environmental N losses and increase grain yields. The effect of N fertilizer management practices on soil properties is uncertain. In this 5-year study, we evaluated different N fertilizer management [non-treated control (NTC), fall applied anhydrous ammonia (AA) 190 kg N ha−1 with nitrapyrin (fall AA + NI), preplant AA at 190 kg N ha−1 (spring AA), top-dressed urea (TD urea) as 42 kg N ha−1 SuperU and 126 kg N ha−1 ESN as a 25:75 % granular blend] practices in free drained (FD) and non-drained (ND) soils for their impact on soil properties. In FD soils, N fertilization significantly (P > 0.05) increased soil pH, CEC, cations, and Bray I P compared to the NTC. Improved soil aeration and increased plant growth with TD urea and spring AA fertilizer treatments in FD soils increased soil organic matter (OM) 10–13 % and total organic carbon (TOC) 27–35 % compared to the NTC. Increased clay content and reduced silt content were observed in FD soils with N fertilizer treatments compared to NTC. However, fertilizer applications in ND soils had no effect on soil properties. Increased crop production with FD and 4R N fertilizer applications can improve soil properties with increased soil OM and TOC content. This suggests that a synergetic effect of N fertilization and soil drainage can improve soil health by increasing soil cation exchange capacity (CEC), OM, and TOC content.

Particle size characteristics of sliding-zone soil and its role in landslide occurrence: a case study of the Lanniqing landslide in Southwest China

In landslide studies, particle size is a key quantitative indicator, reflecting the formation and development of the sliding zone. It plays a crucial role in understanding the mechanisms and evolutionary processes that lead to landslide occurrences. Precise measurement of particle size is crucial. This study centered on soil samples from the Lanniqing landslide in Southwest China. To begin, seven distinct methods were used to preprocess the soil samples. Next, the particle size frequency distribution was measured using the Mastersizer 2000 laser particle size analyzer. Key parameters, including median particle size, mean particle size, sorting coefficient, skewness, and kurtosis, were then compared and analyzed to determine the most appropriate preprocessing method for evaluating the characteristics of the soil samples. The mechanism of landslide occurrence was subsequently analyzed by examining the particle size characteristics, mechanical properties, and mineral composition of the soil samples. The results suggested that method C provides the most reliable analysis of particle size characteristics in soil samples. The observed coarsening of coarse particles, along with a significant increase in clay content within the sliding zone, indicates that the sliding surface has undergone multiple shear and compression events. The interplay of the upper traffic load and slope cutting at the front edge set the stage for the Lanniqing landslide, prompting the initial development of potential sliding surfaces. Rainfall acts as a catalyst for slope instability. The high clay content, combined with the formation of a low-permeability layer rich in clay minerals on the sliding surface, leads to excessive pore water pressure and mineral lubrication. These factors inherently trigger and accelerate the occurrence of the landslide.

Artificial Grassland Revegetation Improves Soil Water Retention and Storage Capacity of the Degraded Hillside Alpine Meadow

ABSTRACTThe crucial role of soil water retention and storage in soil hydrology and the water cycle is well established. However, in sensitive and degraded ecosystems like alpine meadows, the effectiveness of revegetation in enhancing these critical functions remains understudied. This study investigates the effects of revegetating severely degraded hillside meadows with artificial grasslands on soil water retention and storage capacity in the Qinghai‐Tibetan Plateau. Soil analyses at a depth of 0–20 cm revealed significant improvements in soil properties after revegetation, with increases in soil organic matter content (86.8%), total porosity (11.9%), capillary porosity (31.6%), and clay content (13.5%). Both the saturated hydraulic conductivity (Ks) and field capacity (FC) increased markedly, by 9.7% and 63.7% in the upper layer (0–10 cm) and 21.7% and 69.6% in the lower layer (10–20 cm), respectively. Structural equation modeling identified bulk density, root mass density, FC, capillary porosity, and clay content as the dominant direct factors influencing Ks with path coefficients of −0.56, 0.30, −0.53, 0.57, and −0.12, respectively, while vegetation cover and aboveground biomass were found to have indirect influences. These findings demonstrate that revegetation with artificial grasslands effectively improves soil water retention and storage capacity in degraded hillside alpine meadows by regulating key soil hydraulic and physical properties. This enhanced water‐holding capacity has significant implications for understanding the dynamics of revegetation by artificial grassland establishment in improving ecosystem health and eco‐hydrological functions in these vulnerable environments. Furthermore, the study provides valuable insights and a theoretical basis for developing ecological restoration solutions for degraded hillside meadows in other alpine regions.

