## 3 Test Results and Analysis
### The Structural Dynamic Response Analysis
It can be seen that the vertical relative peak displacement of the high-performance reinforced concrete test section is the result of the combined action of the arch spring crack and the structural deformation, while that of the C30 reinforced concrete test section is generated by the hance crack, the arch spring plastic hinge and the structural deformation. Therefore, the vertical relative displacement of the C30 reinforced concrete test section is greater than that of the high-performance reinforced concrete one. As shown in Figure 13b, the transverse relative displacement of the high-performance reinforced concrete test section is 46.6 mm, which is 94.0% higher than that of the C30 reinforced concrete one. Under the same plane explosion loading, due to the tensile cracks in the vault of the high-performance reinforced concrete test section, it can be seen that the dynamic resistance strength of the vault exceeds the allowable value. At this time, the arch-wall junction bears a large outward horizontal thrust. However, the arch spring of the C30 reinforced concrete test section produces a compression shear damage and forms a plastic hinge, and the hance also produces a compression shear damage zone. The stiffness of the arch decreases, and the horizontal thrust transmitted from the arch to the arch-wall junction decreases. Therefore, the phenomenon increased the transverse relative displacement of the high-performance reinforced concrete test section appears. Comparing with the C30 concrete, various physical and mechanical properties of the high-performance concrete are improved, and the structural strength and resistance to deformation are increased. As the transverse relative displacement between two straight walls is large, the structure only produces intermittent cracks at the arch spring, which belongs to a lower damage grade compared with the C30 reinforced concrete structure. Figure 13: The time-history curves of the relative displacement of the structures: (**a**) the vertical relative displacement; (**b**) the transverse relative displacement. The vertical relative displacement of the composite structure is 19.9 mm, which is 37.0% less than that of the C30 reinforced concrete test section, and the transverse relative displacement is 3.27 mm, which is 93.0% less than that of the C30 reinforced concrete test section. It can be seen from Figure 13 that the lateral residual displacement of the test section of the composite structure has a minus relative displacement of 1.5 mm. Combining with the peak stress at the straight wall, the straight wall has not entered the plastic deformation stage, so it is impossible to produce a minus relative displacement. However, considering that the composite structure produces some microcracks at the arch spring, and the foam concrete layer between the surrounding rock reinforcement layer and the structural layer is also broken, the foam concrete is not strong enough to resist the minus relative displacement. Therefore, the micro cracks at the arch spring cause a minus displacement of 1.5 mm in the composite structure. When the impact load is transmitted to the composite structural test section, due to the existence of the foam concrete soft backfill layer, the foam concrete possesses the properties of wave absorption and energy dissipation, which results in reducing the load impulse to the structure. Furthermore, the measured static compressive strength of foam concrete is only 3.25 MPa, after damage to the surrounding rock, the foam concrete on the upper part of the arch structure will be crushed and compacted to cushion the impact load on the structure, and finally only some tiny cracks will be produced at the arch spring. Therefore, the foam concrete has an excellent energy dissipation effect, the vertical and horizontal relative displacements of the composite structure are small, and the composite structure has a better anti-explosion performance and less effect of injury.