Fine Soil Particles Research Articles

THE EFFECTS OF WATER CONTENT AND GRAIN SIZE ON THE CLOGGING AND ABRASIVITY OF FINE-GRAINED SOILS IN MECHANIZED EXCAVATION

Clogging during excavation is one of the common problems in mechanized excavation. Among the influential factors in clogging of the cutter head, we can mention the percentage of fine soil particles (under 200 mesh sieve), soil moisture, and soil type. In this study, to investigate the mechanism of tunnel excavation in the laboratory, a tunnel excavation machine laboratory simulator was designed and built. The features of this device are its horizontal operation, the low rotation speed of the cutter head, continuous contact of the pins with fresh soil during the test, and the continuous injection of additives with a specific injection pressure during the test. The effect of the percentage of fine-grained, soil moisture and the foam injection ratio (FIR) on clogging, energy consumed, and the average wear of cutting tools was studied. The results showed that with an increase in the percentage of fine soil particles from 90 to 100%, the clogging of cutting tools increased by 50%. Also, with an increase of soil moisture from a dry state to moisture content of 5%, clogging of the cutter head is insignificant, and after that, with an increase of moisture from 10 to 25%, clogging is increased by 178%, and the amount of energy consumed in each test is increased by 84%. In addition, by increasing the foam injection ratio from 40 to 60%, clogging decreased by 81% on average, and the wear of cutting tools decreased by 62% on average.

Frost heave mitigation of silt clay using nonionic polyacrylamide

Frost heave occurs frequently in high-latitude or high-altitude areas in many parts of the world, and it is a common challenge for geotechnical engineers in road construction. In order to solve the excessive frost heave induced frost damage to geotechnical engineering in cold regions, frost heave susceptible soil from the Tibetan Plateau (the seasonal frozen area) is modified by nonionic polyacrylamide (NPAM) and then used for frost heave testing. Moreover, cohesion test, permeability test, scanning electron microscopy (SEM) test, and Fourier transform infrared spectroscopy (FTIR) analysis are carried out on the NPAM modified soil to gain more insight into the frost heave mitigation mechanism. The impact of NPAM on soil frost heave and its physicochemical mechanism for frost heave mitigation are subsequently investigated. Our results demonstrate that NPAM is physically adsorbed on the surface of soil particles through hydrogen bonding. The increase of NPAM content does not only increase the viscosity of the solution, but it also enhances the aggregation of fine soil particles. In addition, the permeability of the modified soil decreases with increasing NPAM content, thus implying an increase in the water migration resistance. NPAM can be effectively used to reduce the frost heave susceptibility of soil. Our results show that 0.3 wt% of NPAM can significantly convert a strong frost heave soil to a weak frost heave soil. Our results reveal the mechanism of frost heave mitigation using NPAM and provides engineers and researchers with a new physicochemical method for the treatment of frost heave susceptible soil in railway and road construction in cold regions.

Fine soil particle aggregation in ultra-fine bubble irrigated paddy fields

Abstract The flotation method of ultra-fine bubbles (UFB) aims to address pollution and has been used for combating the undesirable water conditions of contaminated soils. Hence, water containing UFB is gaining increasing attention for potential agricultural applications. Although certain hypotheses have been proposed, such as the collection of ions in water through the electrical characteristic of UFB, no clear experimental data have been provided. We found that improvement in turbidity may cause the adsorption of fine soil particles in the water by the UFB, thereby improving the quality of the water. The data from the paddy field showed that a decrease in turbidity (below 2 nephelometric turbidity units) occurred over a short period of time (3 days). UFB concentration is directly related to turbidity with a coefficient of determination of 0.93. This phenomenon was also observed through the distribution of bubbles and soil particles, where the average particle size increased because of the aggregation of soil particles and the decrease in turbidity in the paddy field, indicating that UFB collect soil particles and thereby improve water quality. Therefore, UFB are highly effective in cleaning rice field water and will be a preferred method for purifying the environment in the future.

Effects of Different Hedgerow Patterns on the Soil Physicochemical Properties, Erodibility, and Fractal Characteristics of Slope Farmland in the Miyun Reservoir Area.

