Showing papers on "Silt published in 2021"

Results of a critical state line testing round robin programme

Abstract: A critical state testing round robin programme was carried out on sandy silt gold tailings. This involved 15 laboratories around the world testing a sandy silt tailings to infer its critical state ...

Mechanical properties of calcareous silts in a hydraulic fill island-reef

Abstract: The mechanical characteristics of calcareous silt interlayers play an important role in the stability of island-reef foundations. Direct shear and consolidation tests were performed to study the re...

Machine learning applications for water-induced soil erosion modeling and mapping

Abstract: Assessment of water-induced soil erosion as a crucial part of soil conservation plans is costly and time-consuming when applied to an extensive area. In this study, we propose a methodology based on recording the annual soil erosion in a portion of the study area using erosion pins and assessing the spatial distribution of soil erosion for the entire area using machine learning techniques. First, soil erosion pins were installed, and the amount of soil loss in each pin was recorded. The controlling factors of soil erosion (percentage of vegetation canopy, curvature, slope degree, slope length, percentage of sand, percentage of silt, and percentage of clay) were determined, and the dataset was divided into training (75% of the data) and testing (25% of the data) subsets. Three machine learning algorithms, namely boosted regression trees (BRT), deep learning (DL), and multiple linear regression (MLR), were employed to identify the relationship between soil erosion and its controlling factors. Then, the methods were evaluated by comparison between the predicted and observed values on the testing subset using statistical coefficients including coefficient of determination (R-squared), normalized root mean squared error (NRMSE), and Nash-Sutcliffe efficiency (NSE). Results show that the BRT outperformed the other algorithms in the assessment of the annual soil erosion (R-squared: 0.92, NSE: 0.9, and NRMSE: 0.32). Finally, the optimal algorithm (BRT) was selected to estimate the spatial distribution of soil erosion across the entire study area, and the final erosion map was verified using additional verification pins.

Fine silt and clay content is the main factor defining maximal C and N accumulations in soils: a meta-analysis.

Abstract: When studying carbon (C) sequestration in soil, it is necessary to recognize the maximal storage potential and the main influencing factors, including the climate, land use, and soil properties. Here, we hypothesized that the silt and clay contents in soils as well as the clay mineralogy are the main factors affecting the maximal C and N storage levels of soils. This hypothesis was evaluated using a database containing the organic C contents of topsoils separated by ultrasonic dispersion to determine the particle size fractions. The slopes of the linear regressions between the C contents in silt and clay to the soil organic C (SOC) and between the N contents in silt and clay to the total N content were independent of the clay mineralogy (2:1, 1:1, calcareous soil, amorphous clays), climate type (tropical, temperate, and Mediterranean), and land use type (cropland, grassland, and forest). This clearly shows that the silt and clay content is the main factor defining an upper SOC level, which allowed us to propose a generalized linear regression (R2 > 0.95) model with a common slope, independent of the land use and climate type, to estimate the soil C sequestration potential. The implications of these findings are as follows: (1) a common slope regression was accurately calculated (0.83 ± 0.02 for C-silt + clay < 63 μm and 0.81 ± 0.02 for C-silt + clay < 20 μm) and (2) there was no asymptotic pattern found to support the existence of an SOC saturation pool.

Spatial variability of saturated hydraulic conductivity and its links with other soil properties at the regional scale.