Nanoscale pore structure and fractal characteristics of lacustrine shale: A case study of the Upper Cretaceous Qingshankou shales, Southern Songliao Basin, China.

The Upper Cretaceous Qingshankou Formation's lacustrine shales in the Songliao Basin are among China's most promising shale oil reservoirs. To elucidate their pore and fractal characteristics, a comprehensive set of analyses encompassing total organic carbon (TOC), X-ray diffraction (XRD), and low-temperature N2 adsorption (LTNA), Rock-Eval pyrolysis experiments and two-dimensional nuclear magnetic resonance (2D-NMR) were conducted. Using the Frenkel-Halsey-Hill (FHH) method, fractal dimensions (D) were calculated, and their relationship with pore metrics and shale compositions were explored. Two distinct fractal dimensions, D1 (0 < P/P0 < 0.5) and D2 (0.5 <P/P0 <1.0), were derived from LTNA isotherms via the FHH approach. D1 values fluctuated between 2.5715 and 2.7551 (mean 2.6564), while D2 spanned from 2.3247 to 2.4209 (mean 2.3653). Notably, D1 consistently surpassed D2, signifying that smaller pores exhibit greater homogeneity compared to their larger counterparts. D1 gradually increases with the increase of clay content. A direct correlation was observed between pore volume (PV), specific surface area (SSA), and D (both D1 and D2), whereas the association between average pore diameter (APD) and D was inverse. Both D1 and D2 escalated with diminishing TOC, 2D-NMR solid organic matter (OM), S1 content and 2D-NMR light oil. Intriguingly, D1 showed a stronger association with key pore and "sweet spot" parameters, highlighting its utility in assessing pore structural complexity and shale oil potential. This study illustrates how fractal theory enhances our understanding of pore structures and the shale oil enrichment process for the lacustrine shale.

Investigating Mechanical Characteristics of Rocks Under Freeze–Thaw Cycles Using Grain-Based Model

AbstractBased on the discrete element method (DEM), a water-contained grain-based model (GBM) is developed in this study to evaluate the effects of freeze–thaw cycles (FTCs) on the mechanical characteristics of the rock. A set of freeze–thaw and uniaxial compression tests is carried out to explore the impact of micro damage caused by FTCs on the mechanical prosperities of rock samples. By monitoring the development and distribution of micro-cracks during freeze–thaw test and uniaxial compression test, the damage mechanism of FTCs is revealed from a microscopic perspective, which shows that FTCs deteriorate the strength and brittleness parameters as exponential functions. The parametric analysis is carried out to explore the influence of porosity and mineral components on the mechanical behaviors of rock against freeze–thaw and uniaxial loadings. Based on the parametric analysis results, it is found that UCS, Young’s modulus, and total strain energy at peak stress decrease with the increase of porosity and clay content, which emphasizes the contributions of porosity and mineral components on the mechanical properties of rock samples. It is proved that the water-contained grain-based model developed in this study can capture the damage caused by FTCs on the mechanical performance of rock from a microscopic perspective, which provides novel perspectives on the phenomenon of rock degradation in response to fluctuations in temperature.