Soil erosion of sloping farmland in the Miyun reservoir area in Beijing has become a serious issue and has threatened the ecological environment and safety of the reservoir area. We used the Taishizhuang Village Non-point Source Pollution Prevention & Control Base in the Miyun reservoir as a study area and performed a comparative analysis of the physicochemical properties of soil of the upper, middle, and lower slopes of the Scutellaria baicalensis + Buchloe dactyloides plot (Treatment 1, T1), Morus alba + Buchloe dactyloides plot (Treatment 2, T2), Salvia miltiorrhiza + Cynodon dactylon plot (Treatment 3, T3), Platycodon grandiflorus + Cynodon dactylon plot (T4), and a barren land control plot (Control check, CK), to explore how different hedgerow patterns affect the soil’s physicochemical properties, anti-erodibility, and fractal characteristics. We found the following: (1) The primary soil mechanical composition included sand particles in the upper slopes, whereas it was soil fine particles in the middle and lower slopes. (2) The fractal dimension of the slope soil showed a significant negative correlation with sand particles (R2 = 0.9791) while being positively correlated with silt particles (R2 = 0.9635) and clay particles (R2 = 0.9408). (3) All hedgerow patterns increased soil nutrients, with the Morus alba + Buchloe dactyloides hedgerow plot increasing the soil total nitrogen (STN), soil total phosphorus (STP), and soil organic matter (SOM) content by 213.89–282.69%, 55.56–58.15%, and 29.77–56.04%, respectively. (4) The Morus alba + Buchloe dactyloides hedgerow plot significantly decreased the soil erodibility factor K value, improved soil anti-erodibility, and reduced soil erosion. (5) The K value of the soil erodibility was significantly negatively correlated with clay particles, soil fractal dimension, and STP (p < 0.01); positively correlated with sand particles; and negatively correlated with silt particles, STN, and SOM. Therefore, the Morus alba + Buchloe dactyloides hedgerow planting contributes to clay particle conservation, soil nutrient content improvement, soil structure optimization, and soil anti-erodibility enhancement.

Bioaccessibility of Pb in health-related size fractions of contaminated soils amended with phosphate

Lead (Pb) contamination is one of the most significant exposure hazards to human health. Contaminated soil particles may be eroded and transferred either to the atmosphere (<10 μm) or to streams; or they may be incidentally ingested (<200 μm). Among strategies for the long-term management of this risk, one of the most cost-effective is the reduction of Pb mobility and bioavailability via amendment with phosphorus-containing materials.To clarify the effectiveness of P amendment in reducing Pb mobility and bioaccessibility in different soil size fractions, an experiment was performed by adding a soluble P compound to a historically contaminated urban soil (RO), a mining soil (MI), and an uncontaminated spiked soil (SP) at different P:Pb molar ratios (2.5:1, 5:1, and 15:1).In the <10 μm fraction of soils, P addition reduced bioaccessible Pb only in the SP soil at the highest dose, with little to no effect on RO and MI soils. Similarly, in the coarse fraction, Pb was immobilized only in the SP soil with all three P doses. These results were probably due to the higher stability of Pb in historically contaminated soils, where Pb dissolution is the limiting factor to the formation of insoluble Pb compounds.The bioaccessible proportion of Pb (using SBET method) was higher than 70 % of the total Pb in all soils and was similar in both fine and coarse particle fractions. Due to the enrichment of Pb in finer particles, this implies possible adverse effects to the environment or to human health if these particles escape from the soil. These results call for increasing attention to the effect of remediation activities on fine soil particles, considering their significant environmental role especially in urban and in historically low or moderately contaminated areas.

