## 4 Modeling and Parameters of Numerical Simulations  
In order to obtain the damage distribution characteristics of slit charge blasting in the layered rock mass, numerical simulation analysis is carried out using the LS-DYNA program. LS-DYNA program is capable of solving a wide range of nonlinear problems, including material nonlinearity, geometric nonlinearity, and contact nonlinearity. This program is extensively utilized in the fields of high-speed impact, blasting engineering, seismic construction, and other related areas. The primary calculation methods employed by the LS-DYNA program include the Lagrange algorithm, the Euler algorithm, ALE (Arbitrary Lagrange-Euler) algorithm, and the Smoothed Particle Hydrodynamics (SPH) algorithm [24; 25]. With reference to the relevant parameters of the model experiment, the numerical simulation model shown in Figure 9 is established. The numerical simulation adopts a quarter-symmetrical modeling method, which not only facilitates the comparative analysis of damage characteristics in different directions but also reduces the number of elements and increases the computational efficiency. The quarter model shown in Figure 9 is 150 cm in length and width and 56 cm in height. The model consists of 14 layers of rock mass, each with a thickness of 4 cm. In the numerical model, the diameter of the borehole is 5 cm, and the outer and inner diameters of the slit charge are 5 cm and 3 cm, respectively. Similar to the model experiment, the positions of the slit charge corresponding to the first layer and the fourteenth layer of rock mass are not charged, the explosive is detonated from the second layer of the rock mass and propagated to the direction of the fourteenth layer of the rock mass.  
Figure 8: Changing curve of the damage value with the layer number.  
Figure 9: Schematic diagram of numerical simulation modeling.  
In the numerical simulation, the constitutive model of the rock mass is the RHT model, which is a constitutive model that can characterize the damage characteristics of rock materials under impact and blast loads. The constitutive model introduces the influence of the third invariant J3 of the deviatoric stress tensor on the shape of the failure surface, and J3 can qualitatively determine the strain type and stress state of the material. Furthermore, the strength of the rock material increases under dynamic loading due to the strain rate effect. The RHT model describes the strain rate effects of materials under compression and tension by introducing a dynamic strain rate enhancement factor. The damage variable D in this model is the ratio of the cumulative equivalent plastic strain increment to the final failure equivalent plastic strain. The main parameters of the rock material in the numerical simulation are shown in Table 3.  
In the numerical simulation, the high-energy explosive model is used for the explosive, and the JWL equation is introduced to describe the relationship between pressure and volume during the blasting process. The main parameters of the explosive material in the numerical simulation are shown in Table 4.  
In order to simplify the calculation, the contact property of the layered rock mass is defined as automatic surface-surface contact, and the fluid-structure coupling algorithm is used between the explosive and the rock mass. Under the action of the blasting load, the rock mass element around the borehole will be greatly deformed, which affects the convergence of numerical simulation calculation. Therefore, by introducing the *MAT_ADD_EROSION command to control the failure of the rock mass element with large deformations, the failure strain of the rock mass element is set to 0.2.