Reservoir characterization of GABO field in the niger delta basin using facies and petrophysical analyses

This study investigates the GABO field in the onshore Niger Delta Basin using well logs and core samples, with a focus on rock type distribution, reservoir continuity, and petrophysical properties to enhance hydrocarbon exploration accuracy. The research involved detailed analysis of core descriptions and images from GABO-20, along with petrophysical data from wells GABO-4, GABO-12, GABO-13, GABO-20, and GABO-51, aiming to identify rock types, evaluate reservoir quality, and determine the spatial distribution of petrophysical properties. The methodology included rigorous well log quality checks, data correlation between wells, petrophysical property evaluation, and lithofacies description. The analysis revealed thirty-five hydrocarbon-bearing zones, with GABO-20 showing average shale fraction values between 0.111 and 0.335, total porosity ranging from 0.242 to 0.329, and hydrocarbon saturation from 0.667 to 0.923, indicating substantial porosity and hydrocarbon saturation conducive to extraction. Well correlations demonstrated excellent sand-shale continuity within the reservoir intervals. Lithofacies analysis of the GABO-20 core identified eight distinct facies, including shale poles, liquid-rich shales, and sandstone poles, revealing a complex distribution of reservoir qualities with significant variations in potential. Cores 1 and 2 exhibited favourable conditions for hydrocarbon production, while Core 3 showed lower reservoir quality due to increased clay content. The depositional settings of the GABO field, particularly in the lower delta plain and delta front zones, showed well-developed reservoir bodies with moderate potential in the tidal zone and little potential in the shaly prodelta environment. This distribution highlights the complexity of the deltaic system and its implications for reservoir modeling and utilization. Reservoir zones associated with High-Quality Reservoir Facies exhibited strong petrophysical properties, suggesting excellent hydrocarbon production potential. The study underscores the importance of detailed reservoir characterization to optimize recovery strategies, offering valuable insights into the distribution and quality of reservoir sands, reducing subsurface uncertainty, and emphasizing the integration of facies and petrophysical approaches for a better understanding of reservoir characteristics in the GABO field.

A new method for reducing impurities in clay minerals

The processing of clay minerals consists, among other steps, in the removal of isolated mineral impurities, that is, not associated to crystalline structure of clay minerals, such as fractions of quartz and feldspars, originating from the process of soil formation. Thus, this work evaluated a sustainable method to reduction of isolated mineral impurities, in 4 in natura soil samples from Maranhão/Brazil, containing clay minerals. The method consisted of dispersing the samples only in water under high rotation and separating the impurities by sieving and decanting. The water and clay fraction were recovered from a manufactured solar evaporator and the clay fraction analyzed: X-ray diffraction (XRD) revealed a reduction in the intensities of mineral impurities, largely quartz, and a significant increase in the intensity corresponding to clay minerals; X-ray fluorescence (XRF) demonstrated a decrease in the SiO2/Al2O3 ratio, indicating quartz removal; Fourier transform infrared analysis (FTIR) indicated removal of organic material; thermal analysis (TG/DTG) revealed an increase in the percentage of structural water loss, suggesting an increase in clay mineral content, and adsorption/desorption isotherms of N2 demonstrated an increase in the surface areas and adsorption capacity of the benefited samples. The process yields obtained demonstrated compatibility with the particle size of the samples, with more expressive results for the more clayey ones. Thus, the investigated method, low cost and sustainable, proved to be viable and effective in obtaining clay minerals with reduced presence of isolated impurities, promoting considerable improvements in their properties, and favoring various technological applications, such as adsorption, heterogeneous catalysis, synthesis of mesoporous materials, among others.

