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.

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.

The mechanical properties of faecal sludge (FS) influence its moisture retention characteristics to a greater extent than other properties. A comprehensive fundamental characterisation of the mechanical properties is scarcely discussed in the literature. This research focused on bulk and true densities, porosity, particle size distribution and zeta-potential, extracellular polymeric substances, rheology and dilatancy, microstructure analysis, and compactibility in the context of using the FS as a substitute for soil in land reclamation and bioremediation processes. FSs from different on-site sanitation systems were collected from around Durban, South Africa. The porosity of the FSs varied between 42% and 63%, with the zeta-potential being negative, below 10 mV. Over 95% of the particles were <1000 m. With its presence in the inner part of the solid particles, tightly bound extra-cellular polymeric substances (TB-EPSs) influenced the stability of the sludge by tightly attaching to the cell walls, with the highest being in the septic tank with the greywater sample. More proteins than carbohydrates also confirmed characterised the anaerobic nature of the sludge. The results of the textural properties using a penetrometer showed that the initial slope of the positive part of the penetration curve was related to the stiffness of the sludge sample and similar to that of sewage sludge. The dynamic oscillatory measurements exhibited a firm gel-like behaviour with a linear viscoelastic behaviour of the sludges due to the change in EPSs because of anaerobicity. The high-TS samples exhibited the role of moisture as a lubricating agent on the motion of solid particles, leading to dilatancy with reduced moisture, where the yield stress was no longer associated with the viscous forces but with the frictional contacts of solid-solid particle interactions. The filtration-compression cell test showed good compactibility, but the presence of unbound moisture even at a high pressure of 300 kPa meant that not all unbound moisture was easily removable. The moisture retention behaviour of FS was influenced by its mechanical properties, and any interventional changes to these properties can result in the release of the bound moisture of FS.

This study investigates the influence of correlations between particle morphology and gradation on the critical shear strength of three-dimensional granular assemblies via numerical simulations. While grain shape is acknowledged to playa central role in the mechanical behavior of granular media, only a few works have explored the combined effects of grain shapes varying with grain size. Employing three-dimensional discrete- element simulations, we explore the shear behavior of samples with diverse particle size distributions, where grain shapes (ranging from spheres to very angular polyhedra) are assigned based on the relative size of each particle. Using drained triaxial shear tests, we analyze the macroscopic behavior up to large deformation levels. Micro-mechanical analyses are also conducted to understand the underlying mechanisms governing the observed macroscopic behavior, highlighting the role of grain connectivity and force transmission. Surprisingly, well graded samples composed of coarse angular grains and fine rounded ones are not capable of developing higher shear strengths than uniform samples with the same diversity on grain shapes. Conversely, samples where coarser grains are rounded and fines are angular, show constant shear strength as the particle size distribution becomes broader. These findings underscore the importance of simultaneously considering grain size and shape distributions for the assessment of realistic granular soil behavior.

This paper investigates the effects of particle morphology (PM) and particle size distribution (PSD) on the micro-macro mechanical behaviours of granular soils through a novel X-ray micro-computed tomography (mu CT)-based discrete element method (DEM) technique. This technique contains the grain-scale property extraction by the X-ray mu CT, DEM parameter calibration by the one-to-one mapping technique, and the massive derivative DEM simulations. In total, 25 DEM samples were generated with a consideration of six PSDs and four PMs. The effects of PSD and PM on the micro-macro mechanical behaviours were carefully investigated, and the coupled effects were highlighted. It is found that (a) PM plays a significant role in the micro-macro mechanical responses of granular soils under triaxial shear; (b) the PSD uniformity can enhance the particle morphology effect in dictating the peak deviatoric stress, maximum volumetric strain, contact-based coordination number, fabric evolution, and shear band formation, while showing limited influences in the maximum dilation angle and particle-based coordination number; (c) with the same PSD uniformity and PM degree, the mean particle volume shows minimal effects on the macro-micro mechanical behaviours of granular soils as well as the particle morphology effects.

Granular soil is a porous medium composed of particles with different sizes and self-similar structures, exhibiting fractal characteristics. It is well established that variations in these fractal properties, such as particle size distribution (PSD), significantly influence the mechanical behavior of the soil. In this paper, a three-dimensional (3D) Discrete Element Method (DEM) is applied to study the mechanical and critical-state behavior of the idealized granular assemblages, in which various PSD shape parameters are considered, including the coefficient of uniformity (Cu), the coefficient of curvature (Cc), and the coefficient of size span (Cs). In addition, the same PSDs but with different mean particle sizes (D50) are also employed in the numerical simulations to examine the particle size effect on the mechanical behavior of the granular media. Numerical triaxial tests are carried out by imposing axial compression under constant mean effective pressure conditions. A unique critical-state stress ratio in p '-q space is observed, indicating that the critical friction angle is independent of the shape of the PSD. However, in the e-p ' plane, the critical state line (CSL) shifts downward and rotates counterclockwise, as the grading becomes more widely distributed, i.e., the increasing coefficient of span (Cs). Additionally, a decrease in the coefficient of curvature (Cc) would also move the CSL downward but with negligible rotation. However, it is found that the variations in the mean particle size (D50) and coefficient of uniformity (Cu) do not affect the position of the CSL in the e-p ' plane. The numerical findings may shed some light on the development of constitutive models of sand that undergo variations in the grading due to crushing and erosion, and address fractal problems related to micro-mechanics in soils.