Spatiotemporal characteristics of arsenic and lead with seasonal freeze-thaw cycles in the source area of the Yellow River Tibet Plateau, China

Study regionThe source region of the Yellow River, China (SAYR) Study focusThis study focuses on demonstrating the impact of seasonal freeze-thaw process on the seasonally arsenic (As) and lead (Pb) concentration in the water bodies, such as river, lake, and spring. 113 surface water samples in April (freeze permafrost), 164 in July (active layer in permafrost thawed), and 86 soil samples at various depths in July were collected. Statistical correlation and principle analysis were applied to find the connection between tracer metals in water bodies and the various environmental factors. The percentage of soil particle size (5–50 µm), which can reflect the intensity of the freeze-thaw process in the permafrost soil, influenced the soil and water As and Pb trace metal concentrations differently in the permafrost area. New hydrological insights for the regionIn April, the average As concentrations were 23.4 ± 16.7, 39.4 ± 32.6, 26.5 ± 24.4 μg/L, respectively in river, lake and spring water samples, and Pb concentrations were 34.9 ± 27.1, 47.4 ± 38 and 48.9 ± 33.4 μg/L. While the As concentrations in waters in July all decreased by 2 or 3 times compared with those in April, Pb concentrations slightly increased. Permafrost thawing enhanced the weathering of As and Pb, but the high As adsorption on fine soil particles, resulting from the seasonal freeze-thaw cycles, leaded to the significant decrease in the water As concentration in July, in addition to the rainfall dilution. The slight increase in Pb water concentration in July suggesting the effects of enhanced weathering and dilution were equally important. The higher As and Pb concentrations around the large Gyaring and Ngoring lakes than other SAYR area, shaping the spatial distribution of As and Pb, might be due to evaporative enrichment and the high phosphate content in the lakes. Results are helpful in assessing the ecological impact of trace metals in the permafrost area with climate change.

Evaluating Spatial-Temporal Clogging Evolution in a Meso-Scale Lysimeter

When surface water infiltrates soil, the fine soil particles carried in water gradually clog soil pores and form a low-permeability soil layer. Clogging impacts the variations in pore water pressure heads in soil and effective hydraulic conductivity. However, few studies have connected field measurements of pore water pressure heads to clogging in soil. This study proposed a diagram to demonstrate the relationship between the normalized pore water pressure head (λ) and effective hydraulic conductivity (Keff) based on a conceptual 1-D vertical infiltration model. The coevolution of λ and Keff indicated the occurrence of clogging and its location relative to the pore-pressure measurement point. We validated the λ-Keff diagram based on a series of numerical simulations of infiltration experiments in a lysimeter. The simulation results showed that the proposed diagram not only indicated the occurrence of clogging but also the development of the unsaturated zone beneath the upper clogging layer. Furthermore, we used a diagram to analyze the spatiotemporal changes in permeability in a lysimeter during three cycles of physical infiltration experiments. The experimental data presented with λ-Keff diagram indicated cracking on the soil surface, and clogging gradually developed at the bottom of the lysimeter.

Coupled effect of porous network and water content on the natural attenuation of diesel in unsaturated soils.

The natural attenuation potential of a vadose zone against diesel is critical for optimizing remedial actions and determining groundwater vulnerability to contamination. Here, diesel attenuation in unsaturated soils was systematically examined to develop a qualitative relationship between physical soil properties and the natural attenuation capacity of a vadose zone against diesel. The uniformity coefficient (Cu) and water saturation (Sw, %) were considered as the proxies reflecting the degree of effects by porous network and water content in different soils, respectively. These, in turn, are related to the primary diesel attenuation mechanisms of volatilization and biodegradation. The volatilization of diesel was inversely proportional to Cu and Sw, which could be attributed to effective pore channels facilitating gas transport. Conversely, biodegradation was highly proportional to Cu under unsaturated conditions (Sw=35-71%), owing to nutrients typically associated with fine soil particles. The microbial community in unsaturated soils was affected by Sw rather than Cu. The overall diesel attenuation including volatilization and biodegradation was optimized at Sw=35% for all tested soils.

Critical hydraulic gradient and fine particle migration of sand under upward seepage flow

In order to study the mechanism of seepage-induced geotechnical damage and characteristics of fine particle migration in sandy soil, a one-dimensional upward seepage test device was used and a series of upward seepage flow tests of sand were conducted. In these experiments, the permeability, fine particle migration and redistribution under different hydraulic gradients were investigated. The results show that local hydraulic gradient in the sand sample is larger than the critical hydraulic gradient calculated by the Terzaghi’s Equation. The seepage force will induce the fine soil particles to migrate along water flow direction and then cause the redistribution and reconsolidation of sand particles. Under the test condition, fine particles (< 0.075 mm) and fine sand particles (0.075–0.25 mm) dominate in the lost soil particles. Soil particles larger than 0.6 mm are hardly to lose.