Characterization of radon gas transmission rate in pore structures of different rock layers by radon daughters inversion calculation

Determining the transmission rate of radon gas in overburden strata is crucial for conducting a comprehensive study of radon gas's longitudinal and long-distance migration mechanisms. This study investigates the mineral components of rocks in the underground strata of the mining area using the X-ray diffraction method. Additionally, it examines the pore structure parameters of the rocks at different depths using the low-temperature nitrogen adsorption method. This research introduces an approach to inversion calculate the radon gas transmission rate through the activity ratio of radon's characteristic daughters based on the decay law and activity balance of 210Po and 210Pb daughters. In addition, it determines the transmission rates of radon gas in overlying strata at various depths through this method. The relationship between the rock's mineral composition and pore structure is investigated, and the effects of pore structure and mineral composition on the radon gas transmission rate are analyzed. The findings indicated that the pore structure exerts a dual impact on radon gas transport: macropores serve as channels for upward radon gas transport, while micropores offer most of the adsorption area. In contrast, the radon gas transmission rate is indirectly influenced by the mineral composition content associated with the medium's adsorption capacity and pore structure. In the studied lithologies, an increase in quartz content promotes radon gas transmission, while an increase in clay mineral content impedes it. Finally, the mechanisms of radon gas transport, daughter adsorption, and the impacts of rock pore structure and mineral composition on the radon transmission rate are discussed.

Experimental Study on Static and Dynamic Characteristics of Sand–Clay Mixtures with Different Mass Ratios

The alteration of soil static and dynamic characteristics induced by clay content constitutes a crucial issue in the realm of disaster prevention and mitigation within geotechnical engineering. The static and dynamic characteristics of mixed soils with varying sand–clay contents were investigated through the design and implementation of static and dynamic triaxial tests. The relationship between clay content and soil resistance to liquefaction was investigated, with an analysis of the influence of clay content on soil strength and static liquefaction performance. Furthermore, the study examined the soil’s resistance to liquefaction under dynamic constitutive and cyclic loading conditions for soils with varying clay content. Results indicate that stress–strain curves for samples with varying clay content exhibit a consistent trend, with the lowest tangent modulus and peak strength observed in samples containing 30% clay. Increasing clay content diminishes soil’s resistance to liquefaction under static loading conditions. Higher confining pressures correspond to larger tangent moduli and peak deviating stresses in triaxial shear tests. Dynamic shear modulus decreases as clay content increases, whereas damping ratio decreases accordingly. Soil gradation significantly affects liquefaction-induced deformation, with the sample containing 30% clay experiencing the fastest increase in pore water pressure during testing failure, accompanied by fewer cyclic loading cycles until failure occurs. Improving soil gradation and adjusting the sand–clay ratio are beneficial for enhancing both soil strength and its resistance to liquefaction.

Effects of low clay content on the anisotropic behavior of sand-clay mixtures: laboratory investigation using TSHCA

Undrained behavior of sandy soil with fines content is a challenge in geotechnical research. In this article, the effect of low clay content (plastic Kaolin) on the anisotropic behavior of sand is studied. In the technical literature, there are different data about the effect of fine particles (generally high percentage), but there are not enough studies on low fines content (especially plastic fines) and anisotropic conditions. For this purpose, 30 undrained tests are performed using a torsional shear hollow cylindrical apparatus (TSHCA) with constant (αo) and (b) values on Firoozkuh sand. The specimens had Kaolin contents of 0, 3, 5, 7 and 10%, and the inclination angle (αo) is varied from 15o to 60o. The specimens are prepared by dry deposition method and are consolidated under P'c= 100 and 200 kPa. The results of the experiments show that increasing the (αo) leads to more contractive behavior in sand. By adding clay particles to the host sand up to 3%, the peak strength of the specimen is increased (7% and 6% for α=15°and 30°, respectively), and then with the increase of clay content up to 10%, the strength of the specimen is decreased (33% and 22% for α=15°and 30°, respectively). But at α = 60o, with the addition of 5% clay, decrease in the peak strength is observed (about 15%) and with a further increase in the clay content, unlike the angles of 15o and 30o, increase in the peak strength of the specimen is observed, so that at 10% clay, the strength of the specimen is higher than the host sand (about 7%), which can be attributed to the cohesion nature of the clay particles. With the increase of clay content, anisotropy degree is decreased. In other words, with the increase of fines content, the anisotropic behavior is decreased.

