Fine Soil Research Articles

Study Some Physical Properties For Soil In Tuz khormatu North Of Iraq

In this research, a study of some physical properties for the soil of tuz khormatu have been achieved of evaluating these properties represented by physical properties for five locations with different depths. The results of Particle size analysis have showed that the soil of study area is not homogeneous and it contains a wide range of particle sizes and difference in particle sizes ratio that form the soil. The coarse soil is dominating in the study area with varying ratios with less ratios of fine soils. The coarse and fine sedimentations comes successively because of the successive flood waves. whereas most results of Atterburg limits showed that the fine soil has moderately plastic. and The specific gravity values for fine soil has ranged between (2.59-2.88) whereas The specific gravity for coarse soil (2.64-2.66).and the compaction results have showed that the maximum dry density for fine soil has ranged (1.845-2.006)g/cm3 and the optimum moisture content (10.33-12.3)% while the maximum dry density of coarse soil is (2.285-2.306) g/cm3 and the optimum moisture content (4.725-5.275)%. And the results of (C.B.R) for two samples of coarse soil (73-120)% at (95%)of compaction

Desiccation cracks prediction using a 3D finite elements model

ABSTRACT This paper focuses on the cracking of fine soil grains by desiccation using a 3D hydro-mechanical model. It further seeks to study the cracks growth across the depth during the desiccation time. Numerical results provide data for assessing the depth propagation of the cracks, field suction in 3D, the tensile stresses caused by the cracks. Cross sections have been considered to determine the cracks’ depth. Furthermore, water content and suction versus time have been obtained. It is still challenging to experimentally obtain a sample’s suction, water content, and distribution of stresses. Although there is a gap between numerical and experimental results concerning the appearance time of the first crack, the interpretation given in the text demonstrates that it is a wrong gap. Consequently, it can be stated that the numerical results agree with the experimental results, in terms of cracks intensity factor (CIF) and the evaporation rate as functions of desiccation time.

A framework for estimating all-weather fine resolution soil moisture from the integration of physics-based and machine learning-based algorithms

Due to the effects of radio frequency interference and the limitations of algorithms under specific conditions, most of the currently available microwave-based soil moisture (SM) products are spatially discontinuous and have coarse spatial resolution, whereas optical observations also reveal various data gaps due to cloud contamination. Hence, the prediction of SM over invalid pixels and disaggregation from coarse to high scales are two main processes for obtaining SM at fine spatiotemporal resolution (e.g., daily/1-km). In the present study, two methods with respect to disaggregation-first or prediction-first were investigated from the synergetic use of the widely recognized European Space Agency-Climate Change Initiative (ESA-CCI) SM product and Moderate Resolution Imaging Spectroradiometer (MODIS) images over the Tibetan Plateau (TP) region. Specifically, the Disaggregation based on Physical And Theoretical scale Change (DisPATCh) algorithm and the generalized regression neural network (GRNN) were implemented in the disaggregation and prediction, respectively. In DisPATCh, spatially complete land surface temperature (LST), normalized difference vegetation index (NDVI) and digital elevation model (DEM) were provided as essential inputs to downscale the microwave-based ESA-CCI to a spatial resolution of 1 km, whereas MODIS-derived LST, NDVI, land surface albedo and DEM were considered in the GRNN prediction. Following the two methods, the daily/1-km SM dataset over a period of three years was finally estimated. Assessments with ground in-situ SM measurements over the TP region reveal an acceptable accuracy with unbiased root mean square errors of ∼ 0.06 m3/m3, indicating the potential to obtain operational daily/1-km spatially continuous SM products in future developments.