Abstract: Saturated hydraulic conductivity (K) is a key property for evaluating soil water movement and quality. Most studies on spatial variability of K have been performed soil at a field or smaller scale. Therefore, the aim of this work was to assess (quantify) the spatial distribution of K at the larger regional scale in south-eastern Poland and its relationship with other soil properties, including intrinsic sand, silt, and clay contents, relatively stable organic carbon, cation exchange capacity (CEC) and temporally variable water content (WC), total porosity (FI), and dry bulk density (BD) in the surface layer (0-20 cm). The spatial relationships were assessed using a semivariogram and a cross-semivariogram. The studied region (140 km2) with predominantly permeable sandy soils with low fertility and productivity is located in the south-eastern part of Poland (Podlasie region). The mean sand and organic carbon contents are 74 and 0.86 and their ranges (in %) are 45-95 and 0.002-3.75, respectively. The number of individual samples varied from 216 to 228 (for K, WC, BD, FI) to 691 for the other soil properties. The best fitting models were adjusted to the empirical semivariogram (exponential) and the cross-semivariogram (exponential, Gaussian, or linear) used to draw maps with kriging. The results showed that, among the soil properties studied, K was most variable (coefficient of variation 77.3%) and significantly (p 74%) and less silty (silt content < 22%) part and, with lower K in the southern part of the study region. Generally, the spatial distribution of the K values in the study region depended on the share of individual intrinsic textural fractions. On the other hand, the ranges of the spatial relationship between K and the intrinsic and relatively stable soil properties were much larger (from ~ 15 to 81 km) than between K and the temporally variable soil properties (0.3-0.9 km). This knowledge is supportive for making decisions related to land management aimed at alteration of hydraulic conductivity to improve soil water resources and crop productivity and reduce chemical leaching.

Impact of freeze-thaw cycles on soil structure and soil hydraulic properties

Abstract: . The ploughing of soils in autumn drastically loosens the soil structure and, at the same time, reduces its stability against external stresses. A fragmentation of these artificially produced soil clods during wintertime is often observed in areas with air temperatures fluctuating around the freezing point. From the pore perspective, it is still unclear (i) under which conditions frost action has a measurable effect on soil structure, (ii) what the impact on soil hydraulic properties is, and (iii) how many freeze–thaw cycles (FTCs) are necessary to induce soil structure changes. The aim of this study was to analyse the cumulative effects of multiple FTC on soil structure and soil hydraulic properties for two different textures and two different initial structures. A silt clay with a substantial amount of swelling clay minerals and a silty loam with fewer swell/shrink dynamics were either kept intact in undisturbed soil cores taken from the topsoil from a grassland or repacked with soil clods taken from a ploughed field nearby. FTCs were simulated under controlled conditions and changes in pore structure ≥ 48 µm were regularly recorded using X-ray µCT . After 19 FTCs, the impact on hydraulic properties were measured, and the resolution of structural characteristics were enhanced towards narrow macropores with subsamples scanned at 10 µm . The impact of FTC on soil structure was dependent on the initial structure, soil texture, and the number of FTCs. Frost action induced a consolidation of repacked soil clods, resulting in a systematic reduction in pore sizes and macropore connectivity. In contrast, the macropore systems of the undisturbed soils were only slightly affected. Independent of the initial structure, a fragmentation of soil clods and macro-aggregates larger than 0.8 to 1.2 mm increased the connectivity of pores smaller than 0.5 to 0.8 mm . The fragmentation increased the unsaturated hydraulic conductivity of all treatments by a factor of 3 in by a factor of 3 in a matrix potential range of −100 to −350 hPa, while water retention was only slightly affected for the silt clay soil. Already 2 to 5 FTCs enforced a well-connected pore system of narrow macropores in all treatments, but it was steadily improved by further FTCs. The implications of fewer FTCs during milder winters caused by global warming are twofold. In ploughed soils, the beneficial seedbed consolidation will be less intense. In grassland soils, which have reached a soil structure in dynamic equilibrium that has experienced many FTCs in the making, there is still a beneficial increase in water supply through increasing unsaturated hydraulic conductivity by continued FTCs that might also be less efficient in the future.