Sedimentology and biostratigraphy of the Biancone Limestone Formation of the Tolmin Basin (Southern Alps, NW Slovenia)

The Tolmin Basin constitutes the western part of the Slovenian Basin, a large Mesozoic interplatform basin that was bounded to the north by the Julian Carbonate Platform and to the south by the Dinaric Carbonate Platform. Today, it is found along the structural boundary between the Southern Alps and the External Dinarides in northwestern Slovenia. After the drowning of the Julian Carbonate Platform, the Tolmin Basin was dominated by pelagic deposits, namely the Toarcian marlstones (Perbla Formation), the Aalenian to lower Tithonian siliceous limestones and radiolarites (Tolmin Formation), and the upper Tithonian to the Berriasian Biancone Limestone Formation. In this study, a basin-scale sedimentary evolution and calpionellid biostratigraphy of the latter is presented. The Biancone Limestone Formation is a calpionellid-bearing pelagic limestone typical of all deepened segments of the Adria microplate in this time interval. It is generally monotonous but shows considerable vertical and lateral variations. The lower boundary with radiolarites is sharp, revealing a pronounced and rapid overturn in pelagic sedimentation. The lower Berriasian slumps indicate a tectonic pulse. Rare beds of resedimented limestones, assigned to the middle Berriasian, are similar in composition to those intercalated in the underlying radiolarites. They thus show that the factors that led to a significant shift in pelagic sedimentation had little or no effect on shallow-marine carbonate production. In the upper Berriasian, an increase in clay content is evident in the formation, which is explained by the uplift and erosion of the propagating thrust belt in the Neotethys area, superimposed by humidification.

Thermal behavior (in cooling) of soil mass with varying fine and water contents: Experimental and numerical investigation

This paper presents a preliminary study on the thermal behavior and response of soil samples with varying water content to assess their significance in addressing the nighttime urban heat island (UHI) effect. For this reason, the experimental program and the analysis focus on the cooling phase of the heated soil samples. To ensure a representative analysis of field conditions, the soil samples were prepared in the laboratory with varying coarse-grained (sand) and fine-grained (kaolin) soil particles. The thermal properties of the soil samples, including thermal conductivity and transmissivity, decrease with increasing fine content and particle packing. In contrast, the thermal conductivity and transmissivity values increase with water content. The thermal diffusivity followed a similar behavior but was relatively less prominent. On the other hand, the specific heat capacity is higher in samples with higher moisture and clay contents but lower with dry unit weight. However, having a higher specific heat capacity also resulted in samples retaining the heat relatively longer and releasing it slowly, which could contribute to delayed nighttime UHI. The numerical models considering natural convective conditions and their analysis further confirm that the water content of the soil samples has a relatively more prominent effect on the soil’s specific heat capacity than the increasing clay contents. To this end, it is noted that the measurement, analysis, and estimation of heat transfer and cooling mechanisms in the soil requires careful consideration of the soil type, water content, and the surrounding environmental conditions.

Acoustic characterization of hydrate formation and decomposition in clay-bearing sediments

Understanding the acoustic characteristics of hydrates in various sediments is crucial for hydrate resource detection and safe and efficient exploitation, as hydrate occurrence patterns vary greatly in different sediments. In this work, sediments with different bentonite contents, water saturations, and types were prepared to investigate the characteristics of P-wave velocity (reflecting the magnitude of hydrate saturation in the sediment) and amplitude (reflecting the degree of hydrate-sediment cementation) during hydrate formation and depressurization. During hydrate formation, the P-wave velocity and amplitude have similar trends. As clay content increases, the P-wave velocity increase rates quickened. On the other hand, the increased rate of P-wave velocity slows down with the increase of water saturation in the clay-bearing sediments. Comparing various types of sediment shows that the water absorption and swelling of bentonite reduce the pore space, speeding up the cementation of the hydrate with the sediment and increasing P-wave velocity at a faster rate. Correspondence between P-wave velocity and hydrate saturation is strongly related to sediment type, clay content, and water saturation. The rapidly decreasing amplitude in the early stage of hydrate depressurization indicates that hydrate in clay-bearing sediments is weakly cemented to the sediments, which is prone to stratigraphic instability. The findings of this study offer guidance for hydrate resource assessments in clay-bearing sediments as well as geologic risk estimations during hydrate mining.

