Internal erosion induces alterations in the initial microstructure of soils, simultaneously affecting physical, hydraulic, and mechanical properties. The initial soil composition plays a crucial role in governing the initiation and progression of seepage-induced suffusion. This study employs the controlled variable method to develop granular soil models with varying particle size ratios, initial fine particle contents, and coarse particle shapes. Seepage suffusion simulations coupled with microstructural analyses are conducted using the CFD-DEM approach. Results demonstrate that particle size ratio, fine particle content, and coarse particle shape exert distinct influences on cumulative erosion mass, fine particle distribution, contact fabric, and mechanical redundancy at both macroscopic and microscopic scales. This numerical investigation advances the fundamental understanding of internal erosion mechanisms and informs the development of micro-mechanical constitutive models. Furthermore, for binary granular media composed of coarse and fine particles, careful control of the particle size ratio and fine content is recommended when utilizing gap-graded soils in embankment and dam construction to improve structural resilience and resistance to internal erosion.

The accumulation of waste glass (WG) from construction and demolition waste is detrimental to the environment due to its imperishable nature; therefore, it is crucial to investigate a sustainable way to recycle and reuse the WG. To address this issue, this study examined the mechanical strength, microstructural characteristics, and environmental durability-specifically under wet- dry (WD) and freeze-thaw (FT) cycles-of WG obtained from construction and demolition waste, with a focus on its suitability as a binding material for soil improvement applications. Firstly, sand and WG were mixed, and an alkali solution was injected into the mixture, considering various parameters, including WG particle size, mixing proportions, sodium hydroxide (NaOH) concentration, and curing time. Subsequently, the effect of WG grain sizes on micro- morphology characteristics and mineralogical phases was evaluated before and after the treatment through X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and ultrasonic pulse velocity (UPV). The results revealed that reducing the WG particle size and increasing the WG/S ratio significantly improved the strength of the WG-treated samples. Additionally, decreasing the NaOH concentration and extending the curing time also positively influenced their strength. The UCS test results indicate that the particle size of WG significantly influenced the strength development of the samples, as the maximum compressive strength increased from 1.42 MPa to 7.82 MPa with the decrease in particle size. Although the maximum UCS values of the samples varied with different WG particle sizes, the values exceed the minimum criterion of 0.80 MPa required for use as a road substructure, as specified in the ASTM D4609 standard. Moreover, as WG grain size decreased, more geopolymer gels formed, continuing to fill the voids and making the overall structure denser, and the changes during geopolymerization were confirmed by XRD, SEM, FTIR, and UPV analysis. The optimum WG/S ratio was found to be 20 %, with strength increasing by approximately 3.88 times higher as the WG/S ratio shifted from 5 % to 20 %. In addition, the optimum NaOH concentration was determined to be 10 M, as higher molarities led to a decrease in strength. Moreover, UPV results indicate that WG-treated sand soils exhibited UPV values 9.4-13 times greater than untreated soils. The WD and FT test results indicate that WG-treated samples experienced more rapid disintegration in the WD cycle than in the FT cycle; however, a decrease in WG particle size resulted in reduced disintegration effects in both WD and FT conditions. In both the FT and WD cycles, the declining trend exhibited a stable tendency around the eighth cycle. Nevertheless, the WD cycling damage considerably intensified disintegration, causing a profound deterioration in the structural integrity of the samples. As a result, repeated WD cycles lead to the formation of microcracks, which progressively weaken soil aggregation and reduce the overall strength of the samples. Consequently, this green and simple soil improvement technique can provide more inspiration for reducing waste and building material costs through efficient use of construction and demolition waste.

This study aims to systematically investigate the influence mechanism of particle size and surface roughness on the shear mechanical behavior of spherical particle materials. Rough glass beads with different particle sizes (2 mm, 3 mm, 4 mm) were prepared using sandblasting technique. Together with smooth glass beads, they were used as test raw materials for indoor triaxial consolidated-drained (CD) tests. Based on the quantitative characterization of particle surface roughness, the differences in the shear mechanical properties of spherical particle materials, including stress-strain curves, strength parameters, critical state characteristics, and stick-slip behavior, etc., were discussed from the aspects of the particle size effect (R), the surface roughness index (Ra), and the normalized roughness effect (Ra/R). The main research results show that: increasing the surface roughness of particles can improve various shear mechanical parameters to a certain extent. This includes effectively increasing the peak deviatoric stress, expanding the range of the strength envelope, and raising the deviatoric stress corresponding to the specimen in the critical failure state. It can significantly increase the peak friction angle phi by approximately 10 %-40 % and the critical state line slope (CSL slope) by about 5 %-23 %. Moreover, the increase becomes more pronounced as the particle size decreases. Meanwhile, as the normalized roughness effect (Ra/R) increases, the friction coefficient becomes larger, which greatly weakens the stick-slip behavior between particles.

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.