The Impact of Soil Water Repellency and Slope upon Runoff and Erosion

Abstract: Soil water repellency (SWR) increases the amount of runoff and erosion from soils. Previous experiments on water-repellent soils had shown intricate runoff movement and high rates of water and soil losses; our aim was to observe these processes, noting their influences and quantifying impacts. The experiment used a 60 × 60 cm rainfall simulation plot setup to represent an agricultural plot with packed water repellent soil and no interference of plants. We measured inputs, and monitored surface flows and erosion on 3°, 6° and 9° slopes. A surfactant treated plot was used as a control. Eroded sediment samples were collected and measured for particle size, and together with runoff analysed for organic carbon, nitrogen and macronutrients. Runoff coefficients were high (0.53 to 0.78) for untreated soil with erosion decreasing over the course of the experiment (1.41 t ha-1 to 0.74 t ha-1 over five 2 mm rainfall events, of 2 min duration, on the 9° slope). This resulted in cumulative erosion of up to 5.35 t ha-1 after a total of 10 mm of rainfall (5 × 2 mm). Importantly, silt and clay were preferentially eroded (up to 12 × higher in eroded soil than the baseline composition) and this correlated with the loss of organic carbon, nitrogen, and macronutrients. As expected, the steepest slope (9°) caused greater runoff and erosion than the lowest (3°), however, there was no significant difference in runoff and erosion between the 6° and 9° slope. Surfactant significantly decreased runoff coefficients by two orders of magnitude compared to the untreated soil. Surface flow was initially characterised by beading and rivulet formation, minimising soil contact. Over time, however, a perched, protective water layer formed over the surface, allowing subsequent water flow with reduced soil interaction. The runoff mechanisms for these small rain events were only observed on the water-repellent soils and likely reduced the degree of erosion given the high runoff coefficients. Initial water flow also promoted armouring of the soil by the attraction of smaller particles, leading to increased loss of organic carbon and nitrogen as well as macronutrients.

The internal erosion process and effects of undisturbed loess due to water infiltration

Abstract: Internal erosion is a complex phenomenon that is one of the main risk factors to soil destruction. Its occurrence is mainly due to water infiltration and can cause slope instability. “Karst soil” is a type of loess with special soil and water sensitivity that makes it prone to landsliding. The processes of internal erosion include transport erosion and chemical dissolution, which strongly effect loess structure and strength. To reveal the internal processes and effects of the loess due to water infiltration, field investigations and indoor tests, including infiltration tests, undrained triaxial tests, particle analysis, chemical analysis, and scanning electron microscopy (SEM), were conducted. The results show that (1) the fine particles (clay and silt) and chemicals can move within the matrix of the macro-pores under seepage flow. The physical internal erosion is mainly due to fine particle migration out of the water and clay and silt particles, and the sample column settlement was 3.3 cm with a settlement ratio of 16.5%, which results in changes to the soil skeleton, increasing the porosity and infiltration rate of loess. (2) Chemical dissolution is also an important internal erosion process in loess, especially cations of Na, Mg, Ca, and K and anions of Cl, SO4, and CO3, which are mainly lost due to dissolution and flow out of with water and clay particles, resulting in altered physical characteristics of the soil. (3) Soil particles’ mitigation and chemical dissolution change the loess structure, leading to skeletal destruction and decreased peak strength and residual strength of the infiltrated sample to 7.75% and 8.13%, respectively. During internal erosion, physical fine particle migration and chemical dissolution are important for loess stability and loess slope susceptible to failure during water infiltration.

Salinity effect on the liquid limit of soils

Abstract: Previous studies stated that, with increasing salinity, the decreased liquid limit for expansive soils was attributed to the shrinkage of diffuse double layer, while the increased liquid limit for non-expansive soils was explained by the growing particle flocculation. These two mechanisms seem to be controversial and it is difficult to understand how an increasing salinity can promote soil flocculation. This study aims at clarifying the mechanism controlling liquid limit by conducting cone penetration test, sedimentation and rheological tests on MX80 Na-bentonite and silty soil. Results showed that the liquid limit and yield stress of MX80 increased then decreased with increasing salinity, while they increased slightly for the silty soil. In sedimentation test, faster settling rate and smaller sediment volume were identified for MX80 and silt suspensions in NaCl solution, evidencing the shrinkage of diffuse double layer and the formation of denser aggregated structure. This suggested that the change of liquid limit is the result of two mechanisms in competition, which depend on the compression rate of diffuse double layer: (1) the water storage in nano-fissures which correspond to the nanoscale spaces among interlayers of clay particles resulting from the slight shrinkage of diffuse double layer, and (2) the water expulsion into larger pores with significant shrinkage of diffuse double layer. For the MX80 at low salinity and for the silt soil, the first mechanism prevailed and the increasing liquid limit was attributed to the requirement of more water to fill the nano-fissures. In contrast, for MX80 at high salinity, the second mechanism prevailed—the diffuse double layer was compressed significantly, changing the double-layer water to free water and giving rise to the decrease in liquid limit.

