This paper presents a comprehensive study on the evolution of the small-strain shear modulus (G) of granular materials during hydrostatic compression, conventional triaxial, reduced triaxial, and p-constant triaxial tests using 3D discrete element method. Results from the hydrostatic compression tests indicate that G can be precisely estimated using Hardin's equation and that a linear correlation exists between a stress-normalized G and a function of mechanical coordination number and void ratio. During the triaxial tests, the specimen fabric, which refers to the contact network within the particle assembly, remains almost unchanged within a threshold range of stress ratio (SR). The disparity between measured G and predicted G, as per empirical equations, is less than 10% within this range. However, once this threshold range is exceeded, G experiences a significant SR effect, primarily due to considerable adjustments in the specimen's fabric. The study concludes that fabric information becomes crucial for accurate G prediction when SR threshold is exceeded. A stiffness-stress-fabric relationship spanning a wide range of SR is put forward by incorporating the influences of redistribution of contact forces, effective connectivity of fabric, and fabric anisotropy into the empirical equation.

Gap-graded soil, characterized by the absence of certain particle sizes, is commonly used in infrastructure projects such as dams and roadbeds. A comprehensive understanding of both the macro- and micro-mechanical behaviors of discontinuously graded soils is essential for their effective use in engineering applications. In this study, drainage triaxial compression tests were conducted on four gap-graded soil samples with different fine-grain contents mainly using the DEM method, whereas the flexible boundary part was performed using the FDM-DEM method. The contacts were classified based on the magnitude of contact forces between coarse and fine particles, considering the coordination number of the particles involved and the normal angular distribution of these contacts. This classification enabled a detailed analysis of how fine particles contribute to stress transmission and structural evolution during shearing. The fabric tensor for these contact types provided further insights into the anisotropy of samples during shearing. On the microscopic scale, the evolution of contact numbers was found to closely align with the observed stress-strain behaviors. Increasing fine particle content significantly altered the role of fine particles in the stress transmission process. With low content of finer particles, initially, fine particles were situated within the voids formed by coarse particles, and the fine particles are gradually embedded into the coarse particles during the loading process. With the increase of fine particle content, fine particles constantly aggregate to block coarse particles and become the main medium of stress transmission.

