To elucidate the micromechanical origins of the macroscopic anisotropic behavior of granular materials, this study develops a micromechanically based elastoplastic constitutive model for sand. First, anchored in the static equilibrium hypothesis and granular micromechanics theory, a true stress tensor is introduced to characterize the authentic inter-particle contact forces. Serving as a coupled variable of the macroscopic stress and the microscopic fabric tensor, this formulation not only quantifies the directional distribution of the contact network but also enables the mapping of anisotropic yielding and deformation analyses into an equivalent isotropic true stress space. Subsequently, a comprehensive constitutive framework is established by integrating critical state theory, an anisotropic fabric evolution law, and an energy-based stress–dilatancy relationship that explicitly accounts for the evolution mechanism of the microscopic coordination number. The physical interpretation, calibration procedure, and sensitivity analysis of the model parameters are also presented. The predictive capability of the model is rigorously validated against conventional triaxial tests on Ottawa sand, true triaxial numerical simulations, and experimental data for Toyoura sand with inherent anisotropy. The comparisons demonstrate that the model accurately captures not only the stress–strain response and volumetric deformation under conventional loading but also the strength dependency on loading direction and mechanical characteristics under complex stress paths, substantiating the validity and universality of the proposed micromechanical approach.

This study aims to assess and select shield tunnel segment configurations and assembly angles based on the characteristics of circumferential internal force distribution. Based on the multi-hinged circular ring method and considering the diversity of assembly angles and segment configurations in practical engineering, a fundamental equation is established to calculate the contact forces at the longitudinal joints of a single shield segmental ring under arbitrary segment configurations and assembly angles. In addition, formulas for calculating internal forces are derived, and the corresponding coefficient matrix and constant vector are obtained, which significantly simplifies the process of solving the equation. Results from an actual project show that the calculated internal-force distributions are consistent with the expected mechanical response, while the calculated longitudinal-joint contact pressures show reasonable agreement with field measurements, supporting the reliability of the proposed method under the investigated engineering conditions. For the investigated circular segmental ring, the segment configuration and assembly angle significantly affect the distribution of internal forces. Moreover, appropriate configurations and assembly angles can effectively reduce bending moments and shear forces within the segments. When the segment configuration and assembly angle are fixed, external loads have a greater impact on the magnitudes of internal forces but less influence on their distribution. The selection of the segment assembly angle should be based on specific engineering objectives, such as structural performance and joint waterproofing requirements. The proposed method provides a basis for the assessment and selection of segment configurations and assembly angles, as well as for the design of longitudinal-joint waterproofing measures in practical engineering.