Fabric anisotropy significantly influences the mechanical behavior of sandy soils, potentially resulting in diverse failure patterns during shield tunneling owing to insufficient support pressure. In this paper, a set of specimens with bedding angles (alpha\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha$$\end{document}) and an isotropic specimen are well generated to simulate active failure at the tunnel face using DEM. The evolving failure of the soil in distinct alpha\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha$$\end{document} are scrutinized, and ground settlement is further explored. Furthermore, microscopic information is juxtaposed to systematically elucidate the influence of alpha\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha$$\end{document} on failure patterns at a microscopic level. Macroscopic findings reveal that, aside from specimens with alpha\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha$$\end{document} = 0 degrees and 90 degrees, particle displacement experiences deflection as it extends toward the ground surface in other specimens. However, this deflection behavior is only noticeable under conditions of large deformation. Additionally, across all specimens, the maximum displacement of the ground surface is observed in those with alpha\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha$$\end{document} = 90 degrees, while the minimum value is noted in specimens with alpha\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha$$\end{document} = 45 degrees. Notably, considerable particle rotation occurs within the shear face. However, the deflection behavior has not been found in specimens with alpha\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha$$\end{document} = 0 degrees and 90 degrees. Similarly, in specimens with these two specimens, there is no noteworthy deflection observed in the principal direction of contact normal.

This paper addresses stability challenges at excavation faces in shield tunneling through water-rich soil-rock formations, particularly focusing on partial failure caused by significant strength differences between soil and rock layers. A three-dimensional discrete rotational failure mechanism model is developed under the limit analysis upper-bound theorem, considering the influence of pore water pressure. This model leads to a novel method for calculating ultimate support pressure in complex strata, with its reliability confirmed through comparison with existing solutions. Key findings reveal a roughly linear positive correlation between soil layer proportion, water level, soil saturation weight, and ultimate support pressure. Conversely, cohesion, tunnel depth and friction angle demonstrate an inverse correlation. Notably, the relationship between soil layer proportion and ultimate support pressure exhibits significant nonlinearity. Cohesion and water level exert the most significant effects on ultimate support pressure, while the impact of soil layer proportion is notably complex. Additionally, a normalized design method is established using tunnel diameter and soil saturation weight, supported by design charts for varying normalized cohesion, normalized water level, and friction angles. A detailed example of a classic case is provided to illustrate the use of these design charts, aiding practical engineering applications.