Checkerboard Barriers Attenuate Soil Particle Loss and Promote Nutrient Contents of Soil

In the arid and semi-arid regions of the world, checkerboard barriers play a vital role in ecological restoration. However, the improvement of soil quality in the later stages of lattice barrier-laying is an issue that is not yet known. This study selected dunes lined with Salix psammophila (SL) and high-density polyethylene (HDPE) checkerboard barriers in the desert zone of an arid zone, and no-barrier dunes were used as the control area. We assessed the soil properties of different dunes’ windward slopes using a combination of particle size characteristics and soil nutrients and using soil nutrients to build a soil quality index (SQI). The laying of checkerboard barriers has a positive effect on the accumulation of fine soil particles and the improvement of soil quality. It ultimately leads to an increase in fractal dimension in the 0–2 cm and 2–4 cm soil layers. SQI and soil nutrients show consistent trends. The SQI of the different dune types follows the order: SL (0.22) &gt; HDPE (0.14) &gt; CK (0.12). We also found an interaction between soil nutrients and particle characteristics through statistical analysis. With a comprehensive assessment of checkerboard barriers installed on dunes, SL can provide better soil restoration benefits.

Shear rate effect on the residual strength of saturated clayey and granular soils under low- to high-rate continuous shearing

The residual strength of sliding basal soils plays a pivotal role not only in the movement of bedding landslides controlled by clay-rich interlayers but also in remobilized granular deposits. Many studies have focused on better understanding the residual shear behaviors of clayey and granular soils under relatively low shear rates. However, the residual strength varies with various clay fractions for clayey soils and fine-size fractions for granular soils, as well as shear rates (especially in fast ranges) need further examined. In the present research, results of a low- to high-rate continuous ring shear test on a clayey soil and three granular soils at the shear rates ranging from 0.5 to 50.0 mm/s were reported. The clayey soil was remolded from the shear zone soil of a bedding landslide controlled by a clay-rich interlayer with main minerals of illite-smectite, and the granular soils included two silica sands and one mixture of silica sand with fine granite residual soil particles. The results show that saturated clayey soil has an obvious positive shear rate effect on its residual strength after a certain shear rate; the mechanism is the transformation of shear mode, i.e., from sliding shearing to turbulent shearing with the increasing of shear rate. The high clay fraction may promote this transformation of shear mode. In addition, the critical shear rate of the clayey soil that has a positive shear rate dependency of the residual strength (i.e., rate-strengthening) is related to the clay fraction, i.e., a smaller critical shear rate appears in the clayey soil with higher clay fraction. The residual strength of saturated granular soils with different fine-size fractions do not show any shear rate-dependent, while the fine-size fraction affects the residual strength both in drained and undrained conditions; that is, the higher the fine-size fraction is, the lower the residual strength is. Moreover, the neutral shear rate effect of granular soils in this study may be related to the low normal stress and low shear rate range. The authors believe that, results such as those obtained in this work, may be useful for developing a more suitable constitutive model to better understand the postfailure motion (or reactivation kinematics) of bedding landslides controlled by clay-rich interlayers, as well as rock avalanche deposits remobilized by heavy rainfall.

Simultaneous removal of suspended fine soil particles, strontium and cesium from soil washing effluent using inorganic flocculants

The purpose of this study was to remove suspended soil, Sr 2 + , and Cs + that may exist in soil-washing effluents using an inorganic coagulant (J-AF). The major chemical constituents of the flocculant J-AF were SO 3 and CaO, and were confirmed to have thenardite (Na 2 SO 4 ), calcium carbonate (CaCO 3 ), and tychite (Na 6 Mg 2 (CO 3 ) 4 (SO 4 )) crystals. When 10 g/L of J-AF was injected into the turbid solution containing unstably suspended soil particles of < 45 μ m , the suspended soil could be completely precipitated. The agglomerates of suspended soil formed using J-AF had a maximum size of more than 1 mm, due to which sedimentation was effective. The precipitation of suspended soil by J-AF was more favorable under acidic conditions, such as pH 2, 3, and 5. Sr 2 + was mainly removed from the supernatant by adsorption using J-AF, and Cs + was precipitated by J-AF while adsorbed on suspended soil and subsequently eliminated from the supernatant. These results provide that J-AF can be used for the simultaneous removal of suspended soil, Sr 2 + , and Cs + from a radioactive soil suspension. • J-AF successfully flocculated and precipitated suspended soil. • Suspended soil precipitated favorably at pH 2, 3, and 5. • Sr 2+ was adsorbed by soil and J-AF, and was partially co-precipitated. • Cs + precipitated while adsorbed onto the soil and separated from the aqueous phase.

