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.

Soil-steel composite bridges (SSCBs) are commonly utilized as overpasses. In the majority of existing studies, the transverse structural performance of SSCBs is primarily focused on, while neglecting their longitudinal structural performance. The aims of this paper are to clarify the longitudinal properties and compensate for the paucity of research on the longitudinal structural performance of SSCBs. In current study, field tests were conducted on a SSCB case bridge in a mining area, both in the construction stage and post-construction stage. Subsequently, longitudinal differences in the structural settlements, deformations, and hoop strains were analyzed. Additionally, a refined three-dimensional finite element model was developed and verified to analyze the transfer behavior of soil pressure above the structure along the longitudinal direction. The results indicate that in the construction stage, the difference in the soil-covered height primarily account for the differences in structural performances along the longitudinal direction. At the end of backfilling, the settlements, deformations, and hoop strains in the middle are all greater than those in the end sections. In the post-construction stage, further developments of longitudinal structural characteristics occur due to creep deformation of the foundation soil and disturbances from mining trucks. One year after construction, the structural characteristics have stabilized. The maximum settlement reaches -1.014 m and the maximum settlement difference reaches 0.365 m. The differential settlement ratio, at 0.62 %, remains within the 1 % limit specified in the CHBDC code. Due to longitudinal settlement differences, the soil pressure in the higher settlement zone is transferred to the lower settlement zone by the longitudinal soil arching effect, which benefits the load-bearing capacity of SSCBs.

Stress release of the surrounding soil is the fundamental reason for many accidents in tunnel engineering. There have been a great number of numerical simulations and analytical solutions that study the tunneling-induced ground stress. This paper conducts a series of physical model tests to measure the stress state evolution of the surrounding soil during the tunnel advancing process. The ground compactness, as the most critical factor that determines the mechanical properties of sand, is the control variable in different groups of tests. The measurement results show that at the tunnel crown, the minor principal stress sigma 3, which is along the vertical direction, decreases to 0 kPa when the relative density (Dr) of the ground is 35% or 55%. Therefore, we can deduce that the sand above the crown collapses. When Dr = 80%, sigma 3 does not reach 0 kPa but its variation gradient is very fast. At the shoulder, the direction angles of three principal stresses are calculated to confirm the existence of the principal stress rotation during tunnel excavation. As the ground becomes denser, the degree of the principal stress rotation gradually decreases. According to the limited variation of the normal stress components and short stress paths at the springline, the loosened region is found to be concentrated near the excavation section, especially in dense ground. As a result, different measures should be taken to deal with the tunnel excavation problem in the ground with different compactness.

The transfer process of vertical stress of strata is affected by local soil arching effect, to address the limitation of differential soil layer method in overestimating the transferred stress, a method for calculating average vertical stress based on stress transfer ratio was proposed. This approach integrates numerical simulation results on the relationship between the rotation angle of principal stress and the average vertical compressive and shear stresses. Additionally, the shear stress distribution and the transmission behavior of vertical stress in both the equal settlement zone and the arching zone were verified. The results indicate that the stress transfer ratio can be used to define the boundary between the equal settlement plane and the soil arching zone of the tunnel. As the final stress transfer ratio increases, the path of principle stress gradually evolves into a closed arch trace, the proportion of transition before the peak of the average vertical stress curve decreases, while both the inflection point of the stress curve and the boundary of the equal settlement zone shift upward, and the transferred stress of strata with unit thickness increases accordingly. The transferred stress increases with gradual rotation of the principal stress, once the principal stress path forms a closed arch, the stress transfer function exhibits a sharp rise. The rate of change of the stress transfer ratio also increases in tandem with the rotation angle of the principal stress. These findings reveal the vertical stress transfer mechanism in the local soil arching zone and clarify the influence of the principal stress path on this process.

Further investigation into the progression of soil arching under the impact of noncentered tunnel is warranted. This study addresses this need by examining trapdoor models with varying vertical and horizontal spacings between the tunnel and the trapdoor through the discrete element method. The numerical model underwent calibration utilizing data from previous experiments. The results indicated that the soil arching ratio under the impact of noncentered tunnel exhibits four distinct stages: initial soil arching, maximum soil arching, load recovery, and ultimate stage, aligning with observations unaffected by tunnel presence. The minimal disparity in stress ratio within the stationary region was observed when the vertical spacing between the tunnel and the trapdoor ranges between 150 and 200 mm. Moreover, the disturbed area on the left part of the trapdoor extended significantly beyond the trapdoor width, with notably higher disturbance height compared to the right side. When the tunnel deviated from the centerline of the trapdoor, the stress enhancement on the right side was considerably greater compared to the left. Additionally, the displacement of the trapdoor resulted in a reduction of contact force anisotropy in the soil on the side more distant from the tunnel, while increasing it on the side closer to the tunnel.

