# Numerical Simulation of Rock Mass Structure Effect on Tunnel Smooth Blasting Quality: A Case Study
## 3 Results and Discussions
### Cataclastic Structure Rock Mass  
Through single factor analysis, the influence curves of various factors of cataclastic structure could be obtained, as shown in Figure 14. The peripheral hole spacing had the most significant effect on the overbreak rate of smooth blasting. When the peripheral hole spacing increased from 40 cm to 50 cm, the overbreak rate of the tunnel decreased from 14.98% to 10.07%, with a decrease of 32.77%. However, when the peripheral hole spacing increased from 50 cm to 80 cm, the overbreak rate decreased by only 4.68%, which reflected that the overbreak rate decreased with the increasing peripheral eye spacing, and the decrease was slower. When the peripheral hole spacing was greater than 50 cm, its influence on the overbreak rate was relatively small. For cataclastic structure rock mass, the overbreak rate was generally serious when the peripheral hole spacing was less than 50 cm. Thus, the peripheral hole spacing should not be less than 50 cm. When the rock density increased from 1.5 g/cm\({}^{3}\) to 1.8 g/cm\({}^{3}\), the overbreak rate decreased from 14.91% to 14.27%, with a decrease of only 4.09%. However, when the rock density increased from 1.8 g/cm\({}^{3}\) to 2.1g/cm\({}^{3}\) and from 2.1 g/cm\({}^{3}\) to 2.4 g/cm\({}^{3}\), the reduction of overbreak rate reached 23.57% and 45.39%, respectively. When the rock density was less than 1.8 g/cm\({}^{3}\), the density had a limited influence on the blasting overbreak rate. When the density was greater than 1.8 g/cm\({}^{3}\), the overbreak rate decreased rapidly as the density increased. Therefore, for cataclastic structure rock mass, the density of less than 2.0 g/cm\({}^{3}\) had a great influence on smooth blasting overbreak. Thus, special attention should be paid to blasting design and construction. The influence of the \(Q\) classification index on smooth blasting overbreak was less than that of rock density. The curve showed that the overbreak rate decreased with the increase in \(Q\), and the decreasing range was relatively stable. In the  
Figure 13: Overbreak or underbreak rate of smooth blasting under different levels of each factor in the layered structure rock mass.  
cataclastic structure rock mass, the structural planes were extremely developed, and \(Q\) was a characterization method of the development degree of the structural plane. The smaller the \(Q\) was, the more fragmented the rock mass was, resulting in the overbreak rate increasing with the decrease in \(Q\).  
According to the main effect analysis of fuzzy mathematics theory, the maximum membership degree of the rock density, rock compressive strength, Q classification index, peripheral hole spacing, heading hole spacing, and the vertical spacing between the peripheral hole and the heading hole was \(\hat{F}_{\rho}\ =\ 0.272\), \(\hat{F}_{\sigma_{e}}\ =\ 0.221\), \(\hat{F}_{Q}\ =\ 0.261\), \(\hat{F}_{p}\ =\ 0.274\), \(\hat{F}_{H}\ =\ 0.221\), and \(\hat{F}_{S}\ =\ 0.232\), respectively. Given that \(\hat{F}_{p}>\hat{F}_{Q}>\hat{F}_{S}>\hat{F}_{\sigma_{e}}>\hat{F}_{H}\), the order of the influence weights of these six factors was peripheral hole spacing, rock density, Q classification index, the vertical spacing between the peripheral hole and the heading hole, rock compressive strength, and heading hole spacing. The maximum degree of membership of the peripheral hole spacing was 0.274, and the peripheral hole spacing was the most influential factor. For cataclastic structure rock mass, to reduce the overbreak rate in smooth blasting, the peripheral hole spacing should be strictly controlled, and the peripheral hole spacing should not be less than 50 cm. The maximum membership degree of the \(Q\) classification index was 0.261, with a large weight, indicating that the development degree of the structural plane had a great influence on smooth blasting. The more fragmented the rock mass was, the more prone it was to overbreak.