## 5 Case Study
### Results and Discussion  
Figure 10a is a three-dimensional blasting damage diagram of surrounding rock when \(d=1\) m. Figure 10b is cross-section diagram of surrounding rock blasting damage when \(d=1\) m. \(d\) is the spacing between the box culvert and the tunnel. From Figure 10a,b, it can be noted that the thickness of blasting-damaged rock beneath the box culvert with \(D>0.9\) is approximately 0.5 m; the thickness of blasting-damaged rock overlying the tunnel with \(D>0.8\) is approximately 20-22 cm. From Figure 10a, it can be noted that the thickness of the blasting-damaged rock between the box culvert and the tunnel with \(D<0.7\) is less than 30 cm. From Figure 10b, it can be noted that the thickness of the surrounding rock between the box culvert and the tunnel with \(D<0.7\) is approximately 20 cm; the thickness of the surrounding rock between the box culvert and the tunnel with \(D\geq 0.5\) is 1.0 m.  
Figure 11a is three-dimensional blasting damage diagram of surrounding rock when \(d=2\) m. Figure 11b is cross-section diagram of surrounding rock blasting damage when \(d=2\) m.  
Figure 10: Blasting damage diagram of surrounding rock (\(d=1\) m). (**a**) three-dimensional blasting damage diagram. (**b**) cross-section blasting damage diagram. From Figure 11a,b, it can be noted that the thickness of blasting-damaged surrounding rock beneath the box culvert with \(D>0.9\), is less than 15 cm, located from 1.2 m to 1.35 m beneath the box culvert. The thickness of blasting-damaged surrounding rock beneath the box culvert with \(D>0.7\), is less than 45 cm, located from 0.9 m to 1.35 m beneath the box culvert (see in Figure 11a). The thickness of blasting-damaged surrounding rock overlying the tunnel with \(D<0.6\), is approximately 60 cm (see in Figure 11a). The thickness of blasting-damaged surrounding rock beneath the box culvert with \(D\leq 0.5\), is more than 55 cm (see in Figure 11a). From Figure 11b, it can be noted that the thickness of blasting-damaged surrounding rock beneath the box culvert with \(D>0.8\), is less than 20 cm, located from 1.2 m to 1.4 m beneath the box culvert. The thickness of blasting-damaged surrounding rock overlying the tunnel with \(D\leq 0.5\), is more than 55 cm (see in Figure 11b). Comparing Figure 10a with Figure 11a, it can be found that the blasting damage range of surrounding rock and blasting damage degree of surrounding rock both very significantly reduce as the spacing between the box culvert and the tunnel increases from 1.0 m to 2.0 m. In addition, blasting damage of surrounding rock exists the concentrated phenomenon beneath the box culvert when the spacing between the box culvert and the tunnel is 1.0 m.  
Figure 12a is the three-dimensional blasting damage diagram of surrounding rock when \(d=3.0\) m. Figure 12b is a cross-section diagram of surrounding rock blasting damage when \(d=3.0\) m.  
From Figure 12a,b, it can be noted that the thickness of blasting-damaged surrounding rock beneath the box culvert with \(D<0.5\), is more than 2.35 m. The thickness of blasting-damaged surrounding rock beneath the box culvert with \(D=0.5\sim 0.7\) is 0.65 m, located from 0.65 m to 1.3 m overlying the tunnel (see in Figure 12a,b). Figure 13a is three-dimensional blasting damage diagram of surrounding rock when \(d=4.0\) m. Figure 13b is cross-section diagram of surrounding rock blasting damage when \(d=4.0\) m.  
From Figure 13a,b, it can be noted that the thickness of blasting-damaged surrounding rock beneath the box culvert with \(D<0.5\), is more than 3.7 m. The thickness of blasting-damaged surrounding rock beneath the box culvert with \(D=0.5\sim 0.7\) is 0.3 m, located from 0.45 m to 0.75 m overlying the tunnel (see in Figure 13a,b). Figure 12: Blasting damage diagram of surrounding rock (\(d=3\) m). (**a**) three-dimensional blasting damage diagram. (**b**) cross-section blasting damage diagram.