## 2 Test Design and Program
### Test Program
Figure 3: The schematic diagrams of the cross-sectional dimensions of each test section: (**a**) cross-section of test section A; (**b**) cross-section of test section B; (**c**) cross section of test section C.  
Figure 2: The engineering layout of the test sections. Four pressure-measuring points are designed at the bottom of the explosion cavity to measure the load at the bottom of the explosion cavity. The carbon resistance pressure sensor packaged by the flat polymer is selected as the sensor, as shown in Figure 4. The working principle of the carbon resistance pressure sensor is based on the piezoresistive effect of the composite conductive material [33]. The sensor is a flat structure, and the packaging material is the emery epoxy polymer, which has a good match of mechanical properties with the concrete and rock medium. It is considered that the fireball in the explosion cavity after the explosion probably destroy the pressure sensor and the insulated conductor, and the stress wave generated by the adjacent in-line explosive in the explosion cavity will form the Mach reflection. In order to eliminate the above adverse factors, and facilitate data collection, the strategies of setting a groove in the rock medium at the bottom of the explosion cavity, and embedding the pressure sensors and the insulated conductor as well, are adopted to shield too many interference signals. The four pressure sensors are buried in the plane \(Z\) that is parallel to the bottom surface of the explosion cavity, and 5 cm from the bottom of the explosion cavity. Since the sensor is only 5 cm away from the bottom of the explosion cavity, it can be approximately considered as the pressure at the bottom of the explosion cavity. Figure 5a is the spatial position diagram of the pressure sensors, in which the upper top surface is the bottom surface of the explosion cavity. Figure 5b is the top view of Figure 5a. Figure 5b shows the placement position of the pressure sensor on plane Z. After the pressure sensors and the wires are laid out, the interface of the sensors and the insulated conductor is lined with epoxy resin for water-proof and moisture-proof sealing treatment. The insulated conductor is laid from the side of the explosion cavity through the trench, and then fixed with plain concrete after being firmly positioned. Figure 4: The carbon resistance pressure sensor. Figure 5: The transducer’s layout at the bottom of the explosion cavity (mm): (**a**) The spatial position diagram of the pressure sensors; (**b**) the top view of the plane Z. The central cross-section of three test sections was selected as the structural test surface, and five pressure measuring points (vault, hance, right arch spring, straight wall center, and floor center) are set on the inner layer of each structural test surface. Each measuring point is equipped with a carbon resistance pressure sensor, wherein the pressure sensors in the arch are perpendicular to the radius direction of the arch curvature, and the interface of the sensor and the insulated conductor are lined with epoxy resin for water-proof and moisture-proof sealing treatment. The DONGHUA DH5960 dynamic signal test analyzer is used for data acquisition and recording. The two points between the left and right straight walls, and that between the vault and the floor center, are arranged in each test section to measure the transverse and vertical relative displacement of the structure under plane charge explosion loading. The ranges of the selected displacement sensors used in this research are 200 mm.