To explore the damage and failure mechanisms of shield tunnel segments in soft and hard strata under overload condition, a comprehensive model encompassing segments, bolts, reinforcing steel, and soil was established based on a tunnel engineering project. The reliability of the model was verified by comparing the internal force change curves from experiments with the numerical simulation results. A three-dimensional discontinuous contact model for soil-segment interaction was constructed using the stratum structure method and incorporating the Concrete Damage Plasticity (CDP) constitutive model, which takes into account the nonlinearity of segment structures as well as the yielding, hardening, and softening behaviors of the embedded reinforcements. The analysis compared the force and damage mechanisms of segment structures in different strata, lateral pressure coefficients, and positions of top blocks. The results showed that the overall rigidity of the shield tunnel structure is enhanced in hard soil layers, resulting in better-controlled deformation. As the lateral pressure coefficient increases, both the ellipticity of the segments and the stress on the bolts decrease, delaying the occurrence time of maximum damage in the segment structures and enhancing their load-bearing capacity and stability. The position of the top blocks affects the initial damage location of the segments. Damage occurs earliest and is most severe when the block is at the crown, while it is minimal in terms of both magnitude and distribution when the block is at 90° at the arch waist.