Effect of Modifiers on the Disintegration Characteristics of Red Clay

Due to the high degree of weathering, the red clay slope has low anti-disintegration performance, and the clay easily becomes wet and disintegrates after soaking in water. It causes geological problems such as slope collapse caused by soil softening. To study the disintegration characteristics of modified red clay, the disintegration test of red clay modified by using lignin fiber, clay particles and lime was carried out, analyzing the disintegration characteristics of improved red clay from physical and chemical perspectives and analyzing the improvement mechanism of three modifiers with the scanning electron microscopy test. The analysis results show that the water-holding capacity and disintegration resistance of soil mixed with lignin fiber decrease; the disintegration time of reshaped red clay increases with the increase in clay content; and the average disintegration rate of the soil decreases with the increase in clay content. With the increase in lime content, the soil cement increases. The integrity of the soil is enhanced, and its anti-disintegration ability is improved; the saturated moisture content of reshaped red clay increases with the increase in lignin fiber and clay content, while the saturated moisture content of soil decreases with the increase in lime content. The damage analysis shows that the larger the damage factor of soil, the worse its anti-disintegration ability, and the easier the soil disintegrates. The purpose of this paper is to explore the essence of the soil disintegration phenomenon, and on this basis, using high-quality improved materials, to improve the soil, which easily disintegrates. This move aims to significantly enhance the anti-disintegration ability of the soil, thereby improving its resistance to softening and disintegration, thereby effectively improving and maintaining the ecological environment. At the same time, the improved soil will help to improve the utilization rate of the slope and foundation soil, thereby reducing the economic cost of maintenance engineering. Against the current background of sustainable economic, social, and ecological development, it is of great strategic significance to ensure the sustainable availability of land resources in specific areas and maintain their productivity and ecological stability for a long time. The research into this subject not only helps to deepen the understanding of soil disintegration, but also provides strong technical support for the rational utilization of land resources and the protection of the ecological environment.

Machine learning-based study on the mechanical properties and embankment settlement prediction model of nickel–iron slag modified soil

Nickel–iron slag, a byproduct of industrial processes in China with an annual production exceeding 400,000 tons, is considered an industrial waste material. This study focuses on the rational utilization of nickel–iron slag by investigating its mechanical properties and road performance as a roadbed fill material. Initially, a detailed analysis of the grading curve of pure nickel–iron slag was conducted, leading to the proposal of various modification schemes for nickel–iron slag. Subsequently, static triaxial tests were performed on nickel–iron slag-clay mixtures to explore the impact of different factors on the stress–strain curve of nickel–iron slag-modified soil. Utilizing these discoveries, a formula for the molar Coulomb shear strength of nickel–iron slag-modified soil was derived. In addition, a numerical simulation study of a nickel–iron slag-reinforced embankment was conducted, integrating field tests. This aimed to investigate the variations in the compression layer sedimentation-thickness ratio and settlement factor of nickel–iron slag-modified soil reinforced embankment under different filling heights and slope rates. The results informed the development of a prediction model for the settlement ratio of nickel–iron slag-modified soil-reinforced embankment. Key findings indicate that pure nickel–iron slag exhibits poorly graded gravel sand characteristics, and optimal gradation is achieved when clay doping ranges from 30% to 40%. As the clay content increases, the stress–strain curve of nickel–iron slag-clay transitions from strain-hardening to strain-softening. Furthermore, the stress–strain curve of nickel–iron slag-cement-clay exhibits strain-softening, and the shear strength fitting formula demonstrates high computational accuracy with a small error range. Numerical simulations reveal that the sink-thickness ratio and settlement factor are minimally affected by the slope rate. The sink-thickness ratio increases with the elevation of filling height, while the settlement factor fluctuates within a small range. The proposed sink-thickness ratio prediction model exhibits high accuracy and strong generalization capabilities. This comprehensive study provides valuable insights into the efficient utilization of nickel–iron slag in construction and road engineering.