Laboratory Assessment for Filling Materials Used for Construction Kasha Chai Embankment /Kirkuk /Iraq

Laboratory evaluation has been done , for raw data results of test and analysis for fine soil( filling materials) which it using in core construction dam, also to coarse soil (cover soil) for the same dam , according to International (American, British) & Iraqi standers.
 The treatment for fail raw data results are done, with blending many times river sand washing &cleaning, passing sieve (2) mm by using fineness equations (1,2) as, (25%) sand and (75%) fine soil, which it be concerned with American standard (fig. A, for filling materials), also blending many times river sand (15%) with (85%) coarse soil, it become concerned with American standard (Fig. B, for coarse soil) , anthers properties , concerned with world standards.

Simulation of debris flow-barrier interaction using the smoothed particle hydrodynamics and coupled Eulerian Lagrangian methods

Debris flow events occur when fine soils and sediments are mixed with water, transporting coarse objects such as boulders and woody vegetation (debris) in a fast-moving down-slope flow. As such, debris flow can have catastrophic consequences for the environment, surrounding infrastructure and human life. The mitigation of damage caused by debris flow events is often addressed by rigid and flexible barriers placed in key locations to impede flow. The numerical simulation of interactions between large debris flow events and protective structures necessitates computational methods that model large deformation and flow behaviour as well as barrier performance. Although various numerical methods exist for debris flow modelling, the benefits of each method remain unclear when coupled with the analysis of protective structures. This research investigates debris flow-barrier interaction using two distinct numerical methods – the Coupled Eulerian-Lagrangian Method (CEL) and Smoothed Particle Hydrodynamics (SPH). The capabilities and limitations of each method are presented, highlighting the differences in computational cost. The results of simulations indicate preferable methods for modelling fluid-structure interaction for assessing the performance of debris flow-protective barrier structures. • The application of CEL and SPH methods in modelling of debris is investigated. • The capabilities and limitations of each method are studied. • Simulation of debris flow-boulders-barrier interactions is presented. • The effect of mesh and particle density is explained.

Responses of Fine Root Traits and Soil Nitrogen to Fertilization Methods and Nitrogen Application Amounts in a Poplar Plantation

Inappropriate fertilization management practices have led to low timber production in intensive plantation systems in China. Thus, optimized conventional or advanced fertilization management practices are needed. We aimed to quantify whether optimized furrow fertilization (FF) is comparable to advanced drip fertigation (DF) and to make recommendations regarding fertilization management strategies for poplar plantations. A completely randomized block design experiment with two fertilization methods (DF and FF) and four N application amounts (F0: 0, F1: 68, F2: 113, and F3: 158 kg N·ha−1·yr−1) was carried out on a Populus × euramericana cv. ‘Guariento’ plantation. Fine root biomass density (FRBD), fine root length density (FRLD), specific root length (SRL), soil total nitrogen (STN), soil inorganic nitrogen (SIN), soil ammonium (NH4+-N) and nitrate nitrogen (NO3−-N) were measured. The productivity increment was calculated based on tree surveys. The results showed that FRBD and FRLD decreased with the soil depth, and more than 86% was distributed within the 40 cm soil depth. FRBD, FRLD, productivity increment and soil N increased with an increasing amount of N application. DF treatments achieved 117%, 94% and 10% higher FRBD, FRLD and productivity increments, respectively, than did FF treatments. The averages of STN, SIN, NH4+-N and NO3−-N under FF were higher than those under DF, leading to higher concentrations of residual NO3−-N in deep soil. Beneficial management practices for fine root growth were evaluated in the following order: water coupled with N > only N ≥ only water > control. FRBD was positively correlated with the productivity increment. Therefore, fine root extension to increase soil resource absorption yields greater productivity under DF treatments. Drip fertilization is recommended as a better fertilization method to greatly promote the growth of fine roots, as well as productivity and residual lower soil N for poplar plantations.