Forests and grasslands often occur side by side in the landscape, forming a complex mosaic system with contrasting environmental conditions, maintained by different fire-vegetation stabilising feedbacks. Woody species that occur along this sharp gradient must adopt viable ecological strategies to deal with the contrasting environments of these ecosystems. For this, plants are challenged to efficiently coordinate the functioning of ecological strategy dimensions above- and below-ground. We tested hypotheses related to structural changes in vegetation and associated shifts in community-level trait patterns and ecological strategies during woody plant encroachment. We surveyed 60 permanent plots in forest-grassland mosaics at two different times (2012-2022) to obtain data on changes in vegetation structure, species composition, abundance and ecological strategies after 10 years without disturbance, capturing a gradient from open and woody plant-encroached grasslands to closed forests. An integrated functional approach was used to assess the different dimensions of plant trait variation, including 10 above- and below-ground traits, representing whole-plant, leaf, stem and root strategies. Woody plant encroachment led to a substantial increase in woody plant density in former grasslands, transforming their structure to resemble that of young forests. Interestingly, we found clear trade-offs between above- and below-ground traits among woody species. On the one hand, the species occurring in grassland had conservative leaves, a strategy for protection against high solar incidence, physical damage and drought, and had roots with a 'do-it-yourself' strategy, which ensures efficiency in the acquisition of nutrients and water in nutrient-limited soils, and had thick bark related to fire resistance. On the other hand, forest species were usually taller and had acquisitive leaves, indicating highly competitive ability in light-limited forests, whereas their roots had an 'outsourcing' strategy of resource uptake to mycorrhizal fungi in the nutrient-rich soils of forests. Synthesis: We advanced the current understanding of woody plant encroachment in grasslands by showing the underlying trait-based trade-offs that enable woody species to occur along the transition between forest and grassland through space and time. Importantly, we have shown how below-ground traits are important in explaining the species strategies, with a negative covariance between above- and below-ground. Our integrative trait-based approach will be helpful in better understanding and managing forest-grassland mosaics in southern Brazil and analogous patchy ecosystems around the world. Florestas e campos frequentemente ocorrem lado a lado na paisagem, formando um sistema mosaico complexo com condiçõ es ambientais contrastantes, mantido por diferentes feedbacks estabilizadores entre fogo e vegetaçã o. Espé cies lenhosas que ocorrem ao longo desse acentuado gradiente devem adotar estraté gias ecoló gicas viá veis para lidar com os ambientes contrastantes desses ecossistemas. Para isso, as plantas precisam coordenar eficientemente o seu funcionamento acima e abaixo do solo. No presente artigo nó s avaliamos mudanç as estruturais na vegetaçã o associadas com mudanç as funcionais na escala de comunidades e nas estraté gias ecoló gicas das espé cies durante o processo de adensamento de espé cies lenhosas. Para isso, realizamos a amostragem de 60 parcelas permanentes localizadas nos mosaicos campo-floresta, em dois perí odos de tempo (2012 e 2022). O objetivo foi de obter dados sobre mudanç as na estrutura da vegetaçã o, composiçã o de espé cies, abundâ ncia e estraté gias ecoló gicas apó s 10 anos sem distú rbios, capturando um gradiente que vai de campos abertos, campo adensado por plantas lenhosas até florestas fechadas. Utilizamos uma abordagem funcional integrada para aavaliar as diferentes dimensõ es funcionais das plantas, incluindo 10 atributos funcionais acima e abaixo do solo (incluindo atributos de folha, caule e raiz). O adensamento de espé cies lenhosas resultou em um aumento substancial na densidade de plantas lenhosas em á reas anteriormente ocupadas por campos, transformando sua estrutura que atualmente se assemelha à de florestas jovens. Curiosamente, identificamos claros trade-offs entre atributos funcionais acima e abaixo do solo em espé cies lenhosas. Por um lado, as espé cies ocorrendo em campos apresentaram folhas conservativas, uma estraté gia para proteçã o contra alta incidê ncia solar, danos fí sicos e seca, alé m de raí zes com uma estraté gia 'faç a você mesmo', garantindo eficiê ncia na aquisiçã o de nutrientes e á gua em solos pobres, e casca espessa relacionada à resistê ncia ao fogo. Por outro lado, espé cies de floresta foram geralmente mais altas e apresentaram folhas aquisitivas, indicando alta competitividade onde existe limitaçã o de luz, enquanto suas raí zes exibiram uma estraté gia de aquisiçã o de recursos mediada por fungos micorrí zicos, no ambiente onde os solos sã o mais ricos. Sí ntese. Avanç amos no entendimento atual sobre o adensamento de espé cies lenhosas sobre os campos ao demonstrar os trade-offs funcionais que permitem a ocorrê ncia de espé cies lenhosas ao longo da transiçã o entre floresta e campo no espaç o e no tempo. Mostramos, especialmente, como atributos funcionais abaixo do solo sã o importantes para explicar as estraté gias das espé cies, com uma covariâ ncia negativa entre atributos funcionais acima e abaixo do solo. Nossa abordagem integrativa baseada em atributos foi ú til para um melhor entendimento e manejo de mosaicos floresta-campo no sul do Brasil e em ecossistemas aná logos ao redor do mundo.