Permeability of surface clay-bearing sediments in Shenhu Area of South China Sea

The migration of fluids, such as the dissociation of natural gas hydrates, can affect the stability of the seabed and even induce submarine geological disasters and change the marine environment. The migration of fluids in sediments depends on its permeability properties. Therefore, it is crucial to investigate the sediment permeability and its influencing factors. This paper investigates the particle size, porosity, pore size distribution, and permeability of surface clay-bearing sediments in the Shenhu Area of the South China Sea by physical property tests, computed tomography (CT) scanning tests, constant rate of strain (CRS) consolidation tests, and nuclear magnetic resonance (NMR) tests. The permeability of the surface sediments in the Shenhu Area ranges from 3.32 × 10−15–6.76 × 10−14 m2. The pore size mainly ranges between 10−5 and 10−1 mm, exhibiting a bimodal distribution with peaks from 10−4 and 10−2 mm. The increase in clay content leads to enhanced permeability due to the bimodal distribution of pore sizes, which will cause the enlargement of pores. As the pore size increases, the sediment permeability also increases. Sediment permeability linearly decreases with increasing effective axial stress and deformation due to compression of the pore space. Additionally, a new model for calculating permeability with different sediment properties is established, which improves the accuracy of permeability calculations for clay-bearing sediments compared to previous research. The findings of our study can provide a reference for exploring the influence of sediment parameters on fluid migration mechanisms in clay-bearing sediments.

Spatio-temporal characterisation of local scour around a circular bridge pier in cohesive soil with different clay/silt ratio

This paper presents new data on scour around a vertical pier in cohesive soils. It specifically focuses on the temporal evolution of local scour hole around the pier with increasing the clay/silt ratio content. Series of flume tests were performed using soil mixtures made with 85% fine sand and 15% fines. The fines fraction used in the soil mixtures includes silt, kaolinite clay, and various combinations of both with different proportions. The water velocity during the tests was kept constant and slightly above the erosion critical velocity of the fine sand used in the mixtures. A 3D laser scanner was employed to continuously record the geometry of the scour hole. Results show that increasing the Kaolinite clay in the fine fraction reduces significantly the scour. The mixture with a range around 7.5–10% of kaolinite clay fines content provides the threshold composition for cohesive soil behaviour effect in scouring process, recognized through scour pattern change. As the clay content increases, notable reductions are observed in the dimensions of the scour hole. Furthermore, the temporal evolution of maximum scour depth measured in flume was in agreement with the results from SRICOS-EFA (Scour Rate in COhesive Soil - Erosion Function Apparatus) method.

Biocrusts affect preferential flow and water holding capacity by regulating soil properties in Ultisols from subtropical China

Biological soil crusts (BSCs) play an important role in regulating the process of soil infiltration, and thus changing soil hydrological processes. However, little attention was paid to the effects of BSCs on soil infiltration and water holding capacity in the humid region. Therefore, the objective of this study was to quantitatively characterize the flow pathways of BSCs on soils developed over Quaternary clay and muddy shale from subtropical China by using dye tracer experiments. To determine the effects of BSCs on soil water holding capacity, the soil water characteristic curve (SWCC) was also measured. Results showed that BSCs significantly reduced the soil water infiltration compared with the bare soil. The dyeing coverage (DC) of BSCs on Quaternary clay and muddy shale decreased by 8.4% and 1.8%, respectively. SWCC results showed that the water content of BSCs was 3.5%–42.8% higher than that of bare soil under the same matrix potential, indicating that BSCs increased the water holding capacity. BSCs affected preferential infiltration by regulating surface soil properties, such as increased soil organic matter content (SOM), silt and clay content, and decreased bulk density (BD) and sand content. Furthermore, PLS-PM results revealed that BSCs and its induced increase of silt and clay content played important roles in inhibiting preferential infiltration. The results could help us to better understand the effects of BSCs on soil hydrological processes in Ultisols from subtropical China.