Spatial variations and the key driving factors of soil losses on dolomite slopes

We selected a typical dolomite slope and set up three micro-plots (projection length was 2 m, width was 1.2 m) on the upper, middle, and lower slopes to analyze the variations of soil losses and the key influencing factors during two hydrological years (2020-2021). The results showed that soil losses at different slope positions on dolomite slopes followed an order of semi-alfisol in lower slopes (386 g·m-2·a-1) > inceptisol in middle slopes (77 g·m-2·a-1) > entisol in upper slopes (48 g·m-2·a-1). Downward along the slope, the positive correlation gradually increased between soil losses and surface soil water content, as well as rainfall, while it gradually decreased with the maximum 30 min rainfall intensity. The meteorological factors affecting soil erosion on the upper, middle and lower slopes were the maximum 30 min rainfall intensity, precipitation, average rainfall intensity and surface soil water content, respectively. Soil erosion processes on upper slopes were mainly driven by raindrop splash erosion and infiltration-excess runoff, while that on lower slopes were mainly driven by saturation-excess runoff. The volume ratio of fine soil in the soil profile was the key factor of soil losses on dolomite slopes, with an explanation rate of 93.7%. The lower slope was the key site of soil erosion in the dolomite slopes. Subsequent rock desertification management should be based on the erosion mechanism of different slope positions, while control measures should be arranged according to local conditions.

Legacy earthen berms influence vegetation and hydrologic complexity in the Altar Valley, Arizona

Across the American Southwest water development has played a critical role in managing rangelands. Earthen berms have been constructed throughout US rangelands to manage runoff and reduce erosion. The berms altered runoff patterns to increase soil moisture with positive local vegetative response. However, altered runoff patterns can be considered a disturbance that affects broader scale vegetation patterns. We hypothesized that the hydrologic impacts of earthen berms in semiarid rangelands will be reflected in contrasting upslope and downslope vegetation patterns. A supervised classification of grass, shrubs, and bare soil was performed using orthographic imagery taken in June 2016 to quantify the effects of 181 earthen berms in the uplands and floodplain of the Altar Valley in Southern Arizona, US. Intact berms blocked runoff, creating downslope runoff “shadows” within which the precipitation is the dominant water input. We documented more bare soil downslope of intact berms in comparison with upslope. Grass and shrub cover affected by berms were related to soil texture. Grass and shrub cover were not different above and below intact berms on fine textured soils, but on sites with coarser textured soil, grass cover was lower downslope of berms. Where breaches occurred on coarser textured soils, the up and downslope differences in grass cover diminished. This study points to the role of conservation structures in adding additional complexity to already heterogeneous landscapes by creating patchwork assemblages of vegetation and bare soil proximal to earthen runoff and erosion control berms.

Influence of Induced Variability of Unsaturated Soil Parameters on Seepage Stability of Ancient Riverbank

In the restoration of ancient water engineering, the loss of fine soil particles from the ancient riverbank can easily cause seepage instability problems such as piping during the flood transient process. This paper explores the influence mechanism of flood fluctuation on soil seepage stability based on indoor experiments, field monitoring and saturated-unsaturated soil seepage theory. The paper obtains the soil-water characteristic curve of unsaturated soil using laboratory tests, builds the transient seepage finite element model of porous media and modifies parameters monitoring data to verify the numerical analysis results. The results showed that the groundwater level, pore water pressure and seepage hydraulic gradient had changed. The maximum pore water pressure between the ancient riverbank and antiseepage structure increased by 13.4%, the maximum hydraulic gradient at the toe of the riverbank increased by 49.3% and the instability of seepage significantly increased. Through the modified lime grouting between the ancient riverbank and the antiseepage structure, the structure of the soil mass was changed, and the maximum hydraulic gradient was reduced by 55.6%, which restrains piping damage. This study can be used in the restoration of ancient riverbanks to solve piping problems.

