## 1 Introduction
However, it falls short in accurately reflecting the elastic-plastic behavior of continuous media, such as the response of anchor rods to stress [25]. Therefore, many researchers have combined the advantages of these two methods by coupling FEM-DEM to provide a solution to the above mentioned problems. [PERSON] et al. [32] established a numerical model of anchored fissured rock mass by coupling FEM and DEM, and investigated the internal stress evolution in the sample and the stress distribution in the anchor under the anchoring action. However, for natural rock materials with a crystalline structure, such as granite, the complexity of their internal mineral composition and structure means that using a homogeneous model to simulate granite materials has certain limitations. Currently, for the numerical modeling of granite materials, the grain-based model (GBM) has become the choice of many scholars [33; 34]. [PERSON] et al. [35; 36] were the first to establish a GBM based on the particle flow code (PFC). The PFC-GBM is capable not only of reproducing the interactions between crystals but also of simulating the internal mechanical behavior of mineral particles. In recent years, numerous scholars have improved upon the PFC-GBM and applied it to validate various indoor tests and to analyze the related mechanisms [37; 38; 39]. When rock materials are subjected to external loads, localized stress concentrations can lead to the destruction and fracturing of particles and bonds within the material, culminating in macroscopic failure. However, both the theoretical analysis and traditional indoor experimental methods fall short in capturing this macroscopic process. The force chain network (FCN) model offers a valuable perspective. It represents a network of interwoven force chains within granular materials. According to granular mechanics, under external loads, particles within the granular system are pressed against each other, creating a network known as the connection network of granular materials. These contact paths constitute the force chains and the overall force chain network. This network allows for the investigation of damage and fractures within the granular particles and their bonds in the rock material. Currently, the force chain network is widely used in geotechnical discrete element numerical simulation studies and is considered as an important source of mechanical information in the microscopic perspective of geotechnics. In 2002, [PERSON] et al. [40] simulated a straight shear test in geotechnics using DEM to investigate the particle morphology and force chain distribution. In 2020, [PERSON] et al. [41] used DEM to study the quasi-static behavior under active earth pressure conditions, and compared with the results of photo-elastic tests to successfully predict the overall structure of the force chain network and its characteristics. [PERSON] et al. [40] utilized the discrete element method (DEM) to simulate the direct shear test in soil mechanics, investigating the effects of particle shape and force chain distribution. In 2023, [PERSON] et al. [42] investigated the evolution and distribution characteristics of the internal contact force in samples with different particle size gradations. In summary, the force chain network is a crucial indicator for elucidating the shifts in the mechanical behavior of rock materials. It serves as a vital research instrument for dissecting the deformation and rupture processes of rock materials under load from a granular perspective. Consequently, examining the mechanical response of the fractured and anchored rock mass through the lens of the force chain network is imperative. To provide a scientific basis for the design and safety assessment of underground rock engineering, a combination of laboratory experiments and numerical simulations is employed, focusing on unanchored and anchored granite samples to capture their mechanical behavior during uniaxial compression tests.