Evaluation of the effect of the mixture of soil textural compounds on the strength of the soil crust: Coding and optimization

Soil is one of the most important parts of an ecosystem. If soil particles are conserved in a basin, it will be possible for the ecosystem to survive. In this study, clay, silt and sand particles were selected as soil conservation compounds and strength and wind erosion tests were performed to assess the crust strength of these compounds. Moreover, due to the lack of clear relationships between these parameters, this research aims to identify the correlations among them. These particles were coded at specific intervals in terms of application rate and then used as inputs in Design Expert software. After 48 h, a penetrometer test was performed on crust layers. The results showed that based on significant correlations between the simulation and laboratory data, the best models are the 2FI mathematical model (strength test) and quadratic (wind erosion). The simulation results indicate that the values of R2 and Adj-R2 were 0.8994 and 0.9311 respectively, and the signal-to-noise ratio was 21.254. The interaction effect of the treatments showed that application of clay in the studied compounds increased penetration strength of the layer. Also, with the increase in clay content, wind erosion first increased and then decreased, and this trend is directly related to the characteristics of clay. Further, the accuracy of the wind erosion simulation results was R2 = 0.9561. According to the optimization results, the maximum soil resistance occurred with 15 g each of clay, silt, and sand. However, it remained constant when sand content increased. This study suggests that application of each compound creates a very different behavior in the formation of soil crust that can be used in many projects on a local and global scale.

Development of 3D printable stabilized earth-based construction materials using excavated soil: Evaluation of fresh and hardened properties

Soil excavated during construction and demolition can be utilized to reduce the demand for natural sand in 3D printed constructions. This research attempts to systematically develop 3D printable stabilized earth-based materials using excavated soil (clay content of 42.5 %) as 25 % and 50 % replacement of natural sand, and examine their compressive strength, water permeable porosity, and moisture sensitivity. The effectiveness of two binder systems – Ordinary Portland Cement (OPC) and a combination of OPC and ground granulated blast furnace slag (GGBS used to replace 30 % OPC by mass), was investigated. Non-expansive clay in the soil leads to a steeper reduction in apparent viscosity, 12–15 % higher flow retention, and 50–60 % lower plastic viscosity of soil-based mixes, thus contributing to superior extrusion quality at 35–40 mm lower initial flow than OPC-sand and OPC-GGBS-sand mixes. The addition of GGBS, due to its irregular particle morphologies and interlocking effects, further enhances the shape retention of the printed layers by 8–26 % compared to OPC-soil mortars. The structural build-ups in OPC-soil and OPC-GGBS-soil mortars increase with the increase in clay content, which enabled buildability up to a height of 1.2 m compared to only 0.51–0.55 m for OPC-sand and OPC-GGBS-sand mortars. Higher water demand due to the addition of natural clay increases the porosity of 3D printed OPC-soil mortars, thereby lowering compressive strength and increasing moisture sensitivity. However, a blend of OPC and GGBS substantially reduces the moisture sensitivity of the printed mortars at 28-day age, attributed to better stabilization of clay through hydraulic and pozzolanic action of GGBS. 28-day wet compressive strength of 14–25 MPa is obtained for the printed soil-based mixes depending on the soil dosage and loading direction. In summary, the study provides a feasible solution for the 3D printing of stabilized earth structures with lower demand for natural sand and OPC.