An experimental study on influence of grain-size composition on collapsing erosion of granite residual soil

Severe collapsing erosion frequently occurs in South China, where granite residual soil is widely distributed and causes a serious loss of water and soil. The grain-size composition of the granite residual soil varied significantly, resulting in a remarkable variation in the collapsing erosion. The effect of grain-size composition on the morphological characteristics of collapsing erosion is rarely studied. Therefore, in this study, laboratory-scale experiments were conducted on the slopes of granite residual soil with three different grain-size compositions using self-designed rainfall simulation equipment to investigate the influence of the grain-size composition on the evolution of collapsing erosion. The erosion process, morphological characteristics, moisture content, and soil temperature of the collapsing erosion were simultaneously monitored during the experiments. The results show that the main erosion factors and their effects vary significantly for slopes with different grain-size compositions. The damage induced by ephemeral gully erosion and gully erosion is slighter on slopes with more gravel because the gravel can effectively resist the shear stress of runoff. However, on a slope with fine soil, the depth of gullies increases rapidly, causing significant gully erosion and serious soil collapse. Moreover, both the average width and width-to-depth ratio of the rills or gullies increased with gravel content. The infiltration rate is lower and the moisture content increases slower for slopes with higher gravel content, because the existence of gravel prolongs the infiltration path of rainfall and results in earlier runoff and a higher runoff rate. However, in a slope with fine soil, a high infiltration rate induces a sharp increase in the moisture content, accompanied by severe collapsing erosion. A deeper temperature diffusion range of the slope with more gravel was observed because the preferential flow through larger pores in the soil with higher gravel content induces a deeper wetting front.

Soil organic carbon accumulation along a chronosequence of vegetation colonization on debris flow fans in Southwest China

Soil is one of the largest terrestrial carbon (C) storages, which offers great potential to mitigate climate change through C sequestration. In this study, we focused on soil organic carbon (SOC) accumulation along a chronosequence of vegetation colonization on inactive debris flow fans by investigating the temporal variation of SOC concentrations and properties such as C:N ratios, δ13C values and chemical compositions of soil fractions in both topsoils (0–10 cm) and subsoils (40–50 cm) with vegetation colonization. We found that SOC concentration increased with soil property improvement (such as increase of soil aggregation and cation exchange capacity). Petrogenic OC from parent materials and biospheric OC from vegetation are the two main sources of SOC, and vegetation colonization increased the fraction of biospheric OC in bulk SOC. Fine soil fractions were found to have higher C concentrations, i.e. higher C adsorption efficiency per unit soil mass. As a result, fine soil particles were more enriched in alkyl and O-alkyl C that are the main composition of biospheric OC added to soils after vegetation colonization. Our results show that vegetation colonization on debris flow fans not only increases SOC concentrations, but also makes the bulk SOC become more labile.

Investigation of Water and Soil Migration and Mud Pumping of Subgrades under Traffic Load

Atmospheric precipitation leads to the increase of moisture in the subgrade. The moisture and soil migration in subgrade is a key scientific problem in evaluating the service performance of the subgrade and resolving or preventing mud pumping. Using a self-developed testing system as well as a numerical simulation model, a detailed study of the dynamic hydraulic characteristics, water migration mechanism, fine soil migration mechanism, and mud pumping properties of the subgrade was conducted. The results showed that water migrated into the upper layer of the subgrade under traffic load. Meanwhile, a pressure gradient for the pore water was generated in the subgrade. This kind of pressure gradient is beneficial for the moisture and fine soil migration. With rising groundwater level and increasing traffic load, the porosity of the subgrade soil differs at different depths. The fine soil migration is caused by water migration, which causes new migration channel for water in the subgrade. Then, a circulating system of moisture and fine soil is formed in the subgrade under a traffic load. After that, the upper layer subgrade soil is nearly saturated under the action of traffic load. Then, the nearly saturated soil liquefies instantaneously, becoming mud, under the action of traffic load. However, as the loading time progresses, the moisture and fine soil in the subgrade continue to migrate upward, resulting in the mud being pumped into the ballast and the gradual disappearance of liquefied soils at different depths.

