The aerosol size distribution, particularly the number and mass distributions, plays a crucial role in understanding changes in optical properties due to hygroscopic growth, which affects visibility and radiative forcing on a regional scale. The Indo-Gangetic Plain (IGP), including National Capital Region (NCR) of Delhi, experiences severe fog and haze with reduced visibility during the post-monsoon to winter months (October-February) every year. This study reports aerosol mass size distribution over Delhi during a winter fog campaign (December 15, 2015-February 15, 2016) using a ground-based optical particle counter. The fine and coarse mode aerosols were contributed to similar to 85% and 15% to the total aerosol mass concentration during the campaign period. The characteristic changes in aerosol size distribution, effective radius, and the influence of meteorological factors, particularly relative humidity (RH) and temperature, under three visibility conditions: Vis-1 (1200 m) were investigated. Fine-mode aerosols accounted for similar to 85 % of the total aerosol mass, with their concentration increasing by a factor of 3.7 during Vis-1 and 2.3 during Vis-2 compared to Vis-3, when the effective radius of aerosol was lowest (R-eff: 0.44 mu m). Fine particle concentrations showed a positive correlation with RH (R = 0.35) and a negative correlation with visibility (R = -0.65), suggesting that the high RH and fine-mode aerosols contribute to fog formation and reduced visibility in Delhi-NCR.

Lime stabilization is a traditional method for improving foundation soils, and it also has potential applications for embankments and earth structures. In this study, several experimental techniques, including scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR), were used to provide a clear picture of the microstructural evolution of a lime-stabilized loess (LSL) from China. SEM micrographs were used not only to qualitatively highlight the dual porosity nature of the material, but also to provide quantitative information using Image-Pro Plus (IPP) 6.0 software. As the lime content increases, the pore area ratio decreases, the shape of the macropores and mesopores flattens, and the pore angle distribution becomes more uniform. The FTIR results show that the functional group strength of the LSL samples first increases and then decreases with increase in lime content, while the pore volume continues to decrease. A non-monotonic evolution of the strength with the lime content is then expected, as also confirmed by unconfined compression tests performed at different lime contents and curing times: at low lime contents, the reduction of the pore volume and the increase in the functional group strength imply an increase in the strength; at high lime contents, the competing effects of the reduction of the pore volume and the increase in the functional group strength lead to an overall decrease in the strength with the lime content. Then, as an intermediate step toward further quantitative predictions of the hydromechanical behavior of LSL, a pore size distribution model inspired by the proposal of Della Vecchia et al. (Int J Numer Anal Meth Geomech 39:702-723, 2015) was developed and used to reproduce NMR experimental data. The pore size distribution model proved to be able to reproduce the cumulative porosity curves for the whole range of lime content and curing time studied, with only four parameters kept constant for all the simulations. The predictive capabilities of the model were also confirmed by simulating experimental data from recent literature.

Mining leads to soil degradation and land subsidence, resulting in decreased soil quality. However, there are limited studies on the detailed effects of mining activities on soil properties, particularly in western aeolian sand. This study, therefore, quantitatively assessed the aeolian sandy soil disturbance induced by mining activities in the contiguous regions of Shanxi, Shaanxi, and Inner Mongolia. The following soil physical quality indices were measured in the pre (May 2015), mid (October 2015), and postmining period (April 2016), such as the soil water content (SWC), particle size (PS), soil penetration (SP), and soil saturated hydraulic conductivity (SSHC). The results showed that mining activities brought irreversible effects on soil structures. In the pre-mining period, land subsidence broke up large soil particles, destroying soil structure, leading to decreased PS (218.33 vs. 194.36 mu m), SP (4615.56 vs. 2631.95 kPa), and subsequently decreased SSHC (1.12 vs. 0.99 cm/min). Rainfall during the midmining period exacerbated this fragmentation. Thereafter, low temperatures and humidity caused the soil to freeze, allowing the small soil particles to merge into larger ones. Meanwhile, the natural re-sedimentation, subsidence, and heavy mechanical crushing in the post-mining period increased PS and SP. The SSHC hence increased to 1.21 cm/min. Furthermore, the evaluation of soil indices from different stress zones showed that the external pulling stress zone always had a higher SSHC than the neutral zone in any mining period, possibly due to the presence of large cracks and high SWC. This study contributes to the understanding of the impact of mining activities on soil physical qualities, providing a theoretical basis and quantitative guidance for the surface damage caused by coal mining in the aeolian sandy area in Western China.

