## 1 Introduction  
Shale, a widely distributed sedimentary rock, contains abundant oil and gas resources and is a key source of clean energy [1, 2, 3, 4, 5, 6]. Currently, hydraulic fracturing technology is commonly employed in shale gas development, where fracturing fluid is injected to create a continuous fracture network within the shale, allowing shale gas to escape from the reservoir and flow into the wellbore. The extent of the fracture network's development directly impacts the efficiency of shale gas extraction, making it crucial to understand the formation and evolution of fractures in shale under stress [7, 8]. However, natural fractures, pores, and other defects are prevalent within shale, with these structural weaknesses often exhibiting high levels of damage [9, 10, 11]. Additionally, the layered structure formed during sedimentation imparts high brittleness and notable anisotropy to shale. The angle differences in weak bedding, in particular, significantly affect its mechanical properties, crack initiation and propagation, and failure modes. These characteristics complicate shale'sstability and fracture behavior in engineering applications, making it more challenging than isotropic rocks. Therefore, in-depth research on the formation mechanisms of complex fracture networks during fracturing and the anisotropic effects of bedding on mechanical behavior and failure modes is of great practical significance for optimizing fracturing operations and improving shale gas extraction efficiency. When stored underground, shale is subjected to a complex stress state, prompting extensive research on its anisotropic fracture characteristics. [PERSON] et al. [12] investigated the anisotropic failure modes of Xiangxi shale through uniaxial compression tests, while [PERSON] et al. [13] examined the uniaxial compression behavior of shale soaked in fracturing fluids with different pH values, analyzing its mechanical properties and failure characteristics. [PERSON] et al. [14] and [PERSON] et al. [15] studied the effects of bedding inclination and confining pressure on the brittleness of Longmaxi outcrop shale through conventional triaxial tests. They proposed a new brittleness index for assessing the relationship between shale brittleness and failure modes. Additionally, research on shale tensile properties has gained significant attention. [PERSON] et al. [16] combined the semi-circular disk test with digital image processing to quantify the fracture process zone of shale and evaluate its fracture toughness. [PERSON] et al. [17] proposed four distinct tensile failure modes for shale and established corresponding criteria for evaluating tensile strength. [PERSON] et al. [18] conducted Brazilian disc and uniaxial triaxial tests to investigate the failure modes of shale under varying stress states. Further studies have performed direct shear and creep tests [19; 20] and uniaxial compression tests considering strain rate effects [21], providing deeper insights into shale's anisotropic characteristics under different conditions. In addition to conventional rock materials, [PERSON] et al. [22] examined the anisotropy of cast-like layered rock materials, finding that under triaxial loading, the crack morphology of these materials closely resembled that of shale. With emerging technologies, 3D printing has also been applied in rock mechanics. [PERSON] et al. [23] and [PERSON] et al. [24] conducted uniaxial compression tests on 3D-printed layered gypsum rock, revealing a similar strength change pattern to natural rock. These findings suggest that the anisotropy of shale primarily arises from its bedding structure. The experimental results demonstrate that the weak bedding defects formed during sedimentation induce significant mechanical differences in shale in various directions. However, most existing studies focus on macroscopic destruction phenomena.