Trace metal fate in soil after application of digestate originating from the anaerobic digestion of non-source-separated organic fraction of municipal solid waste

Introduction: Digestate originating from anaerobic digestion of non-source-separated organic fraction of municipal solid waste (OFMSW) is produced abundantly worldwide and generally discarded in landfills. However, it can be a valuable resource for many bioeconomy strategies as land restoration, only if a consolidated understanding of the contaminants’ presence and behaviour in digestate-amended soil is achieved. This study aimed to investigate the fate of trace metals, namely Zn, Cu, Pb, and Cr found in the digestate, along the soil profile after digestate application on soil, and the influence that other contaminants as pharmaceutical compounds can have on their behaviour in the soil system.Methods: For that, a 90-day soil column experiment was conducted using a fine loamy sand soil topped with a layer of digestate-amended soil. Digestate-amended soil had a soil to digestate proportion of 14 to 1 (dry weight). Two experimental conditions were tested: soil amended with digestate, and soil amended with digestate spiked with the antidiabetic drug metformin. Soil samples were taken at 4 depths on days 1, 7, 21, 35 and 90, and total trace metals concentrations and fractionation were determined via atomic absorption spectroscopy.Results: Results showed that Zn, Cu, Pb ad Cr initially present in the digestate were transferred from the digestate-amended soil layer to the underlying soil layer over time, although in low amounts. Nevertheless, no transfer was detected to the deeper soil layers. Trace metals in soil were predominantly in immobile and less bioavailable forms associated with clay and silicate mineral groups, whereas in the digestate-amended soil they were in more bioavailable forms, which could be related to metals’ migration in the soil layers below. Results also show that the presence of metformin had no influence on trace metal behaviour, giving insight also on possible interactions with other potentially present contaminants as microplastics.Conclusion: The current study showed that OFMSW digestate can be a promising organic nutrient-rich matrix for land restoration even if it may contain high metals’ concentrations because low metal mobility along the soil profile can be expected.

Effect of Freeze–Thaw Cycles on Consolidation Behavior of Two Plastic Fine Soils

Effect of Freeze–Thaw Cycles on Consolidation Behavior of Two Plastic Fine Soils

Alkali Lignin-Based Hydrogel: Synthesis, Characterization, and Impact on Soil Water Retention From Near Saturation to Dryness

Highlights A lignin-based hydrogel was synthesized and shown to possess a swelling ratio of 2013%. The hydrogel contained important hydrophilic hydroxyl groups and macropores for water retention. The hydrogel improved soil water retention in silt loam soil at high matric potentials and in the dry soil range. Increasing hydrogel concentration increased water retention in a loamy fine sand soil at high and low matric potentials. Abstract. Superabsorbent polymers (hydrogels) have been proposed as soil amendments to increase the amount of plant-available water in the soil. Synthetic hydrogels have been widely investigated for use in agriculture. Due to increasing environmental concerns related to synthetic hydrogels, naturally sourced hydrogels are of interest because of their potential for increased biodegradability and biocompatibility. A lignin-based hydrogel was synthesized for this study, and its swelling properties and water absorption capacity were determined. The hydrogel was characterized using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and gas pycnometry. A hanging water column, pressure plate apparatus, and dew point potentiometer were used to measure the soil water retention curve from saturation to oven-dryness for silt loam and loamy fine sand soils after amendment with the lignin-based hydrogel. Results showed a maximum swelling ratio in deionized water of 2013% of the hydrogel’s original mass, 1092% in tap water, and 825% in a 0.9% NaCl solution. The FTIR spectra of the hydrogel showed the presence of O-H bonds from the lignin structure, which renders the hydrogel reactive to a crosslinker and forms insoluble bonds, thereby allowing the hydrogel to swell when exposed to water. SEM images of the lignin hydrogels indicate large macropores, which allowed for water absorption. Applying hydrogels significantly increased the soil's water-holding capacity at 0.3% (w/w) treatment. Hydrogel treatment significantly increased water retention at saturation or near saturation by 0.12 cm3 cm-3 and at field capacity by 0.08 cm3 cm-3 for silt loam soil at 1% (w/w) treatment compared to the control treatment with no added lignin hydrogel. Hydrogel application increased water retention over the range of the soil water retention curve from -3 to -15,000 cm for the loamy fine sand soil at 1% (w/w) treatment. However, the application of lignin-based hydrogel did not affect plant available water capacity (PAWC) in either soil tested. These results serve as preliminary evidence upon which further lignin-based hydrogel amendment studies could be built by testing higher concentrations of hydrogel in the soil. Keywords: Lignin, Soil water retention curve, Super absorbent polymers, Swelling capacity, Water retention.