Long-Term Field and Horticultural Crops Intensification in Semiarid Regions Influence the Soil Physiobiochemical Properties and Nutrients Status

The study was conducted to assess the long-term effects of predominant land uses on physicochemical properties, nutrient status and their interactions in soils of south-western Punjab representing the semi-arid soils of India. From each site, soil samples of three predominant land use viz. croplands, horticultural lands and uncultivated lands were collected from 0–15, 15–30, 30–60 and 60–90 cm depths. Soils of both croplands and horticultural lands were classified as sandy loam whereas uncultivated lands showed loamy sand texture with relatively higher pH, electrical conductivity (EC) and bulk density (Bd). Greater soil organic carbon (SOC), available nitrogen (N), phosphorus (P) and micronutrients (Zn, Cu, Fe and Mn) in horticulture might be due to the higher addition of OC and mineral nutrients through the decomposition of leaf litterfall and root deposits over their removal from soils while long-term use of potassic fertilizer raised the available K contents in croplands. Profile study up to 90 cm depicted the largest sequestration of 74.89 Mg C ha−1 under orchards which was 40 and 70% higher than croplands and uncultivated lands respectively. Significant variability in water-stable aggregates (WSA) (R2 = 0.5843, p &lt; 0.05) and mean weighted diameter (MWD) (R2 = 0.6497, p &lt; 0.01) with SOC indicated better soil stability in horticulture due to the presence of higher SOC. Positive relations of soil available micronutrients with SOC and finer soil particles were supported by the results of correlation, Principal component analysis and dendrogram indicating horticulture as a potent source of available micronutrients. An overall superiority of horticultural land use over the other two land uses in terms of nutrient status and soil stability suggests its inclusion as a positive strategy that could be taken into account in policymaking for maintaining productivity along with the sustainability of the concerned land degradation prone area.

Grassland restoration on former arable land: Fine‐scale grass accumulation and damaged soil conditions limit species establishment

AbstractQuestionWhich vegetation and soil parameters limit species establishment in restored grasslands? Do these parameters operate predominantly on a fine or a community scale?LocationWhite Carpathian Mountains, SE Czech Republic.MethodsWe compared 16 grasslands restored on former arable land with 9 well‐preserved reference grasslands. We sampled cover of plant species in plots of 2 m × 2 m (community scale) in which four 20 cm × 20 cm subplots (fine scale) were nested. We quantified fine‐scale heterogeneity as the mean Sørensen dissimilarity index among the species composition of the subplots. To characterize site conditions, we analyzed soil properties, above‐ground plant biomass and its nutrient content.ResultsRestored grasslands had a lower number of plant species at both the community and fine scales. Species number at the community scale was positively associated with the species number at the fine scale (irrespective of grassland type), but was not associated with fine‐scale heterogeneity. This indicates the importance of fine‐scale biotic interactions for overall species diversity. In support of this, in both grassland types, the species number was negatively associated with the cover of grasses, but only at the fine scale. Total cover (but not the biomass) was lower in restored grasslands, and was positively related with species number, particularly in restored grasslands. This indicates that the lower species number in the restored grasslands mainly resulted from deteriorated abiotic conditions. Such deterioration of the plant environment can be attributed particularly to the soil of the restored, formerly plowed grasslands. They had a lower soil organic matter content and a higher proportion of fine soil particles (silt and clay), indicating reduced soil water availability. The lower soil N content of restored grasslands was also reflected in the nutrient content of plant biomass, where lower N:P and N:K ratios indicated a limitation of plant growth by N‐supply.ConclusionThe species number was generally driven by fine‐scale biotic interactions, which operated similarly in both grassland types. The reduced number of plant species in restored grasslands is the result of several factors among which altered soil conditions in the former arable land appears to be highly important.

