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.

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 evaluation of triggering potential and induced deformations is crucial for liquefaction assessment of geosystems constructed on, or comprised of, coarse-grained soils. A series of cyclic constant volume direct simple shear (DSS) tests were simulated using the discrete element method (DEM) to investigate the influence of gradation on the pre- and post-liquefaction behavior of coarse-grained soils, including the resistance to initial liquefaction, accumulation of shear strains, and evolution of fabric. The DEM simulations were conducted on isotropically consolidated cubical specimens composed of non-spherical particles with a coefficient of uniformity (CU) C U ) range between 1.9 and 6.4. At similar relative densities, specimens with broader gradations yield lower liquefaction triggering resistance than poorly-graded specimens. However, at the same initial state parameter, the more broadly-graded specimens have higher liquefaction triggering resistance. Regardless of the parameter of state used for comparison, the specimens with broader gradation accumulate post-triggering shear strains at smaller rates than the poorly-graded specimens. The presence of coarser particles in the broadly-graded specimens promotes stable packing and enhanced interlocking by forming a substantially large number of contacts, which limits the particle movement and produces lower post-liquefaction strain accumulation. In contrast, the finer particles contribute minimally to the overall specimen stability. Additionally, wider gradations increase the anisotropy in the contact forces, with the strong forces aligning in the major principal stress direction and the weak forces providing resistance against buckling. These insights contribute to a better understanding of the pre- and post-liquefaction triggering behavior in granular soils and the implication for the design of resilient infrastructure built on, or comprised of, coarse-grained broadly-graded soils.

The paper summarises a series of research studies aimed at investigating the response of framed structures to tunnelling in coarse-grained soils. The activities were developed with a twofold objective: on the one hand, an extensive experimental campaign of centrifuge tests was designed and carried out in order to obtain a consistent set of data, although for simple geometric configurations of the structure and of the tunnel-to-structure relative position; on the other, attention was paid to the essential elements to be included in the numerical simulations, essentially in terms of tunnel excavation simulation procedures, adopted detail in the schematisation of the structural components and constitutive laws to describe the non-linear soil and structural response. Validation of numerical models, based on experimental results, allowed them to be used to extend the analysis to further configurations and to fully define the modification factors of the maximum angular distortion of the span as a function of the relative soil-structure shear stiffness. In addition to the direct comparison with the centrifuge data, the numerical strategy was also validated against in situ observations carried out over a stretch of the Milan metro line 5. This case study was also used to perform a numerical exercise, through inverse analysis and meta-modelling procedures, to optimize the position of the monitoring sensors for a possible real-time calibration of the soil constitutive and TBM-EPB machine parameters used in the numerical modelling.