Characteristics of Pile Models Injected by Low-Pressure-Injection Laboratory Setup for Chemical Improving Loose Sandy Soil

The jet grouting method for soil improvement is a novel geotechnical alternative for enhancing problematic soils where traditional foundation designs cannot provide sustainable solutions. The paper methodology was based on improving loose fine sandy soil using silica fume as a chemical additive added (with 10 percent of the cement weight) to the water and Portland cement mixes with different W/C ratios to produce pile models injected by a low-pressure injection laboratory setup that was designed and locally manufactured for this purpose. The setup design was inspired by previous research works, where its performance was validated by systematically performing unconfined compression tests (UCTs) on samples of the laboratory-injected pile models. Based on the UCTs results, high determination coefficient (R2) mathematical models were developed that related the W/C ratios of the injected mixtures to the basic parameters (cohesion, friction angle, and elasticity modulus) of the grouted pile models, validating the laboratory setup injection efficiency.

Multi-year throughfall reduction enhanced the growth and non-structural carbohydrate storage of roots at the expenses of above-ground growth in a warm-temperate natural oak forest

The more frequent occurrence and severer drought events resulting from climate change are increasingly affecting the physiological performance of trees and ecosystem carbon sequestration in many regions of the world. However, our understanding of the mechanisms underlying the responses and adaption of forest trees to prolonged and multi-year drought is still limited. To address this problem, we conducted a long-term manipulative throughfall reduction (TFR, reduction of natural throughfall by 50%–70% during growing seasons) experiment in a natural oriental white oak (Quercus aliena var. acuteserrata Maxim.) forest under warm-temperate climate. After seven years of continuous TFR treatment, the aboveground growth in Q. aliena var. acuteserrata started to decline. Compared with the control plots, trees in the TFR treatment significantly reduced growth increments of stems (−14.2%) and leaf area index (−6.8%). The rate of net photosynthesis appeared to be more susceptible to changes in soil water in trees subjected to the TFR than in the control. The TFR-treated trees allocated significantly more photosynthates to belowground, leading to enhanced growth and nonstructural carbohydrates (NSC) storage in roots. The 7-year continuous TFR treatment increased the biomass, the production and the NSC concentration in the fine roots by 53.6%, 153.6% and 9.6%, respectively. There were clear trade-offs between the aboveground growth and the fine root biomass and NSC storage in Q. aliena var. acuteserrata trees in response to the multi-year TFR treatment. A negative correlation between the fine root NSC concentration and soil water suggested a strategy of preferential C storage over growth when soil water became deficient; the stored NSC during water limitation would then help promote root growth when drought stress is released. Our findings demonstrate the warm-temperate oak forest adopted a more conservative NSC use strategy in response to long-term drought stress, with enhanced root growth and NSC storage at the expenses of above-ground growth to mitigate climate change-induced drought.

