During layered tunnel excavation, there is a complex three-dimensional spatial coupling relationship among bedding planes, tunnel contours, and stress directions, resulting in significant complex evolutionary characteristics of tunnel failure. Extrusion-based cementitious 3D printing technology offers advantages such as rock-like properties, rapid fabrication, low variability, and low cost. In this study, circular diversion tunnel models with different bedding orientations were fabricated using extrusion-based cementitious 3D printing. Overload failure tests and numerical simulations were conducted to analyze the mechanical characteristics and crack evolution mechanisms of layered circular tunnels under overload conditions. Results indicate that bedding orientation significantly influences the mechanical performance of layered tunnels. The peak strength of horizontal layered tunnels is higher than that of vertical ones. Bedding orientation primarily governs crack propagation paths. In horizontal bedding, cracks predominantly penetrate the layers, whereas in vertical bedding, cracks tend to propagate along weak bedding interfaces. For both orientations, crack initiation occurs at the tunnel crown and invert. Furthermore, horizontal layered tunnels exhibit a tensile-shear composite failure mode with matrix-penetrating cracks. In contrast, vertical layered tunnels show tensile failure along the bedding planes. These findings provide theoretical guidance for the excavation and support design of layered tunnels in stratified rock masses.