## 3 Experimental Design
### Measurement Point Arrangement  
A total of six pressure sensors, eight displacement sensors, and six acceleration sensors were installed for the test. (1) Pressure sensors  
Three pressure sensors were installed between the center section of each test section, from the arch crown to the arch foot, to measure the vertical explosion pressure at the arch crown, half arch, and arch foot. The normal direction of the pressure sensing surface of all pressure sensors was vertical upward, and they were placed at a distance of 5 cm from the hole wall. Wet loess was used for backfill consolidation. The specific locations are shown in Figure 4.  
(2) Displacement sensors  
Wall displacement can reflect the macroscopic damage of the cavern under explosion loads and indicate the explosion resistance ability of different reinforcement methods. The KD2009T displacement sensor from Donghua was used in this test. The displacement sensors were mainly installed at the center of the arch crown, half arch waist, arch foot, and sidewall, measuring the relative displacement between different wall positions and the bottom plate as shown in Figure 5. The maximum range of the displacement sensor at the arch crown and half arch waist positions is \(\pm\)100 mm, and the range of the sensor is \(\pm\)50 mm. The displacement sensors were installed on the center cross-section of the test section to study the deformation of the wall under explosive dynamic loads and the distribution of vertical damage in the cavern. The layout of the displacement sensors is shown in Figure 6.  
The displacement sensors were fixed on the support bracket welded before the test. The displacement bracket was made according to the dimensions after the two test sections were reinforced, with sufficient vertical and horizontal stiffness. The bracket was fixed to the ground through expansion bolts to avoid bracket oscillation or self-vibration caused by  
Figure 4: Pressure measurement point layout diagram: (**a**) conventional steel-bolt-reinforced test section and (**b**) RDEA-bolt-reinforced test section. structural vibration during the test, which would affect the test results. The bracket used in the test was welded with channel steel, and the structure is shown in Figure 5. Since this test used a group charge explosion at the top, which was a typical problem of local effects, the deformation was mainly concentrated on the arch crown and sidewalls, and the disturbance of the bottom plate is relatively small. The displacement sensor bracket was firmly fixed to the bottom plate, and the measured data are all the relative displacement between the different parts of the wall and the bottom plate. (3) Acceleration sensors  
IPE-type piezoelectric acceleration sensors produced by Donghua were used for this test, as shown in Figure 7. The IPE-type acceleration sensor has a built-in integrated circuit, which does not require an external signal amplifier. It directly outputs a recordable voltage signal with strong anti-interference ability. The acceleration sensor was installed on the inner wall of the structural layer. First, a deep hole with a diameter of 2 mm and a depth of about 20 mm was drilled vertically to the wall surface at the installation position. The nut was anchored in the installation hole by structural adhesive, and the acceleration sensor was finally fixed on the mounting nut and bonded with structural adhesive, as shown in Figure 8.  
Figure 5: Displacement sensor and bracket: (**a**) KD2009T displacement sensor and (**b**) displacement sensor bracket. Figure 6: Displacement measurement point layout diagram: (**a**) conventional steel-bolt-reinforced test section and (**b**) RDEA-bolt-reinforced test section. The wall acceleration sensors mainly measure the acceleration at the arch crown, side-wall center, and bottom plate of the central section of the test section below the detonation point.