Soil texture and pH affect soil CO2 efflux in hardwood floodplain forests of the lower middle Elbe River

AbstractFloodplain ecosystems play a significant role in the global carbon (C) cycle, particularly due to their C sink potential in hardwood floodplain forests. However, in these forests, interactions between a heterogeneous micro‐relief and anthropogenic landscape changes make estimating C loss through soil CO2 efflux difficult. To determine the drivers of soil CO2 efflux, we selected six hardwood floodplain forests at the lower middle Elbe River, which were distributed among different relief positions (low‐lying or high‐elevated) in the active and former flooding zone. We measured soil CO2 effluxes over a full year using the closed‐chamber method. Based on the response of soil CO2 efflux to soil moisture and temperature, annual efflux rates were determined, which were then related to soil properties, such as pH, texture, soil organic carbon (SOC) and nitrogen (N) content. Soil CO2 efflux ranged between 1006 (±99) and 2214 (±118) gC m−2 year−1. Maximum efflux occurred in a former floodplain forest that was disconnected from Elbe River water table fluctuations. SOC‐specific soil CO2 efflux (gC gSOC−1 year−1) was smallest in low‐lying forests of the active flooding zone and reflected by the appearance of redoximorphic mottling close to the soil surface. Fine texture (<6.3 μm), SOC and N were related positively and electric conductivity, C/N and pH negatively to total soil CO2 efflux. Soil pH and fine texture were the strongest univariate predictors for total soil CO2 efflux (both R2 = 0.59). Fine texture, pH and C/N ratio explained 66% of the variance in total soil CO2 efflux according to multiple linear regression. We conclude that, in hardwood floodplain forests, soil CO2 efflux is mainly controlled by fine texture and soil pH. Fine texture can be related to soil moisture and nutrient availability and may have a positive effect on the activity of microorganisms.Highlights Soil CO2 efflux ranged between 1006 (±99) and 2214 (±118) gC m2 year−1, whereby the maximum was measured in a disconnected floodplain forest Maximum soil CO2 efflux was measured in a disconnected floodplain forest SOC‐specific soil CO2 efflux was smallest in forests where redoximorphic mottling occurred close to the surface Fine texture (<6.3 μm) and pH were the strongest predictors for annual soil CO2 efflux

Is soil an organic carbon sink or source upon erosion, transport and deposition?

AbstractSoil may be a carbon source or sink under the effect of sediment and soil organic carbon (SOC) erosion, transport and deposition. Partial SOC processes to determine whether soil subjected to water erosion is a carbon sink or source have not been clarified but are essential for increasing and predicting SOC storage. In this review, the associations between SOC mineralization, stability and stock at erosion sites, in transported sediments and at deposition sites are clarified. An overview is given for possible determination standards that define soil carbon sinks and sources. Methods for enhancing SOC sequestration and suggestions for improving SOC prediction are also presented. Particle transport is an important intermediate process that determines the material base for SOC stability and sequestration in each erosion and deposition element. When subject to water erosion, a high probability of SOC physical stabilization and a thick soil layer are essential for soil to function as a SOC sink. Sediment transport weakens SOC physical protection in eroded areas but can promote aggregation factors at deposition sites in some cases while increasing the depth of SOC in the soil. In this circumstance, a good soil environment for plant growth facilitates the occurrence of carbon sinks. A concept for critical erosion intensity is proposed to understand SOC sink determination; the concept is presented as the volume of soil erosion per square kilometre (m3 km−2) for which the maximum reduction in vegetation cover or plant biomass still permits plants to provide enough organic matter to compensate for erosion‐induced SOC loss. If erosion intensity is higher than critical erosion intensity at the erosion site, soil degradation is obvious, and soil is presented as an OC source, and vice versa. Finally, the SOC burial method for increasing the soil carbon storage amounts in regions with thick soil layers is presented to explore the SOC sequestration potential in deep soil. The factors considered for SOC prediction should vary with research scale. We hope our review will have direct implications for the modelling of SOC dynamics under water erosion on both slopes and at large scales.HighlightsChanges in soil texture and soil thickness greatly affect the amount of SOC storage at erosion and deposition sites.Selective transport of soil materials or chemical elements promotes soil aggregation.Possible standards that define soil carbon sinks and sources and suggestions for improving SOC prediction are presented.SOC burial may be a good method for increasing C storage amounts in regions with thick layers of fine soil.

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.