Although universal in practical engineering, the soil arching effect induced by tunnel face unloading (TFU) in the unsaturated sandy ground (USG) hardly receives academic concerns for its complicacy. In this study, a physical model and a discrete element method (DEM) incorporating the interparticle capillary water force (ICWF) were established and verified. With the combination of experimental and numerical TFU, the intrinsic mechanism of soil arching effect in the USG was innovatively investigated from macroscale to mesoscale. The results indicate that the tunnel face limit support pressure in sandy ground decreases firstly, and then increases with the increase of saturation degree and its minimum value can be less than 22% of that in the dry sandy ground (DSG). Meanwhile, distinct from the global collapse in DSG, a self-stabilized soil arch emerges above the tunnel crown in USG and prevents the loosening zone from further development. With more effective stress transfer under the stronger soil arching effect, the cover-ratios of transition zone and weak deflection zone for the major principal stress in USG can decrease to 24% and increase to 47% respectively as compared to those in the DSG. Additionally, the coordinate number, weak contact proportion, porosity, and contact anisotropy can effectively reflect the meso-mechanical characteristics of soil arching effect in the USG. This work provides precious evidence for evaluating the tunnel face stability in the USG.

Determining earth pressure on jacked pipes is essential for ensuring lining safety and calculating jacking force, especially for deep-buried pipes. To better reflect the soil arching effect resulting from the excavation of rectangular jacked pipes and the distribution of the earth pressure on jacked pipes, we present an analytical solution for predicting the vertical earth pressure on deep-buried rectangular pipe jacking tunnels, incorporating the tunnelling-induced ground loss distribution. Our proposed analytical model consists of the upper multi-layer parabolic soil arch and the lower friction arch. The key parameters (i.e., width and height of friction arch B and height of parabolic soil arch H1) are determined according to the existing research, and an analytical solution for Kl is derived based on the distribution characteristics of the principal stress rotation angle. With consideration for the transition effect of the mechanical characteristics of the parabolic arch zone, an analytical solution for soil load transfer is derived. The prediction results of our analytical solution are compared with tests and simulation results to validate the effectiveness of the proposed analytical solution. Finally, the effects of different parameters on the soil pressure are discussed.

As urbanization accelerates, the demand for efficient underground infrastructure has grown, with rectangular tunnels gaining prominence due to their enhanced space utilization and construction efficiency. However, ensuring the stability of shallow rectangular tunnel faces in undrained clays presents significant challenges due to complex soil behaviors, including anisotropy and non-homogeneity. This study addresses these challenges by developing a novel failure mechanism within the kinematic approach of limit analysis, integrating soil arching effects alongside anisotropic and non-homogeneous undrained shear strength. The mechanism's analytical solutions are rigorously validated against finite element simulations using PLAXIS 3D and existing models, demonstrating superior accuracy. Key findings show that the proposed model improves predictive performance for critical support pressure, with relative differences as low as 5% for wide rectangular tunnels compared to numerical simulations. Results reveal that limit support pressure decreases with increasing non-homogeneity ratios and rises with higher anisotropy factors. However, both effects diminish in wider tunnels, where increasing width in soils with high non-homogeneity and low anisotropy factors significantly enhances stability. Practical implications of this study are substantial, offering design formulas and dimensionless coefficients for estimating critical face pressures in shallow rectangular tunnels. These tools enable engineers to account for soil anisotropy and non-homogeneity, optimizing design and ensuring safety in urban environments. Furthermore, the proposed model's applicability extends to circular tunnels, where it offers comparable accuracy. This study bridges a critical gap in understanding the stability of rectangular tunnels, providing a robust framework for tackling the challenges of modern urban construction.

The loose earth pressure in tunnels is closely related to the soil arching effect and the development of the loosening zone. Current methods overlook changes in the shape and position of the slip surface at different stages of the loosening zone, neglecting the relationship between these changes and principal stress rotation. An elliptical slip surface model has been developed to accurately capture variations in the shape and position of the slip surface as the loosening zone evolves. A lateral earth pressure coefficient for various inclinations of the slip surface was established to illustrate the relationship between the geometry of the slip surface and the rotation of principal stresses. Factors such as ground loss, soil arching effect, and elliptical slip surfaces, were integrated into the Terzaghi model, deriving and validating a numerical method for tunnel loose earth pressure. Parametric analysis targeting the volume loss ratio (VL) and cover-to-diameter ratio (C/D) revealed that linear, parabolic, and other slip surface forms presented are approximations of the elliptical slip surface at various stages. Loose earth pressure increases rapidly with C/D and then grows slowly but steadily. It decreases quickly with an increasing VL, then increases gradually and stabilizes.

Precisely evaluating the soil pressure above parallel tunnels is of paramount importance. In this study, the deformation characteristics of soil above dual trapdoors were analyzed firstly. A novel multi-arch model for calculating the distribution of the vertical earth pressure on deep-buried parallel tunnel was then proposed based on the limit equilibrium method. The height of the dual arch zone caused by the displacement of the dual trapdoors was calculated with consideration of internal friction angle of the soil, width of the trapdoors, spacing between the dual trapdoors, and elastic modulus of the soil. By comparing with numerical simulation results and existing theoretical calculation models that do not account for the interaction of soil arching effect, it is evident that the proposed model in this study adeptly predicts the vertical stress above the trapdoor. Additionally, it captures the characteristic of upwardly convex stress distribution above the trapdoor. The analysis of parameters conducted on the theoretical calculation model showed that the depth of the trapdoor and the internal friction angle of the soil have a substantial impact, whereas the expansion coefficient exerts a negligible effect on the soil arching ratio above the trapdoor.