## 5 Numerical Simulation of Blasting Hole Network Parameters
### Numerical Simulation Results
In the whole propagation process, compared with other borehole apertures, a 120 mm delay evolved into seismic waves, and its energy attenuation rate is slower than other borehole apertures. The fastest energy attenuation rate is 130 mm borehole aperture. The stress state of rock mass under blasting load is very complex. In order to study whether the cracks formed between the two boreholes are penetrating or not and whether the rock mass is damaged, the \(Y\)-axis stress of the rock mass unit connected with the borehole is taken as the basis for consideration. The maximum tensile strength of the rock used in the model is 3.5 MPa. If the maximum stress of the \(Y\)-axis direction of the rock mass unit is greater than the maximum tensile strength of the rock, it is considered that  
Figure 13: A 90 mm aperture 630 mm hole spacing stress wave propagation nephogram. (**a**) 0.5 ms. (**b**) 1 ms. (**c**) 2 ms. (**d**) 3 ms. (**e**) 4 ms.  
the cracks formed between the two boreholes are penetrating. The Y-direction stress-time history of four observation points A, B, C and D in each working condition is shown in Figure 14.  
Taking the 90 mm aperture as an example, the observation point curve is shown in Figure 14a. When 0 us, the two holes begin to detonate, and the stress wave generated by the explosion extends outward. The stress wave propagates to the observation point D, C, B and A at 136.85 us, 846.15 us, 1898.34 us and 2395.08 us, respectively, and it causes the stress change. Then, the stress wave and the pressure generated by the explosion gas work together. At 326.41 us, 1371.58 us, 2129.37 us, and 2962.18 us, respectively, the Y-direction stress peak is reached. When the stress wave propagates to the bottom of the blockage, part of the wave will produce reflection phenomenon and propagate back in the form of an unloading wave. After C, B and A observation points in turn, the Y-direction stress secondary peak appears at C and B points. The peak fluctuation of A point is small because the energy of the unloading wave will be accompanied by secondary attenuation in the process of propagation, and the energy has been attenuated to about 1/3 when propagating to the A point. It can be seen from Figure 14a-e that with the attenuation of stress wave propagation energy, the Y-direction stress of observation points B, C and D is basically stable between 2.3 and 3.5 MPa, and the Y-direction stress of observation point A is basically stable between \(-\)1.3 and 1.2 MPa. It can be seen from Figure 15a-e that with the increase in the spacing of blast holes, the peak stress in the Y direction of each measuring point also decreases, and the minimum stress appears near the observation point A. When the stress is greater than 3.5 MPa of the maximum tensile strength of the rock, the rock cracks and begins to damage. The peak stress in the Y direction of the observation point A in each working condition is less than 3.5 MPa and generally shows a downward trend, and the rock mass near it fails to crack. The B, C and D observation points of 90-130 mm aperture under different working conditions occurred rock cracking at 7-9 times, 7-9 times, 7-10 times, 7-11 times and 7-11 times hole spacing, respectively. The cracks of the two boreholes were interconnected. In addition to the above working conditions, only the stress wave was transmitted to the  
Figure 14: Y-direction stress–time history curves of each aperture and its 7 times aperture distance. (**a**) 90 mm aperture. (**b**) 100 mm aperture. (**c**) 110 mm aperture. (**d**) 120 mm aperture. (**e**) 130 mm aperture. corresponding area in other working conditions, but the peak stress in the Y direction was less than the dynamic tensile strength of the rock, and these conditions were only likely to crack at the superposition position of the stress wave, and the cracks of the two boreholes were not penetrated. It is possible that the stress wave propagates more energy dissipation and the stress superposition effect is weakened under the condition of large hole spacing.