On the Dynamic Mechanical Behaviors of a Fault Unwelded Bimrock Exposed to Freeze-Thaw-Fatigue Loads: A Lab-Scale Testing

This work is aimed at investigating the mechanical behaviors of a fault unwelded bimrock subjected to coupled freeze-thaw (FT) and fatigue loads. The influence of FT cycle on rock strength, deformation, damage evolution, and failure morphology was detailed investigated. The testing results show that the soil-rock interface is sensitive to freeze-thaw condition. Interface damage and cracking contribute a lot to sample strength, volumetric deformation, and damage evolution. In addition, a sudden increase of stress amplitude results in the increase of damage, afterwards, the coupling degree of bimrock improves with the increase of loading cycles. A coupling freeze-thaw and mechanical damage evolution model was proposed using the damage index defined by ultrasonic velocity and axial strain. It is found that the evolution trend of the model is strongly related to the previous freeze-thaw damage. Moreover, failure mode of bimrock changes from shear failure to bulging failure with increasing FT cycles. The failure process of bimrock is the rearrangement of the fine soil particles and rock blocks, the soil matrix and rock block bear axial cyclic loads by their interactions.

Prediction Method for Fine Particle Loss Rate of Sandy Soil under Suffusion

In the process of seepage, the internally unstable fine particles of sandy soil are easy to be lost and form suffusion, which has a negative effect on the geotechnical building or foundation. The loss rate of fine particles is a key parameter for soil mechanical property degradation and stability analysis. In order to predict the loss rate of fine particles in sandy soil under suffusion, the internal stability evaluation criteria for determining whether soil will undergo suffusion is discussed first. Second this paper gives critical hydraulic gradient for erosion initiation and introduces the stress reduction factor. And then considering the difference of soil particles' forces, the stress reduction factor is modified, meanwhile the “erosion initiation probability of fine particles” is introduced to quantify the erosion initiation of fine particles. Next the migration process of fine particles in the pore network of soil is analyzed, and the probability of fine particles through constriction and the migration distance are given. Finally, the law of fine particle erosion and deposition are given according to the law of fine particle erosion initiation and migration, and the prediction method of fine particle loss rate was formed based on the law of mass conservation. The calculated results of fine particle loss by this prediction method are in good agreement with the numerical results, and the error is basically within 15%.

Thermal desorption behavior of fluoroquinolones in contaminated soil of livestock and poultry breeding

As a kind of typical veterinary drug, fluoroquinolone antibiotics (FQs) are widely used in the field of livestock and poultry breeding, but these FQs escape to surrounding soil through various pathways, polluting soil through long-term accumulation. Current study proposed a clean technology named thermal desorption to deal with FQs contaminated soils. It was observed that time, temperature and soil particle size were the critical factors in FQs thermal desorption. Results of the study showed that higher temperature was more effective in the removal of FQs, while removal of FQs attached with finer particles was more difficult compared to coarse particles. Fine soil particles (0.6–0.85 mm) were decontaminated up 99.4% when treated with 400 °C for 60min. Thermal desorption of FQs from contaminated soil was governed by first-order kinetics. Based on the detection of exhaust gas components, a possible thermal desorption mechanism was proposed. Study suggested that thermal desorption was a clean and effective remediation method to treat FQs-contaminated soils without generating any further waste.

Experimental study of the dynamic characteristics of Songhua River silt with fine grains under freeze-thaw cycles using asymmetric hysteresis

