In highway construction across the southeastern coastal regions of China, granite residual soil is widely used as subgrade fill material in pavement engineering. Its mechanical behaviour under dynamic loads warrants in-depth investigation. Dynamic events such as vehicular traffic and earthquakes are complex, involving multidirectional loads. The dynamic behaviour of soil under bidirectional cyclic loading differs significantly from that under cyclic loading in one direction. A large-scale bidirectional cyclic direct shear apparatus was utilised to carry on a series of horizontal cyclic direct shear tests on granite residual soil with water contents of 14% and 24% at different normal stress amplitudes (sigma a) (0, 100, 200 kPa). Based on these tests, discrete element method (DEM) models were developed to simulate the laboratory tests. The test results revealed that cyclic normal stress increases dynamic shear strength during forward shear but reduces it during reverse shear. The energy dissipation capacity increases with rising sigma a. The dynamic behaviour of granite residual soil is more significantly affected by cyclic normal stress when the water content is higher. The DEM simulation results indicated that as cyclic shearing progresses, the location of the maximum principal stress (sigma 1) shifts from the top of the specimen toward the shear interface. The distribution of the angle between sigma 1 and the x-axis, as well as sigma 1 and the z-axis, transitions from 'M' distribution to 'Arch' distribution. With increasing sigma a, during forward shear, the magnitude of the maximum principal stress increases, and the orientation of sigma 1 rotates toward the normal direction. Conversely, during reverse shear, the magnitude of the maximum principal stress decreases, and its orientation shifts toward the horizontal shear direction. The material fabric anisotropy coefficient decreases with increasing sigma a, while the anisotropy orientation increases with increasing normal stress.
The study of the damage effects resulting from the explosions of cylindrical charges holds significant importance in both military and civilian fields. In contrast to spherical charges, the explosive characteristics of the cylindrical charge exhibited spatial irregularities. To comprehensively quantify the influences of borehole diameter and buried depth on the damage effects, including the crater size and stress wave, experimental and numerical investigations on explosions induced by cylindrical charge are carried out in this paper. Firstly, a set of tests is conducted to provide fundamental data. Then, based on the meshfree method of Smoothed Particle Galerkin (SPG) and the K&C model, the variations in crater dimensions and the peak stress are fully simulated with a range of borehole diameters and buried depths. Finally, the influence of borehole and buried depth on the coupling factor is discussed. Both the buried depth and the borehole diameter impact the utilization of blast energy enormously. Furthermore, materials with distinct impedance values exert an influence on the distribution of the stress wave. Following the dimensional analysis, several empirical formulae expressing the crater size and peak stress are established, all of which can predict explosion damage rapidly and accurately.
Due to the serious environmental pollution generated by plastic packaging, chitosan (CS)-based biodegradable films are gradually gaining popularity. However, the limited antioxidant and bacteriostatic capabilities of CS, the poor mechanical properties and water resistance of pure CS films limit their widespread adoption in food packaging. In this study, new multifunctional bioactive packaging films containing monosaccharide-modified CS and polyvinyl alcohol (PVA) were prepared to address the shortcomings of pure CS films. Initially, Maillard reaction (MR) products were prepared by conjugating chitosan with galactose/mannose (CG/CM). The successful preparation of CG/CM was confirmed using UV spectroscopy, fluorescence spectroscopy, fourier transform infrared spectroscopy (FTIR) and high-performance gel permeation chromatography (HPGPC). At an 8 mg/mL concentration, the DPPH radical scavenging activities of CM and CG were 5 and 15 times higher than that of CS, respectively. At the maximum concentration of 200 mu g/mL, both CM and CG exhibited greater inhibitory effects on the growth of Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli, compared to CS. Additionally, CM and CG demonstrated significantly stronger protection against oxidative damage in Vero cells than CS. These results indicate that CG and CM possess superior antioxidant and antibacterial capabilities in comparison to CS. Then, the effects of the MR on the structures and functional properties of chitosan-based films were extensively examined. Compared with pure CS films, the MR in the CG/CM films significantly changed the film microstructure, enhanced the UV-barrier property and water resistance, and only slightly reduced thermal stability. The MR reduced the tensile strength but increased the elongation at break. Meanwhile, the composite films hold good soil degradation ability. Moreover, the CG/CM films possessed excellent antioxidant and antibacterial properties and demonstrated superior fresh-keeping capacity in the preservation of strawberries and cherry tomatoes (effectively prolonged for at least 2 days or 3-6 days). Our study indicates that CG/CM films can be used as a promising biodegradable antioxidant and antibacterial biomaterial for food packaging.
