###### Abstract  
Conventional bolts frequently fail under large deformations due to stress concentration in soft rock tunnels. In contrast, yielding bolts incorporate energy-absorbing mechanisms to sustain controlled plastic deformation. This study employed FLAC3D to numerically investigate the pull-out, shear, and bending behaviors of yielding bolts, evaluating their support effectiveness in soft rock tunnels. Three-dimensional finite difference models incorporating nonlinear coupling springs and the Mohr-Coulomb criterion were developed to simulate bolt-rock interactions under multifactorial loading. Validation against experimental pull-out tests and field measurements confirmed the model accuracy. Under pull-out loading, the axial forces in yielding bolts decreased more rapidly along the bolt length, reducing stress concentration at the head. The central position of the maximum load-bearing capacity in conventional bolts fractured under tension, resulting in an hourglass-shaped axial force distribution. Conversely, the yielding bolts maintained yield strength for an extended period after reaching it, exhibiting a spindle-shaped axial force distribution. Parametric analyses reveal that bolt spacing exerts a greater influence on support effectiveness than length. This study bridges critical gaps in understanding yielding bolt behavior under combined loading and provides a validated framework for optimizing energy-absorbing support systems in soft rock tunnels. Y 2025 13  
bolts, which integrate energy-absorbing mechanisms to sustain controlled plastic deformation without losing load-bearing capacity [10]. Despite their growing application, the mechanical behavior of yielding bolts under combined loading regimes--specifically pull-out, shear, and bending--and their interaction with soft rock masses remain insufficiently characterized [11; 12]. Addressing these knowledge gaps is pivotal for optimizing yielding bolt design and validating their efficacy in real-world tunneling scenarios, particularly in geotechnically challenging environments. While experimental studies on yielding bolts have demonstrated their superior elongation capacity compared to conventional systems [13], most of the research has focused on simplified laboratory pull-out tests, leaving critical questions unanswered. For instance, the shear resistance of yielding bolts has received limited attention [14; 15]. Similarly, the bending behavior of these bolts under lateral loads, such as those induced by asymmetrical ground pressures, remains poorly understood [16]. Furthermore, existing studies often neglect the holistic performance of yielding bolts in full-scale tunnel models, where complex stress paths, rock-bolt coupling effects, and time-dependent deformation interplay [17]. These limitations underscore the need for advanced numerical frameworks capable of simulating multifactorial loading conditions and providing insights into bolt-rock interactions at both local and global scales. Numerical modeling has emerged as a powerful tool for analyzing the nonlinear behavior of support systems in soft rock tunnels [18; 19; 20; 21]. The finite difference method, implemented in software such as FLAC3D, is particularly suited for this purpose due to its ability to handle large deformations, interface slip, and elastoplastic material responses [22; 23; 24]. Prior studies by [PERSON] et al. [25] and [PERSON] and [PERSON] [26] validated the capability of FLAC3D to replicate the pull-out and shear tests of conventional bolts, establishing its credibility for simulating bolt-rock interactions. [PERSON] et al. [27] employed numerical simulation methods to analyze the influence of boundary conditions on the shear behavior of rock joints. [PERSON] et al. [28] used Flac3D to study the development law of interface for geotechnical prestressed anchorage bolt. [PERSON] et al. [29] revealed the shear characteristics of the bolt-gravit interface under cyclic shear loading.