## 3 Test Results and Analysis
### The Description of the Macroscopic Damage Characteristics of the Structures  
The expanded photograph of the arch and straight wall of the test sections after explosion is obtained by means of segmental shooting, cropping and combination, as shown in Figure 8. From left to right, the test sections A, B and C are shown in the figure, in which the test section A is located at the mouth of the structure. By collecting and analyzing data of the test sections suffering the explosion load, the macroscopic damage characteristics of the three different types of structures are described. The macroscopic damage phenomenon of the internal structure of test section A after enduring the explosion load is shown in Figure 9a. The width of the crack in the middle of the vault is about 5 mm, and completely connects with the bottom of the explosion cavity. However, the crack in the vault is not a continuous straight line. The crack extends from the prefabricated bolt hole to the vault. The reason is that the high-performance reinforced concrete test section is composed of the two precast sections. Although the bolt hole has \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Measuring**} & \multicolumn{2}{c}{**Peak Pressures (MPa)**} & \multicolumn{2}{c}{**Duration of Positive Pressure (ms)**} \\ \cline{2-5}  & **Measured Value** & **Mean Value** & **Measured Value** & **Mean Value** \\ \hline J1 & 26.74 & 24.37 & 12.27 & 11.84 \\ J2 & 24.72 & 24.37 & 12.75 & 11.84 \\ J3 & 23.11 & 24.37 & 11.44 & 11.84 \\ J4 & 22.91 & 24.37 & 10.91 & 11.84 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The measured results at the bottom of the explosion cavity. Figure 7: The measured pressure time travel curves at the bottom of the explosion cavity: (**a**) measuring point J1; (**b**) measuring point J2; (**c**) measuring point J3; (**d**) measuring point J4. The high-performance reinforced concrete on the inner surface of the left and right arch feet is slightly damaged, and the left and right arch spring appears some discontinuous cracks along the thickness direction, as shown in Figure 9b,c. According to the analysis, under the condition of plane explosion wave load, the high-performance reinforced concrete firstly occurs a slight damage at the arch spring, which increases the bending moment of the vault. Under the action of reflected tensile wave, the stress characteristics of the arch change results in the appearance of an opening crack mode in the vault. Furthermore, there is no obvious damage to the straight walls on both sides. There is only a long thin crack with length 1.1 mm and 70 cm away from away from the left straight wall on the floor, which is caused by the foundation reaction and coincided with the damage position of the bottom of the explosion cavity, as shown in Figure 9d. The crack at the bottom of the explosion cavity deflects to the left, and the downward load is slightly larger. The macroscopic damage of the C30 reinforced concrete test section is shown in Figure 10, and there are no obvious cracks on the vault. Near the direction of the entrance, four small cracks with the width about 1 mm appears on both sides of the arch waist. The crack on the right spandrel extends about 90 cm from the end face of the structure. The left spandrel almost runs through the test section, especially in the second half of the test section, with the concrete shear breaking and falling, and the crack runs through the outer surface of the structure. The left arch spring appears an extrusion fracture zone, part of the concrete fall off, and there is an empty drum sound when the part that does not fall off is knocked, as shown in Figure 10a. The right arch spring emerges an extrusion fracture zone within 1 m of the inner end face, with a width of 20 cm, and the concrete is crushed and dropped, as shown in Figure 10b. The left straight wall only produces a vertical micro-crack at 125 cm away from the outer end of the structure.