## 1 Introduction  
In underground engineering, such as tunnel excavation and mining engineering, blasting is an effective measure to break up rock mass. Although the application of blasting significantly improves the efficiency of underground cavern excavation, it causes damage to the surrounding rock. To reduce the damage of blasting to the surrounding rock, the blasting excavation design and construction technology need to be optimized. Therefore, the rock fracture process caused by blasting is characterized and classified. [PERSON] et al. [1] established a damage model of compact basalt and almond-shaped basalt to study the damage of dynamic load on basalt rock mass. [PERSON] et al. [2] established a split-Hopkinson pressure bar (SHPB) model to study the stress-strain relationship of rocks under dynamic loads, and a series of parameters affecting the dynamic mechanical properties of rocks were obtained. [PERSON] et al. [3] conducted field blasting tests by controlling blast hole spacings and charging methods and studied the design modes and blasting excavation construction technologies. [PERSON] et al. [4] used a triaxial blasting vibration waveform monitoring device to monitor the rock mass damage in the mining field and established a rock damage model for blasting design. However, the blasting excavation test has the disadvantages of a high safety risk, complicated operation, poor repeatability, and high cost. Recently, more and more scholarsare using numerical simulation to study blasting excavation. [PERSON] et al. [5] used a three-dimensional numerical simulation to study the fracturing effect of the surrounding rock under the excavation stress. [PERSON] et al. [6] studied the expansion process of the rock fracture propagation process during blasting excavation in the TASQ tunnel of the Aspo laboratory. [PERSON] et al. [7] used a finite-difference program (FLAC) to study the mechanical behavior of blast-damaged rock masses in shallow tunnels, and the results showed that the blast damage area can significantly induce boundary stress and affect the distribution and magnitude of ground deformation. [PERSON] et al. [8] proposed a mathematical model for the dynamic excavation response of a circular roadway under hydrostatic pressure and analyzed the dynamic response mechanism of the surrounding rock under different unloading rates and different unloading paths using PFC. [PERSON] et al. [9] used the LS-DYNA to simulate the rock damage evolution process under the dynamic stress redistribution and explosive loading and confirmed that the dynamic stress redistribution generates additional stress fluctuations, resulting in a larger rock damage area. [PERSON] et al. [10] introduced a new damage model in the LS-DYNA to study the effect of in situ stress distribution on the development of damage zones around deep-buried tunnels during the cutting blasting process. However, the above research rarely considers the near-field fracture evolution of the tunnel surrounding rock. The finite-discrete element method (FDEM) proposed by [PERSON] [11; 12] has been successfully used to model the transition from continuum to discontinuity and developed the open-source program Y2D. The FDEM absorbs the advantages of the explicit finite element method for solving deformation and stress, the advantages of the discrete element method for dealing with contact, and the advantages of the cohesive element model for simulating fracture. In the FDEM, the solution domain is divided into solid finite element meshes, and initial zero thickness joint elements that are similar to cohesion elements are inserted into the boundaries of the solid elements. In addition, the initiation and propagation of cracks are simulated by the fracture of joint elements. The deformation and stress of the continuum are characterized by the deformation of the solid elements and the bonding effect of the unbroken joint elements.