In order to investigate the frost-heaving characteristics of wintering foundation pits in the seasonal frozen ground area, an outdoor in-situ test of wintering foundation pits was carried out to study the changing rules of horizontal frost heave forces, vertical frost heave forces, vertical displacement, and horizontal displacement of the tops of the supporting piles under the effect of groundwater and natural winterization. Based on the monitoring condition data of the in-situ test and the data, a coupled numerical model integrating hydrothermal and mechanical interactions of the foundation pit, considering the groundwater level and phase change, was established and verified by numerical simulation. The research results show that in the silty clay-sandy soil strata with water replenishment conditions and the all-silty clay strata without water replenishment conditions, the horizontal frost heave force presents a distribution feature of being larger in the middle and smaller on both sides in the early stage of overwintering. With the extension of freezing time, the horizontal frost heave force distribution of silty clay-sand strata gradually changes from the initial form to the Z shape, while the all-silty clay strata maintain the original distribution characteristics unchanged. Meanwhile, the peak point of the horizontal frost heave force in the all-silty clay stratum will gradually shift downward during the overwintering process. This phenomenon corresponds to the stage when the horizontal displacement of the pile top enters a stable and fluctuating phase. Based on the monitoring conditions of the in-situ test, a numerical model of the hydro-thermo-mechanical coupling in the overwintering foundation pit was established, considering the effects of the groundwater level and ice-water phase change. The accuracy and reliability of the model were verified by comparison with the monitoring data of the in-situ test using FLAC3D finite element analysis software. The evolution of the horizontal frost heaving force of the overwintering foundation pit and the change rule of its distribution pattern under different groundwater level conditions are revealed. This research can provide a reference for the prevention of frost heave damage and safety design of foundation pit engineering in seasonal frozen soil areas.
Freeze-thaw cycles (FTC) influence soil erodibility (K-r) by altering soil properties. In seasonally frozen regions, the coupling mechanisms between FTC and water erosion obscure the roles of FTC in determining soil erosion resistance. This study combined FTC simulation with water erosion tests to investigate the erosion response mechanisms and key drivers for loess with varying textures. The FTC significantly changed the mechanical and physicochemical characteristics of five loess types (P < 0.05), especially reducing shear strength, cohesion, and internal friction angle, with sandy loam exhibiting more severe deterioration than silt loam. Physicochemical indices showed weaker sensitivity to FTC versus mechanical properties, with coefficients of variation below 5 %. Wuzhong sandy loess retained the highest K-r post-FTC, exceeding that of the others by 1.04 similar to 2.25 times, highlighting the dominant role of texture (21.37 % contribution). Under different initial soil moisture contents (SMC), K-r increased initially and then stabilized with successive FTC, with a threshold effect of FTC on K-r at approximately 10 FTC. Under FTC, the K-r variation rate showed a concave trend with SMC, turning point at 12 % SMC, indicating that SMC regulates freeze-thaw damage. Critical shear stress exhibited an inverse response to FTC compared to K-r, displaying lower sensitivity. The established K-r prediction model achieved high accuracy (R-2 = 0.87, NSE = 0.86), though further validation is required beyond the design conditions. Future research should integrate laboratory and field experiments to expand model applicability. This study lays a theoretical foundation for research on soil erosion dynamics in freeze-thaw-affected areas.
Friction characteristics are critical mechanical properties of clay, playing a pivotal role in the structural stability of cohesive soils. In this study, molecular dynamics simulations were employed to investigate the shear behavior of undrained montmorillonite (MMT) nanopores with varying surface charges and interlayer cations (Na+, K+, Ca2+), subjected to different normal loads and sliding velocities. Consistent with previous findings, our results confirm that shear stress increases with normal load. However, the normal load-shear stress curves reveal two distinct linear regions, indicating segmented friction behavior. Remarkably, the friction coefficient declines sharply beyond a critical pressure point, ranging from 5 to 7.5 GPa, while cohesion follows an inverse trend. The elevated friction coefficient at lower pressures is attributed to the enhanced formation of hydrogen bonds and concomitant changes in density distribution. Furthermore, shear strength was observed to increase with sliding velocities, normal loads, and surface charges, with Na-MMT exhibiting superior shear strength compared to KMMT and Ca-MMT. Interestingly, the friction coefficient shows a slight decrease with increasing surface charge, while ion type exerts a minimal effect. In contrast, cohesion is predominantly influenced by surface charge and remains largely unaffected by ion type, except under extreme pressures and velocities.