Characterization of field-scale soil variation using a stepwise multi-sensor fusion approach and a cost-benefit analysis

Abstract: The potential of a stepwise fusion of proximally sensed portable X-ray fluorescence (pXRF) spectra and electromagnetic induction (EMI) with remote Sentinel-2 bands and a digital elevation model (DEM) was investigated for predicting soil physicochemical properties in pedons and across a heterogeneous 80-ha crop field in Wisconsin, USA We found that pXRF spectra with partial least squares regression (PLSR) models can predict sand, total nitrogen (TN), organic carbon (OC), silt contents, and clay with validation R2 of 081, 074, 073, 068, and 064 at the pedon scale but performed less well for soil pH (R2 = 051) A combination of EMI, Sentinel-2, and DEM data showed promise in mapping sand, silt contents, and TN at two depths and Ap horizon thickness and soil depth across the field A clustering analysis using combinations of mapped soil properties or proximal and remote sensing data suggested that data fusion improved the characterization of field-scale variability of soil properties The cost-benefit analysis showed that the most accurate management zones (MZs) for topsoil can be generated only using estimated soil property maps while it was the most costly as compared to other data sources For an intermediate-high (for topsoil) and high (subsoil) accuracy and a moderate economic budget, the combination of sensors (proximal + remote sensing + DEM) might be a better approach for effective MZs generation than collecting soil samples for laboratory analysis while the latter produced the most accurate maps for topsoil It can be concluded that pXRF spectra can be useful for predicting key soil properties (eg, sand, TN, OC, silt, clay) at different soil depths, and a combination of proximal and remote sensing provides an effective way to delineate soil MZs that are useful for decision-making

Characterization of Sand Production for Clayey-Silt Sediments Conditioned to Openhole Gravel-Packing: Experimental Observations

Abstract: As one of the geotechnical risks, sanding has been one of the main constraints for safely and sustainably developing marine natural gas hydrate. In this study, a cylindrical vessel that is packed with the clayey-silt sediment collected from the Shenhu area of the northern South China Sea is used to microscopically observe sand detachment, migration within matrix, invasion to gravel packing, and production for openhole gravel packing. More specifically, by injecting water from the vessel boundary, the seepage and stress-strain field for sediment near the wellbore after hydrate dissociation is simulated, and the sand failure characteristics [i.e., the produced sand volume and particle size distributions (PSDs)] are quantified. The sand failure pattern is found to largely differ from that of a sandstone reservoir, whereas fractures, wormholes, and fluidized channels are successively developed along with a large scale of sand production and inlet pressure variation. Followed is a steady flow state with a stable inlet pressure without noticeable sand failure. Correspondingly, the fracture is induced and propagated by the combinational effort of shear and tensile failure, whereas wormholes and fluidized channels are associated with the liquid dragging force. At the end of each test, foraminifera are found to accumulate near the external side of the gravel-packing region, which is beneficial to sand control. In the meantime, a compact mudcake, as an infiltration medium, is observed outside the gravel-packing layer. The 30/50 mesh gravel packing is able to control grain size up to 30.0 µm in diameter with a median of 5.0 µm, whereas the produced grains account for less than 1.0 vol% of the total sediment. By performing sensitivity analysis on sand production, depressurization shall be conducted at a small rate to not only control sand production, but also to induce flow paths at the early stage. Moreover, the sand production rate associated with fracture development is larger than those of wormholes and fluidized channels. This study focuses on the experimental observations on sand failure patterns, and the theoretical formulations and modeling will be presented and explained in a future work.3