Agricultural soils are often affected by compaction due to machinery loads, which alters pore-size distribution and thus hydraulic properties. Up to date most studies on traffic and its impact on soil functions lack a detailed analysis of the effect on pore-size distribution (PSD). Our study aimed to understand how different machinery types, load levels, and moisture conditions impact the water retention curve (WRC) and PSD at various soil depths and field areas (headland or inner field). Eight field campaigns were conducted between 2016 and 2019 on a variety of sub-fields within one agricultural farm site with a clayey-silty soil. Undisturbed soil samples were collected before and after the harvest of winter wheat, silage maize, and sugar beet, and before and after digestate application. The van Genuchten model was fitted to the laboratory data, and parameters were interpreted to deduce WRC features. Additionally, the pore water pressure head at the pore-size density maximum (PSDmax) was determined and interpreted. The parameter alpha responded to all types of field traffic and decreased with increased load, indicating a shift from coarser to finer pores. The parameter n generally increased due to field traffic, suggesting a narrowed pore-size distribution. The theta s parameter, associated with porosity, decreased in all trials, with the tendency of lowest values occurring after wheeling under moist conditions. Load-induced shifts in the PSDmax towards finer pores were obvious down to 50 cm depth, even with relatively low loads. Our findings indicate that the majority of vehicles utilized in conventional agricultural operations can lead to severe soil compaction.

Forest logging activities negatively affect various soil properties. In this study, we focus on the logging effects on soil water retention and associated pore size distribution. We measured the soil-water characteristic curves (SWCCs) on 21 undisturbed samples from three research plots: a reference area, a clear-cut area and a forest track. A total of 12 SWCC points between saturation and wilting point were determined for each sample with a sand box and pressure plate apparatus. The trimodal behaviour is highlighted by the dependence between soil moisture and suction. Therefore, we proposed a revised model by combining two exponential expressions with the van Genuchten model. The exponential terms describe the influence of macro-and-structural porosities, and the latter is used to calculate textural porosity. This new model with eight independent parameters was suitable to fit trimodal SWCCs in all samples. Results revealed that logging had the most destructive effect on large pores, and the soil on the forest track was the most affected. Both soil-air and available water capacity were reduced and the permanent wilting point increased as a result of damage to the soil structure and pore system. Observed increased organic carbon content in compacted soils can be attributed to slowed decomposition due to reduced air capacity and increased waterlogging susceptibility of damaged soils.

Particle Size Distribution (PSD) exerts a substantial influence on the mechanical properties of geological materials such as rocks and soils, which can be viewed at a microscale as an assembly of discrete particles. An exploration into the effects of particle gradation on the properties of these materials provides valuable insights into their nature. In the study, the Discrete Element Method (DEM) was used to conduct numerical shear tests on eight distinct groups of slip zone soil, each characterized by a different particle gradation. The aim was to examine the meso-mechanical properties and shear evolution laws of slip zone soil numerical samples with both optimal and sub-optimal PSDs. Findings underscore the pivotal role that PSD plays in various aspects, including dilatancy, the evolution of the displacement field, the network of contact force chains, the principal stress, and the distribution of normal and tangential contact forces within the slip zone soil. It was observed that the network of contact force chains in the numerical samples with an optimal PSD was more complex than in those samples with a sub-optimal PSD. Additionally, the distribution of principal stresses before and after shear was more uniformly balanced. This particle size-based study offers significant reference value for future investigations into the impact of PSD on the macroscopic and meso-mechanical properties of slip zone soil. By augmenting this knowledge, a more comprehensive understanding of the fundamental behavior of these materials can be attained, leading to improved prediction and management of geological risks.

Gap-graded soils, extensively utilized in geotechnical and hydraulic engineering, exhibit diverse strength characteristics governed by their distinctive particle size distribution (PSD). To investigate the influence of PSD on the shear strength of gap-graded soils, this study utilizes the Discrete Element Method (DEM) to reproduce drained conventional triaxial tests of gap-graded soils across a wide range of fine particle content (FC = 1-40%) and particle size ratio (SR = 2.5-6.0). The simulation results reveal that the peak shear strength follows a characteristic unimodal curve versus FC, attaining its maximum value at about FC = 25%. SR governs peak strength through critical FC thresholds: negligible impact at FC < 10%, whereas significant enhancement occurs at FC = 25%. Micromechanical analysis reveals that branch anisotropy evolution controls strength behaviour. Shear strength inversely correlates with peak branch anisotropy as reduced branch anisotropy promotes homogenized contact force distribution. FC and SR collectively regulate macroscopic strength through coupled control of branch anisotropy evolution, where their synergistic interaction governs force chain reorganization and stress distribution homogeneity. Based on these insights, a novel predictive formula for peak strength incorporating both SR and FC were proposed, providing guidance for optimized deployment of gap-graded soils in engineering practice.

