This study presents a hierarchical multiscale approach that combines the finite-element method (FEM) and the discrete-element method (DEM) to investigate tunneling-induced ground responses in coarse-grained soils. The approach considers both particle-scale physical characteristics and engineering-scale boundary value problems (BVPs) simultaneously, accurately reproducing typical tunneling-induced mechanical responses in coarsegrained soils, including soil arching and ground movement characteristics observed in laboratory tests and engineering practice. The study also unveils particle-scale mechanisms responsible for the evolution of soil arching through the underlying DEM-based RVEs. The results show that the rearrangement of microstructures and the deflection of strong contact force chains drive the rotation of macroscopic principal stress and the formation of soil arch. The microscopic fabric anisotropy direction can serve as a quantitative indicator for characterizing soil arching zones. Moreover, the effects of particle size distributions (PSD) and soil densities on ground deformation patterns are interpreted based on the stress-strain responses and contact network characteristics of DEM RVEs. These multiscale insights enrich the knowledge of tunneling-induced ground responses and the same approach can be applied to other geotechnical engineering analyses in coarse-grained soils.

The cumulative plastic deformation and damage evolution of frozen soil-rock mixtures under cyclic loading was studied by a dynamic triaxial instrument with real-time resistivity measurement function. A series of low- temperature cyclic triaxial tests were conducted under varying confining pressures (200 kPa, 500 kPa, 800 kPa), block proportions (0, 30 %, 40 %, 50 %), and dynamic stress ratios (0.4, 0.6, 0.8). The results reveal that the cumulative plastic deformation process can be divided into three stages, such as microcrack closure as the initial stage, crack steady growth as the middle stage, and rapid crack propagation until it fails as the final stage. Under the same number of cycles, the greater the dynamic stress is, the greater the cumulative plastic deformation is. Furthermore, a strong correlation is identified between the resistivity and the cumulative plastic deformation. With the increase of the number of cycles, the cumulative plastic deformation leads to the accumulation of internal damage, and the resistivity gradually increases. Thus, a damage evolution model based on resistivity damage variables is proposed. The model demonstrated an average fitting accuracy of 97.36 % with the experimental data.

Coarse-grained soil is generally used in cold-regions infrastructure to mitigate the frost damage to engineering because of its non-frost heave susceptibility; however, in certain cases, coarse-grained fill has been observed to experience frost heave under hydraulic pressure. To reveal the mechanism of hydraulic pressure on coarsegrained soil frost heave, a model was developed to describe the frost heave in coarse-grained soil, incorporating the migration of external water to ice lenses through an unfrozen water film under hydraulic pressure, then the model was validated using published results. Subsequently, based on the validated model, the influence mechanism of hydraulic pressure and fine content on coarse-grained soil frost heave were analyzed. The calculation results demonstrate that the hydraulic pressure aggravates frost heave by increasing the pore water pressure gradient in the unfrozen water film. Additionally, frost heave rate increases with fine content because of the thickening of the film, which facilitates water flow and ice segregation. Furthermore, gray correlation analysis demonstrated that the impact of hydraulic pressure on frost heave in coarse-grained soil is more significant than that of fine content. Finally, the study discusses frost damage that occurred in high-speed railway subgrade and proposes the preventive measures.

To investigate the effects of freeze-thaw (FT) cycles on the mechanical properties of coarse-grained soil in southeastern Xizang under different moisture contents, this study focuses on coarse-grained soil from a large landslide deposit in Linzhi City, Xizang. FT cycle tests, triaxial shear tests, and numerical simulations were employed to systematically examine the comprehensive impact of varying FT cycles, moisture content, and confining pressure on the soil's mechanical characteristics. The results show that FT cycles significantly affect the stress-strain behavior of coarse-grained soil in southeastern Xizang. The degree of strain softening increased from approximately 11.6% initially to 31.2% after 15 FT cycles, with shear strength decreasing by an average of 31.8%. Specifically, cohesion decreased by 38% to 55% after 0 to 15 FT cycles, and the internal friction angle decreased by approximately 29% to 32%. Additionally, higher moisture content led to more pronounced strain softening and strength degradation, while increased confining pressure effectively mitigated these deteriorative effects. Numerical simulation results indicated that as moisture content increased from 7.6% to 11.6%, the number of FT cycles required to reach the critical instability state decreased from approximately 150 to 106, and finally to only 15, with the maximum equivalent plastic strain increasing from 0.20 to 2.47. The findings of this study provide key mechanical parameters for understanding the formation and evolution of FT landslide disasters in southeastern Xizang and lay a scientific foundation for the assessment and long-term prevention of cold-region geological hazards.

Take the reservoir landslide as an example, in addition to hydrological conditions, creep properties of soils play an important role in explaining the mechanisms behind landslide movement. Although the change of this deformation over time is small, the long-term accumulation will also bring new hidden danger to the safety control of the slope. This paper takes the shallow coarse-grained soils of Qiaotoubei landslide as the research interest, improves the test method for the deficiency of not allowing the lateral deformation of the specimen in the traditional one-dimensional compression creep test, and conducts the compression creep test of coarse-grained soils by using the modified high-pressure consolidation instrument. Based on this test data, the creep property of coarse-grained soils is analyzed and a suitable creep constitutive model is selected, that is generalized Kelvin model. Then, relevant parameters are determined and FLAC3D software is used to simulate the creep deformation of the slope deposits and the stress and deformation of the lattice beams. Finally, the coupling mechanism between coarse-grained soils creep and lattice structure was analyzed based on the comparison of the calculated results with the deformation or damage in the field. Through this study, some targeted suggestions and directions for future research are proposed for the management of reservoir deposit landslides, hoping to contribute to the operational safety of the reservoir.