The contact and bonding of soil particles are affected by the fine particle content of silty sand and the freeze-thaw cycle effects in the seasonal frozen zone, which are reflected as the dynamic characteristics of silty sand from the macroscopic point of view. The dynamic stress, dynamic shear modulus, dynamic shear modulus ratio, and damping ratio of Songhua River silt with different contents of fine soil particle (less than 0.075 mm) after repeated freeze-thaw cycles were studied respectively using a low-temperature dynamic triaxial test system and were compared with those of quartz sand. In order to approach the real test results, a piecewise equation was used to solve for the dynamic parameters. The results show that repeated freeze-thaw cycles have a great influence on reducing the dynamic stress, the dynamic shear modulus, and the dynamic shear modulus ratio, while they increase the damping ratio. For a given fine particle content and number of freeze-thaw cycles, the dynamic stress, dynamic shear modulus, and damping ratio of the Songhua River silt with fine particles are larger than those of quartz sand when the dynamic strain reaches 0.2%, and the difference gradually decreases as the number of freeze-thaw cycles increases. The dynamic shear modulus of the Songhua River silt with fine grains decreases more slowly with increasing dynamic strain than that of quartz sand. Therefore, a normalized empirical model was established to describe the relationship between the dynamic shear modulus ratio, the damping ratio, and the dynamic strain. This model is suitable for Songhua River silt with different fine particle contents and numbers of freeze-thaw cycles, and it provides good prediction results. Furthermore, the evolution of the model parameters with the experimental conditions was analyzed, and the limit value of the fine particle content was determined to be 10%. After repeated freezing and thawing, the influence of the fine particle content on parameters a and c weakened. The regression relationship between the model parameters and the test conditions can be described by a binary quadratic equation. It is suggested that the soil parameters should be used for the dynamic response analysis of Songhua River silt with fine grains after five freeze-thaw cycles.

Tracing hotspots of soil erosion in high mountain environments: how forensic science based on plant eDNA can lead the way. An opinion

High mountain environments are among the most fragile on Earth. Due to anthropogenic disturbances and the exposure to extreme weather events, the rates of soil erosion have recently been accelerating, resulting in ecological degradation and geological hazards. Ecological restoration of mountains and an improved understanding of nature-based solutions to mitigate land degradation is therefore of utmost urgency. Identifying hotspots of soil erosion is a first step towards improving mitigation strategies. A promising methodology to identify erosion hotspots is sediment source fingerprinting, that differentiates the properties of soil from different sources, using signatures such as elemental geochemistry or radionuclides. However, in areas with complex lithologies or shallow and poorly developed soils, geochemical fingerprints allow only a rough distinction between erosion hotspots. In this opinion paper, we explore the relevance of environmental DNA (eDNA) that originates from plant litter and fixes onto fine soil particles, as a targeted sediment fingerprinting method sensitive to vegetation that could potentially allow the identification of erosion hotspots and their relative importance from sedimentary deposits. Pioneering studies indicate that eDNA allows not only the detection of specific vegetation communities, but also the identification of individual plant species. Supported by the increasing availability and quality of vegetation maps and eDNA reference libraries, we argue that sediment source fingerprinting using eDNA from plant litter, will evolve into a valuable method to identify hotspots of soil erosion and allow stakeholders to prioritize areas where ecological restoration is necessary in high mountain environments.

Wind Tunnel Studies on the Prevention of Particle Accumulation Onto the Bogie of High-Speed Train

When high-speed train runs in the environment with a large number of airborne particles, these particles may accumulate on the bogie of the train, which will further challenge the normal operation of the bogie and reduce the riding comfort and train safety. In order to prevent particles entering into the bogie area, different protective devices around the bogie are used. However, up to present, the systematical analysis on the protective effects of diverse protective measures against different types of particles are still very limited. In this study, with the widely-used shirt boards and spoilers as protective devices, the airborne particle transport processes around the bogie were simulated in the wind tunnel Lab. Three kinds of typical particles, including artificial snow particle, wheat bran (substitute of snowflake) and sieved soil, were chosen to represent different airborne particles under real conditions. Three evolution indexes, including the relative reduction ratio of artificial snow particles, the relative particle flux reduction ratio of fine wheat bran, and the relative concentration reduction ratio of fine sieve soil particles, were used to assess their protective effects. Results showed that the combination of short-skirt board and straight triangular spoiler (i.e., in A5 case, the straight triangle spoilers installed at the front and rear ends of the train bogie, and the short-skirt boards installed on both sides of the train bogie) was the best protection with the studied three particles. The relative reduction ratio of the average snow mass in this case was 75.59%, the relative reduction ratio of the flux in the level of fine wheat bran exceeded 78%, and the relative reduction ratio of the fine soil particle concentration was more than 96%.