## 2 Test Design and Program
### Test Program  
The explosion crater size of the plane charge loading test is 9.0 m \(\times\) 5.5 m \(\times\) 2.0 m, in which the height of the explosion cavity is 0.5 m. By adopting the high-pressure plane charge loading test technique, 384 kg of rock expanded ammonium nitrate explosive is designed to be arranged in the explosion cavity in the three layers. The head and tail of a single rock expanded ammonium nitrate explosive roll are connected to form a cord-like explosive roll with the same length as the explosion cavity. The cord-like explosive roll is evenly distributed in the explosion cavity in the three layers. All the cord-like explosive rolls are connected by the detonating fuse to form the initiation network, which is connected to the electric detonator. Each row of charge is detonated by detonating fuse to form a wire detonation. The cord-like charge of each layer is detonated at multiple points at the same time. The combination of line detonating and multi-point detonating ensures the formation of a quasi-plane blast wave after the explosion of each layer of explosives in the explosion cavity. The schematic of the high-pressure plane charge loading test is shown in Figure 1. The design value of the tamped backfill layer at the upper part of the formwork is 5 m, and the overburden density is about 1600 kg/m\({}^{3}\). Figure 1: The schematic of the high-pressure plane charge loading test. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Material**} & **P.O42.5** & **Water to** & **Quartz** & **Quartz** & **Microsilica** & **Fly ash** & **Water-** & **Steel Fiber** & **Nanometer** \\  & **Cement** & **Binder** & **Sand** & **Powder** & **Microsilica** & **Fly ash** & **Reducing** & **Mineral** \\  & **Cement** & **Ratio** & **Sand** & **Powder** & **Admixture** & **Sand** & **Powder** \\ \hline Mass ratio & 1.0 & 0.16 & 1.1 & 0.3 & 0.2 & 0.1 & 1.5\% & 1\% & 1.5\%NS + 3\%NC \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The mix design of high-performance concrete. The test tunnel is 0.5 m away from the bottom of the explosion cavity. The total length of the test tunnel is 9 m. A total of 3 test sections are designed in the tunnel. Three test sections A, B and C are arranged from the structure mouth inward. Each test section is 3 m. The engineering layout of the structural test sections is shown in Figure 2. The test section A is a high-performance reinforced concrete prefabricated structure, which is constructed by way of factory prefabrication and on-site assembly. To ensure the strength of the high-performance reinforced concrete structure and convenience of transportation, it is prefabricated in two sections with the length of each section 1.5 m and thickness 0.3 m, and the two prefabricated structures are connected by using 9 high-strength bolts and concrete adhesive. The test section B was a C30 reinforced concrete structure with thickness 0.3 m, which is cast on site. The test section C is a composite structure of C30 reinforced concrete with foam concrete backfill layer, with a thickness of the C30 reinforced concrete of 0.3 m, and a thickness of the foam concrete soft backfill layer of 0.45 m. In order to ensure that the foam concrete backfill layer and the supporting structure can be closely combined, the foam concrete backfill layer is constructed by adopting the cast-in-situ method. The C30 reinforced concrete layer, as well as the high-performance reinforced concrete layer, of the inner structure in the three test sections possess the same cross-sectional size, and the horizontal length, and vertical one, and the length of free surface of the inner structure are all 1.8 m. The schematic diagrams of the cross-sectional dimensions of each test section are shown in Figure 3.  
In order to effectively analyze the damage effect of the structure under the plane charge explosion loading, the test measurement mainly includes the structural mechanical parameters and the structural deformations, cracks, and failure forms.