Coarse-grained soils are fundamental to major infrastructures like embankments, roads, and bridges. Understanding their deformation characteristics is essential for ensuring structural stability. Traditional methods, such as triaxial compression tests and numerical simulations, face challenges like high costs, time consumption, and limited generalizability across different soils and conditions. To address these limitations, this study employs deep learning to predict the volumetric strain of coarse-grained soils as axial strain changes, aiming to obtain the axial strain (epsilon(a))-volumetric strain (epsilon(v)) curve, which helps derive key mechanical parameters like cohesion (c), and elastic modulus (E). However, the limited data from triaxial tests poses challenges for training deep learning models. We propose using a Time-series Generative Adversarial Network (TimeGAN) for data augmentation. Additionally, we apply feature importance analysis to assess the quality of the numerical augmented data, providing feedback for improving the TimeGAN model. To further enhance model performance, we introduce the pre-training strategy to reduce bias between augmented and real data. Experimental results demonstrate that our approach effectively predicts epsilon(a)-epsilon(v) curve, with the mean absolute error (MAE) of 0.2219 and the R-2 of 0.9155. The analysis aligns with established findings in soil mechanics, underscoring the potential of our method in engineering applications.

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.

The accumulation and discharge amount of coal gangue are substantial, occupying significant land resources over time. Utilizing coal gangue as subgrade filler can generate notable economic and social benefits. Coal gangue coarse-grained soil (CGSF) was used to conduct a series of large-scale vibration compaction tests and large-scale triaxial tests. The results indicate that the maximum dry density of CGSF initially increases and then decreases with the increase in fractal dimension. The stress-strain curves of the samples exhibit a distinct nonlinear growth pattern. Analysis of the compaction effect suggests that the compaction degree of CGSF should not be lower than 93%. As the confining pressure increases, the extent of failure strength improvement due to increased compaction decreases. Additionally, the failure strength of samples initially increases and then decreases with the increase in coarse particle content. A modified quadratic polynomial fractal model gradation equation was proposed to describe the gradation of samples after particle breakage. Based on this, a new quantitative index for particle breakage was established. Analysis of particle breakage in samples revealed that higher confining pressure and greater coarse particle content lead to increased particle breakage. The breakage exhibited a significant size effect, and the impact of particle gradation on sample breakage was greater than that of confining pressure. The stress-strain relationship of CGSF was analyzed by using a logarithmic constitutive model, and the correlation between model parameters and the newly derived particle breakage index was generated. A constitutive model incorporating particle breakage for CGSF was established, and its accuracy was validated.

Research on the evolutionary behavior of the particle breakage processes in coarse-grained soil under the action of train load is of practical significance for subgrade construction and maintenance. However, existing studies have not addressed the prediction of particle size distribution evolution. In this paper, the MTS loading system is used to simulate the dynamic train load effect on coarse-grained soil fillers. The study analyzes the influence of dynamic stress amplitude, loading frequency, and vibration times on both the macro-characteristics and micro-characteristics of particle breakage. The characteristics of particle fragmentation in coarse soil filler under high-speed train load are elucidated. Furthermore, a predictive model for the evolution of particle size distribution curves in relation to particle content and relative particle size is established using the ZHU continuous grading curve equation. This model captures the evolution process of particle breakage characteristics in coarse-grained soil fillers subjected to high-speed train loads. The applicability of this model has been verified. Based on the grading prediction model, an integral expression for the breakage rate index is derived, and the evolution characteristics of particle breakage in coarse-grained soil fillers under the action of train load are analyzed. The results indicate that during filling, the particle breakage mode of coarse-grained soil fillers during filling is primarily characterized by fracture and fragmentation; conversely, under dynamic cyclic loading conditions, it is predominantly characterized by fracture and grinding. The breakage rate aligns with the measured results, suggesting that the breakage rate index established in this study can effectively describe the evolution process of particle breakage in railway subgrade coarse-grained soil. After the reaching one million loading cycles, both deformation and particle breakage degree in coarse-grained soil fillers tend to stabilize. Under the action of dynamic stress amplitudes ranging from 10 to 200 kPa and loading frequencies between 2 and 12 Hz, the particle breakage index stabilizes below 1.1%. These research findings contribute to a deeper understanding of the evolutionary processes affecting engineering characteristics of railway subgrade coarse-grained soils and provide a theoretical as well as experimental foundation for railway subgrade construction and maintenance.

Purpose - This paper investigates the vibration compaction mechanism and evaluates the impact of vibration frequencies on the stability of coarse-grained soil, aiming to optimize the subgrade filling process. Design/methodology/approach - This study examines the vibratory compaction behavior of coarse-grained soils through indoor vibration tests and discrete element simulations. Focusing on angular gravel (breccias) of varying sizes, the simulations were calibrated using parameters such as Young's modulus, restitution and friction coefficients. The analysis highlights how particle shape influences compaction, revealing mesoscopic mechanisms that drive macroscopic compaction outcomes. Findings - This study investigates the influence of vibration frequency on the compaction behavior of coarse- grained soils using discrete element simulation. By analyzing particle contact and motion, the mesoscopic mechanisms driving compaction are explored. The study establishes a positive linear correlation between contact force anisotropy (Cv) and deformation, demonstrating that higher anisotropy leads to greater structural disruption. Additionally, the increase in sliding contact percentage (SCP) at higher frequencies indicates instability in the skeletal structure, driven by uneven contact force distribution. These findings reveal how frequency-induced stress concentration affects the stability and deformation of the soil skeleton. Originality/value - This research explores the effect of various vibration frequencies on the compaction behavior of coarse-grained soils, examining microscopic interactions to reveal their impact on soil stability and deformation.