Tree destruction induced by heavy rainfall, an overlooked type of forest degradation, has been exacerbated along with global climate change. On the Chinese Loess Plateau, especially in afforested gully catchments dominated by Robinia pseudoacacia, destructive rainfall events have increasingly led to widespread forest damage. Previous study has manifested the severity of heavy rainfall-induced tree destruction and its association with topographic change, yet the contributions of tree structure and forest structure remain poorly understood. In this study, we quantified the destroyed trees induced by heavy rainfall using light detection and ranging (LiDAR) techniques. We assessed the influence of tree structure (tree height, crown diameter, and crown area), forest structure (tree density, gap fraction, leaf area index, and canopy cover), and terrain parameters (elevation, slope, and terrain relief) using machine learning models (random forest and logistic regression). Based on these, we aimed to clarify the respective and combined contributions of structural and topographic factors to rainfall-induced tree destruction. Key findings revealed that when considered in isolation, greater tree height, crown diameter, crown area, leaf area index (LAI), and canopy cover suppressed tree destruction, whereas higher gap fractions increased the probability of tree destruction. However, the synergistic increases of tree structural factors (tree height, crown diameter, and crown area) and forest structural factors (LAI and canopy cover) significantly promoted tree destruction, which can counteract the inhibitory effect of terrain on destruction. In addition, increases in tree structure or canopy density (LAI and canopy cover) also increased the probability of tree destruction at the same elevation. Our findings challenge conventional assumptions in forest management by demonstrating the interaction of tree structure and canopy density can significantly promote tree destruction during heavy rainfall. This highlights the need to avoid overly dense afforestation in vulnerable landscapes and supports more adaptive, climate-resilient restoration strategies.
Soil chemical washing has the disadvantages of long reaction time, slow reaction rate and unstable effect. Thus, there is an urgent need to find a cost-effective and widely applicable alternative power to facilitate the migration of washing solutions in the soil, so as to achieve efficient removal of heavy metals, reduce the risk of soil compaction, and mitigate the damage of soil structure. Therefore, the study used a combination of freeze-thaw cycle (FTC) and chemical washing to obtain three-dimensional images of soil pore structure using micro-X-ray microtomography, and applied image analysis techniques to study the effects of freeze-thaw washing on the characteristics of different pore structures of the soil, and then revealed the effects of pore structure on the removal of heavy metals. The results showed that the soil pore structure of the freeze-thaw washing treatment (FT) became more porous and complex, which increased the soil imaged porosity (TIP), pore number (TNP), porosity of macropores and irregular pores, permeability, and heavy metal removal rate. Macroporosity, fractal dimension, and TNP were the main factors contributing to the increase in TIP between treatments. The porous structure resulted in larger effective pore diameters, which contain a greater number of branching pathways and pore networks, allowing the chemical washing solutions to fully contact the soil, increasing the roughness of the soil particle surface, mitigating the risk of soil compaction, and decreasing the contamination of heavy metals. The results of this study contribute to provide new insights into the management of heavy metal pollution in agricultural soils.
In cold regions, the strength and deformation characteristics of frozen soil change over time, displaying different mechanical properties than those of conventional soils. This often results in issues such as ground settlement and deformation. To analyze the rheological characteristics of frozen soil in cold regions, this study conducted triaxial creep tests under various creep deviatoric stresses and established a corresponding Discrete Element Method (DEM) model to examine the micromechanical properties during the creep process of frozen clay. Additionally, the Burgers creep constitutive model was used to theoretically validate the creep deformation test curves. The research findings indicated that frozen clay primarily exhibited attenuated creep behavior. Under low confining pressure and relatively high creep deviatoric stress, non-attenuated creep was more likely to occur. The theoretical model demonstrated good fitting performance, indicating that the Burgers model could effectively describe and predict the creep deformation characteristics of frozen clay. Through discrete element numerical simulations, it was observed that with the increase in axial displacement, particle displacement mainly occurs at both ends of the specimen. Additionally, with the increase in creep deviatoric stress, the specimen exhibits different deformation characteristics, transitioning from volumetric contraction to expansion. At the same time, the vertical contact force chains gradually increase, the trend of particle sliding becomes more pronounced, and internal damage in the specimen progresses from the ends toward the middle.
A significant amount of open-pit-mine broken sandstone (OMBS) is produced during open-pit mining. The mechanical strength of the loose sandstone is critical for ensuring dump slope stability and sustainable mine construction. This study investigates the modification of OMBS using artemisia sphaerocephala krasch (ASK) gum to enhance its engineering properties. Unconfined compressive strength, shear strength and permeability tests were conducted to quantitatively analyze the modification effect. And the stability was evaluated using FLAC3D simulation methods. The modification mechanism was characterized through SEM, FT-IR, XRD. The results demonstrated that the addition of 2 % ASK gum significantly improved OMBS mechanical performance and reduced permeability. Meanwhile, the failure mode of OMBS changed with the ASK gum content increasing. The simulation result indicated the stability of modified dump slope was better under the drying-wetting cycle. From the perspective of microstructure and chemical characteristics, the addition of ASK gum created new hydrogen bonds through intermolecular interactions with the hydrophilic groups between OMBS particles and formed a dense and stable structure through three reinforcement modes: surface encapsulation, pore filling, and bonding connection. This study provides a new idea for resource saving and environmentally friendly mining area development.