The study area, located in Martil, northern Morocco, lies in a region with high seismic risk, near a subduction zone. As a result, loose soils, such as sands, lose their shear strength under seismic loads due to an increase in pore water pressure, leading to deformations. The objective of this study is to assess the risk of soil liquefaction at the site where the Lalla Khadija High School will be constructed. The method used to evaluate the liquefaction risk is based on in-situ test results, as proposed by Seed and Idriss (J Soil Mech Found Div 97(9):1249-1273, 1971. https://doi.org/10.1061/JSFEAQ.0000981). Specifically, the liquefaction potential is assessed using data from the cone penetration test (CPT). This methodological approach combines a qualitative evaluation of susceptibility, which identifies the presence of fill materials and Plio-Quaternary sands-potentially liquefiable materials. At this stage, a quantitative evaluation of susceptibility is performed by calculating the safety factor, defined as the ratio between the normalized cyclic resistance ratio of the soil and the normalized cyclic stress ratio induced by the earthquake. The results of the CPT indicate that the normalized penetration resistance (qc1Ncs) consistently exceeds 160, which reflects sufficient soil strength. Consequently, the analysis confirms the absence of liquefaction risk in the sandy layers between depths of 1.8 m and 14 m. Therefore, the studied site has no liquefaction potential. This study has certain limitations. It relies solely on the method of Seed and Idriss (1971) to assess liquefaction risk, thereby restricting comparisons with alternative approaches. Additionally, the analysis focuses exclusively on the Lalla Khadija High School site, preventing extrapolation to the entire Martil plain. Nevertheless, by confirming the absence of liquefaction risk at this site, the study enables optimized foundation design, ensuring the stability of the infrastructure in the event of an earthquake. This contributes to occupant safety and improved seismic risk management in the region.

Significant quantities of bark are generated during wood processing, with the majority being utilized for energy production and soil enhancement. This study investigated the influence of bark particle size and resin type (urea-formaldehyde (UF) and melamine-urea-formaldehyde (MUF)) on the properties of particleboards made from spruce and pine bark. Board samples were fabricated using different bark particle sizes (2 to 5 mm and 5 to 8 mm) and varying adhesive contents (5% and 7%) for both UF and MUF adhesives. Reference particleboards were manufactured using industrial wood particles with the same UF and MUF adhesive contents. The spruce bark consistently outperformed pine bark across most investigated properties. Board samples fabricated from spruce bark particles exhibited higher internal bond (IB) strength and modulus of rupture (MOR), as well as enhanced resistance to water absorption (WA) and thickness swelling (TS), particularly when bonded with urea-formaldehyde (UF) adhesive. Specifically, boards composed of spruce bark, using a combination of bark particle sizes, UF adhesive, and 7% adhesive content, exhibited superior performance in IB strength, water resistance, and modulus of elasticity.

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.

The direct simple shear (DSS) test serves as a vital method in geotechnics, allowing the measurement of peak and post-liquefaction shear strengths, along with the critical state friction angle of soils. Additionally, the simple shearing mode applied in a DSS test is the predominant failure mode in many geotechnical engineering problems. Although the DSS test is widely used to determine soil strength, a significant challenge with the DSS device is the non-uniformity of stress and strain distributions at the specimen boundaries. This non-uniformity depends on not only the specimen size but also the size of soil particles. The influence of specimen size on boundary effects is typically evaluated using the ratio of specimen diameter (D) to height (H). The median particle diameter (D50), as an indicator of a soil's particle size, could be another influential factor affecting the non-uniformities of stress and strain on specimen boundaries in a DSS test. Through three-dimensional discrete element method (DEM) simulations, this research explores these factors. Specimens were generated with a particle size distribution (PSD) scaled from a coarse sand sample. Laboratory monotonic DSS testing results on the coarse sand were employed to calibrate the DEM model and ascertain the modeling parameters. Boundary displacements were regulated to maintain a constant-volume condition which represents undrained shearing behavior. Various specimen diameters were simulated with identical void ratios to investigate the influence of D/H on stress path, peak and post-peak shear strengths, and critical state behavior. DEM simulations allowed the generation of several particle size distributions through different scaling factors applied to the sand gradation to determine the combined effect D50 and D/H. Limiting D/H and D50/D ratios are subsequently proposed to mitigate specimen boundary effects.

In the process of using transportation infrastructure, contact erosion between different particle sizes soil layers can easily occur under complex hydro-mechanical coupling, leading to deformation and damage of structures. To investigate indirect erosion between soil layers under cyclical load effects from a microscopic perspective, a volume of fluid-discrete element method (VOF-DEM) coupled method was adopted in this study. The influence of different water table levels and particle size ratios (PSR) was considered. The study found that: (1) The compressive effect of coarse particles during loading and the stress relaxation effect during unloading can both cause migration of fine particles within one loading-unloading cycle; (2) Immersion of the contact surface between coarse and fine particles is a key factor in inducing particle migration, with the interaction between particles being the most intense at the contact surface; (3) Fully saturated soil experiences the most severe particle erosion and macroscopic deformation; (4) Reducing PSR can effectively improve the integrity of soil structure and suppress erosion of fine particles; (5) Particle migration inevitably leads to axial deformation of the soil, resulting in reduced stiffness and increased energy dissipation during loading-unloading cycles. This study provides new insights into contact erosion under complex hydraulic coupling from a microscopic perspective.

Particle size significantly influences the macroscopic and microscopic responses of granular materials. The main purpose of previous works was to investigate the macroscopic response, but the influence of particle size on the evolution of microstructures is often ignored. The particle size effect becomes more complex under true triaxial stress conditions. Using the discrete-element method, a series of true triaxial numerical tests were carried out in this study to investigate the particle size effect. The mechanism of the particle size effect was elucidated from the perspective of similarity theory first. Then, the evolution of the stress and fabric for the whole, strong, and weak contact network was investigated. Meanwhile, the role played by strong and weak contacts in the particle size effect was discussed. The numerical results demonstrate that the peak stress ratio of the granular materials is enhanced as the particle size increases, which is caused by strong contacts. The peak stress ratio shows a linear relationship with particle size. The particle size effect on the strength is greater under the triaxial compression condition than under the triaxial extension condition. The proportion of sliding contacts within weak contacts gradually increases as the particle size increases. At nonaxisymmetric stress conditions, stress and fabric display noncoaxial behavior on the pi-plane, and an increase in particle size enhances the noncoaxiality, which mainly originates from the weak contacts.