Around the world severe damages were observed due to reliquefaction during repeated earthquakes, whereas precise understanding of its mesoscopic mechanism is not much discovered. Influence of these earthquakes on reliquefaction needs to be investigated to understand its significance in contributing to inherent sand resistance. In the present study, centrifuge model experiments were performed to examine the influence of foreshocks/aftershocks and mainshock sequence on resistance to reliquefaction. Two different shaking sequences comprising six shaking events were experimented with Toyoura sand specimen with 50 % relative density. Acceleration amplitude and shaking duration of a mainshock is twice that of foreshock/aftershock. In-house developed advanced digital image processing (DIP) technology was used to estimate mesoscopic characteristics from the images captured during the experiment. The responses were recorded in the form of acceleration, excess pore pressure (EPP), subsidence, induced sand densification, cyclic stress ratio, void ratio and average coordination number. Presence of foreshocks slightly increased the resistance against EPP before it gets completely liquefied during the mainshock. Similarly, aftershocks also regained the resistance of liquefied soil due to reorientation of particles and limited generation of EPP. However, application of mainshocks triggered liquefaction and reliquefaction and thus eliminated the beneficial effects achieved from the prior foreshocks. Reliquefaction was observed to be more damaging than the first liquefaction, meanwhile the induced sand densification from repeated shakings did not contribute to increased resistance to reliquefaction. The apparent void ratio estimated from the DIP technology was in good agreement with real void ratio values. Average coordination number indicated that the sand particles moved closer to each other which resulted in increased resistance during foreshocks/aftershocks. In contrast, complete liquefaction and reliquefaction have destroyed the dense soil particle interlocking and made specimen more vulnerable to higher EPP generation. (c) 2025 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BY- NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

The development of continuously degradable and recyclable polymeric composites with superb mechanical properties, which can extend the service life of materials and reduce the environmental impact, will make a significant contribution to global sustainability. In this study, poly(vinyl alcohol) (PVA)-based composites (DPVA-Fe-TA) with degradability, recyclability and excellent mechanical properties are prepared by complexation of 3,4-dihydroxybenzaldehyde-grafted PVA (D-PVA), tannin (TA) and Fe3+ ions in dimethyl sulfoxide (DMSO), and then dialysis in deionized water and glycerol (Gly). The two-step dialysis process, playing a crucial role in reducing the free water of D-PVA-Fe-TA composites, enhances the formation of reversible of hydrogen-bonding and the reinforcement of self-assembled Fe(3+)chelation between TA and D-PVA, and facilitates the fabrication of PVA-based composites with a breaking strength of approximate to 18.7 MPa, an elongation at break of similar to 812 % and a toughness of approximate to 86.81 MJ/m(3); Meanwhile, the resulting homogeneous and dense structure of D-PVA-Fe-TA composites hinders the penetration of Gly solution, thereby enhancing the bonding strength and environmental adaptability of D-PVA-TA-Fe composites within the temperature range of-20 degrees C to 60 degrees C. Furthermore, the as- prepared D-PVA-TA-Fe composites exhibit recyclability for multiple cycles. When placed under soil culture medium, the resulting composites can be degraded without the need for manual interference. This study presents a novel strategy for the fabrication of materials possessing excellent mechanical strength, environmental adaptability, recyclability and degradation, which have great potential for taking the place of conversional composites in specific conditions.

The mechanical response of granular materials is influenced significantly by both the magnitude and strain rate. While traditionally considered rate-independent in the quasi-static regime, granular media can exhibit rate effects in certain instances. This research uses two-dimensional discrete element modelling (DEM) to investigate the rate effects in one-dimensional compression tests by comparing non-crushable with crushable granular samples. This study indicates that micromechanical properties such as particle breakage and contact force distributions are predominant factors in dictating the macroscopic responses of the material. The DEM simulations highlight differences in macroscopic changes between crushable and non-crushable samples, demonstrating a clear correlation between mechanical properties and underlying microstructural features. Notably, the distribution of contact forces varies with strain rates, influencing the degree of particle breakage and, consequently, the overall rate-dependent behaviour. Further, this study explores the impact of post-breakage contact creation and progressive force redistribution, which contributes to observable differences in macroscopic stress under varying loading rates, which is quantified using coordination number, particle velocity, and fabric tensor profiles at two loading rates.