Vibroflotation has proven to be an effective method for treating loose and unevenly graded coral sand foundations formed through hydraulic filling. In this study, a series of model tests were conducted to investigate the effects of particle gradations on the response of coral sand foundation reinforced by vibroflotation. The main focus was on analyzing the changes in excess pore water pressure (EPWP) and horizontal earth pressure. Cone penetration tests (CPTs) were then used to evaluate the effectiveness of vibroflotation. The results indicate that the maximum settlement occurs after the first vibroflotation, with surface settlement significantly increasing as the distance to the vibro-point decreases. The reinforcement range expands radially, and the foundation can achieve a medium or dense state after vibroflotation. During the penetration stage, the EPWP rapidly peaks and increases with depth. Shallow foundations exhibit a higher excess pore pressure ratio compared to deep foundations. Foundations with lower coarse particle content show higher EPWPs compared to those with higher coarse particle content. Lower vibration frequency results in diminished reinforcement effects in foundations with high coarse particle content and increases the difficulty of penetration. Additionally, the residual soil pressure in foundations with high coarse particle content significantly rises after three vibroflotation reinforcements. The increase in strength after reinforcement is more pronounced because the foundation has a greater coarse particle content. The reinforcement effect diminishes with increasing distance from the vibrator.

Numerous studies have demonstrated that the strength and deformation characteristics of coarse-grained materials are significantly influenced by the initial particle size distribution (GSD). However, research on constitutive models for coarse-grained materials that consider this influence is still limited. In this study, we introduced an initial GSD index, 9, which reflects the ease of particle breakage and links the initial GSD to the ultimate GSD. We systematically investigated and elucidated the mechanism by which ,9 affects the peak shear strength (qp), peak strain (eap), and the position of the critical state line (CSL) on the e-p plane. The results regarding the effect of S on qp and eap indicate that as ,9 increases, qp decreases, whereas eap increases. Based on these findings and the hump-shaped quadratic curve model proposed by Shen Zhujiang, we established a tangent Young's modulus that considers the effects of initial GSD and confining pressure. The study on the effect of ,9 on the CSL position reveals that a decrease in S leads to a downward shift and a counterclockwise rotation of the CSL. Subsequently, within the framework of critical state soil mechanics (CSSM), we proposed a state-dependent tangent Poisson's ratio that considers the effects of initial GSD and confining pressure. For a specific type of coarse-grained material, the model only requires a set of model parameters, and the model's high accuracy is evidenced by the good agreement between the modeling results and the experimental data.

Introduction The particle size characteristics of irregular sediments in the Yangtze River Source Area (YRSA) are pivotal for understanding the mechanical properties of the sedimentary medium.Methods This study utilizes field sediment sampling, laser scanning, laboratory testing, and mathematical statistics to analyze the morphological, geometric, mineralogical, and accumulation characteristics of sediment particles in the region.Results Our findings indicate that sediments in the YRSA have angular edges and deviate from spherical shapes, exhibiting elongated and flatter three-dimensional morphologies. In the experiment, the sliding plate method was used to measure the angle of repose of the sediments, which was found to be 36.7 degrees above water and 35.9 degrees below water. Both values are higher than the typical range for non-plateau regions, indicating reduced sediment mobility. The sediments are composed of fine-grained and coarse-grained soils. The particle size distribution is primarily coarse sand (0.5-2.0 mm), fine gravel (2.0-5.0 mm), and medium gravel (5.0-20.0 mm), with a significant coarsening trend observed over the past six years. The mineral composition, dominated by quartz, feldspar, and heavy minerals, is stable, with approximately 70% of the minerals having a hardness of >= 7 on the Mohs scale. The most abundant trace elements are Ti, Mn, Ba, P, Sr, Zr, and Cl.Discussion This research reveals that the sediment characteristics in the YRSA are markedly different from those of natural sands in non-plateau regions, necessitating a reevaluation of conventional theories and engineering practices for engineering constructions in this area. The insights from this study are profound and practically relevant, illuminating the sediment transport dynamics in alpine river systems and supporting sustainable regional development.