Various textured soil as nitrous oxide emitter and consumer

Abstract: A b s t r a c t. Changes of NO3, and N2O concentrations during 34 days hypoxic incubation of eleven nitrate amended samples of the Eutric Cambisols developed from sand, silt and loam were studied. It was found that initial generation of nitrous oxide was followed, after a maximum by its subsequent absorption. The absorption rate was correlated with the efflux. Both were negatively correlated with sand content and positively with silt, clay and Corg. The percentage of nitrate reduced equals 35, 97, and 100% for Eutric Cambisols developed from sand, loam and silt, respectively. The highest N2O efflux was observed from silty soils, the lowest one from sandy soils. Total N2O consumption ranged between 3.3 and 66.5 mg N kg -1 , and consisted 32.9, 99.2, and 100% of the produced N2O for the sandy, loamy and silty soil samples, respectively. The tested soils were characterized by various ratio of the N2O emitted to the consumed. Most of sandy samples are characterized by a weak capacity to N2O production and consumption, while loamy and silty soils are characterized by a good or very good capacity to N2O production and consumption. K e y w o r d s: soil, nitrous oxide, emission, consumption, nitrate reducing

Soil detachment capacity by rill flow for five typical loess soils on the Loess Plateau of China

Abstract: The loess region of China is one of the most heavily eroded areas in the world. Soil detachment capacity by rill flow (Dc) is a key parameter for quantifying intensity of rill erosion in many process-based erosion models. However, only a limited number of studies have been devoted to soil detachment capacity for the various types of loess soil such as is found on the Loess Plateau, where there is variation from south to north and in terms of soil particle size composition. The objectives of this study were (1) to discriminate differences in soil detachment capacity by rill flow (Dc) among five loess soils, (2) to investigate the relationship between Dc and hydrodynamic parameters, and the relationship between Dc and soil properties, and (3) to establish an equation to model soil detachment capacity by rill flow for the loess region. Soil detachment capacity by rill flow for five typical loess soils found on the Loess Plateau of China was investigated through a flume experiment by varying five flow discharges and five slope gradients. The results show that Dc of SM sandy loess is the largest with a mean of 2.2145 kg m−2 s−1, followed by YL clay loess, DB sandy loess, AS loess, and CW loess. Stream power is the best hydrodynamic parameter to describe the dynamic process of soil detachment capacity by rill flow for these five loess soils. Soil detachment capacity by rill flow was negatively correlated with soil cohesion and effective silt content (P

Equations controlling the strength of sedimentary silty soil–cement blends: influence of voids/cement ratio and types of cement

Abstract: This paper presents the elaboration of equations controlling the unconfined compression strength (qu) of a silty soil treated with three types of cement. The equations were created under influence ...

Variations in soil aggregate stability due to land use changes from agricultural land on the Loess Plateau, China

Abstract: Soil aggregate stability is a feasible and effective factor to understand the complex interactions between physicochemical properties and soil structure To reveal the distributions of soil aggregate stability and its influential factors following land use change from apple orchards abandonment and development in the Nangou watershed of the Loess Plateau, China, this study selected five ages of apple orchards and their planting years were 1 year, 3 years, 6 years, 8 years and 10 years, one 15-year grassland developed from an apple orchard, one 15- year grassland developed from farmland, one natural grassland and one 15-year locust Results showed that restored vegetation had better soil aggregate stability, soil organic carbon (SOC), and nitrogen (N) than apple orchards, and the composition of soil particles with the best aggregate stability was clay 6%, silt 8%, and sand 86% At a 0–10 cm soil depth, soil aggregate stability had a significant positive correlation with SOC and soil total nitrogen (STN), and a negative correlation with NO3− and NH4+ In addition, vegetation diversity and coverage only affected the soil aggregate stability of the 0–10 cm soil depth; however, soil pH, bulk density, and soil aggregate-associated inorganic nitrogen were the main influential factors that drove the soil aggregate stability of the 0–30 cm soil depth Further research discovered that macro-aggregate associated NO3− and micro-aggregate associated NH4+ may be the key factors affecting the soil aggregate stability Therefore, it is essential to further explore the effect of soil aggregate-associated inorganic nitrogen on soil aggregate stability

Monotonic, Cyclic, and Postcyclic Responses of an Alluvial Plastic Silt Deposit

Abstract: This study presents a comprehensive investigation into the monotonic, cyclic, and postcyclic response of a medium stiff, plastic, lightly-overconsolidated, alluvial clayey silt deposit. The...