Granular soils exhibit very complex responses when subjected to cyclic loading. Understanding the cyclic behavior of such materials is not only crucial for engineering applications but also the bottleneck of most of constitutive models. This study employs 3D Discrete Element Method (DEM) simulations to explore the accumulative plastic deformation and the internal fabric evolution within granular soils during cyclic loading. Two novel observations are identified: (1) A distinct and unique linear relationship between post-cyclic loading void ratio e and log ( p*/p 0 ) is found independent of the amplitude of cyclic load and the initial stress state prior to cyclic loading, where p* is the mean pressure incorporating cyclic loading stress and p 0 is the mean pressure prior to cyclic loading; (2) When resuming drained triaxial loadings after cyclic loadings, we observe that both microstructural and macroscopic variables converge to the same values they would have reached for pure monotonic drained triaxial loadings. This intriguing behavior underscores and extends to more general loading paths the influential and attractive power of the critical state.

This paper aims to systematically describe the mesostructural and mechanical changes in the surrounding soil of glass fiber-reinforced polymer-trapezoidal core sandwich piles (GFRP-TCSPs) under lateral loads. A lateral loading device for hydraulic gradient testing is introduced, and a corresponding numerical model is established using a continuum-discrete coupling method. The dynamic interaction between the GFRP-TCSP and the soil during incremental loading is analyzed, including the effect of the soil particle contact parameters on the pile-soil interaction (PSI), changes in the pile bending moment, and the displacement field of the surrounding soil. The development of soil force chains and changes in porosity and coordination number in different zones of the soil around the pile are investigated. The results indicate that the attraction and friction between particles are crucial for the PSI behavior of the soil. In addition, the bending moment of the pile increases with increasing lateral load but decreases when the pile inclination angle diverges significantly. Different regions of the soil around the pile exhibit different variations in average contact force, porosity, and coordination number as the GFRP-TCSP overturns. These variations provide a theoretical basis for detecting pile instability.

Particle gradation is an important feature of granular materials, which has a significant influence on the mechanical properties of soil. Several dynamic compaction (DC) tests for mono-sized dry sand samples and a well-graded dry sand sample were modeled using discrete element method. The effect of particle gradation on crater depth was analyzed as well as coordination number, porosity and contact stress from a microscopic view. It is indicated that the change rates of dynamic stress, coordination number and porosity of the well-graded sample were greater than the results from the mono-sized samples. For the mono-sized samples and the well-graded sample, the differences in dynamic contact stress, coordination number and porosity became larger as the distance of measurement point from ground surface increased. The results also demonstrate from a microscopic view that the well-graded soil and the mono-sized soil with smaller particle size were more prone to become dense under DC. This study at a grain level is helpful to understand the microscopic mechanism of DC and has a certain guiding significance to the construction of DC.

Using the coupled coordination degree model, DEA coupled coordination efficiency model, and spatial autocorrelation model, this study explored the dynamic coupled coordination relationship and spatial correlation between the ice-snow tourism network attention and tourism industry development in 31 Chinese provinces and proposed suggestions pertaining to development. Our findings showed that (1) most provinces have not yet achieved excellent coordinated development between the two systems, and the coupled coordination efficiency is low. Each province's coupled coordination degree and coordination efficiency exhibited a small increase. (2) Spatial differences in the coupled coordination level and coordination efficiency of the two systems in each province were more evident. In seven provinces, including Heilongjiang, tourism industry development demonstrated a relatively high utilization rate and enhanced ice-snow tourism network attention. (3) The rankings of the coupled coordination degree and coordination efficiency of the two systems in each province remained relatively stable at the upper and lower ends, with large changes in the central provinces. The coupled coordination efficiency of Heilongjiang, Beijing, Jilin, and Shanghai remained at the top of the list steadily, whereas Tibet, Anhui, and Qinghai stayed at the bottom. In contrast, the ranking of the coupled coordination efficiency of Inner Mongolia, Henan, and Jiangsu displayed a great change. (4) The spatial correlation analysis revealed a positive correlation that decreased annually. Some provinces exhibited characteristics of spatial aggregation, with a high-high aggregation effect in Liaoning and Jilin, a low-low aggregation effect in Gansu and Qinghai, and no spatial aggregation effect in most other provinces.