## 3 Numerical Simulation of Compression Tests on Anchored Rock Mass  
### Determination of Computation Schemes and Microscopic Parameters  
Fully-grounded bolts exert a good anchoring effect on rock masses under different conditions, while the applicable bolt diameter and length differ across rock conditions, so bolts also have different mechanical properties. In view of this, influences of the properties of bolt support (length and diameter) and rock mass (strength and fracture angle) on the mechanical properties of bolt supports were mainly investigated. Moreover, analysis was performed from two aspects: stress distribution and anchorage force. The anchored rock mass is damaged, and fractures occur constantly in the compression process, so discrete element software PFC2D suitable for simulating rock fracturing was used for the computational simulation of compression tests on an anchored rock mass [35; 36]. It should be noted that many tests related to bolts, such as pullout tests on bolts and shear tests of anchored rock mass, etc., are three-dimensional problems. However, in PFC calculation, the calculation time of three-dimensional models is very long, which makes many scholars use two-dimensional models for research. Therefore, the two-dimensional model was also used for this study [37; 38]. Due to the correlation of computation time with the model size and the number of particles, to improve the computation efficiency and accuracy, the dimensions of surrounding rocks were set to be 300 mm \(\times\) 250 mm; the bolt  
Figure 2: Schematic representations of tests. (**a**) Pullout tests on bolts; (**b**) Compression tests on anchored rock mass. length was set to 80 mm, 130 mm, and 180 mm, and the bolt diameter was 12 mm, 16 mm, and 20 mm. The rock mass was classified into three types: soft, relatively hard, and hard rock masses. The fracture angle (angle between a fracture and a bolt) was set to be 90\({}^{\circ}\), 60\({}^{\circ}\), 45\({}^{\circ}\), and 30\({}^{\circ}\). The specific computation schemes are listed in Table 1, in which Scheme 1 is the control group. As the current research is not based on a specific project, macroscopic mechanical properties of the grouts, bolts, and bearing plates were all determined through experiments conducted by [PERSON] et al. [29]. The grouts were cement mortar; bolts were reinforcing steel bars; bearing plates were steel plates. Approximate values were taken for the macroscopic mechanical properties of the three types of surrounding rocks according to the classification index of the rock mass. To obtain those microscopic parameters needed for PFC computation, the macroscopic mechanical parameters need to be calibrated. At first, multiple samples of numerical models were generated in PFC, and uniaxial compression tests and Brazilian split tests were conducted. Then, parameters were adjusted using the trial-and-error method, so that the macroscopic mechanical parameters obtained via numerical simulation are approximated to the real macroscopic parameters of various materials. Owing to the large ratio of compressive strength to the tensile strength of a rock mass, to simulate such properties of rock while simulating the hardness and brittleness of grouts at the same time, the flat-joint contact model (FJM) was selected [39; 40]. The macroscopic mechanical parameters of various materials and those in the numerical simulation are listed in Table 2. Microscopic mechanical parameters of various materials are summarized in Table 3.