Damage Characteristics of the Shield Segment of the Subway Tunnel under Impact Loading

To investigate the damage characteristics of the shield segment of the subway tunnel under impact loading, the combined research method of the light gas gun experiment and the numerical simulation were adopted. The damage conditions of the tunnel shield segments subjected to impact loading were analyzed. By analyzing the stress states of shield segment elements, the failure mechanism of shield segment under impact loading was studied. Results show that with the impact position as the center, the surface of the shield segment specimen is mainly subjected to compression in the radial direction and tension in the circumferential direction, and the compressive strain is greater than the tensile strain at the same monitoring position. Under the impact of bullets with different velocities, the horizontal and vertical dimensions of the impact crater on the front of the segment are not much different. With the increase of bullet velocity, the size of the impact crater on the front of the shield tunnel segment increases and so does the depth of the impact crater. The equivalent diameter of the impact crater increases in a "three-stage pattern" with the increase of the impact velocity of the bullet. Along the bullet impact direction, the element stress state of the shield segment specimen changes from triaxial compression to triaxial tension. When impacted by the bullet, the concrete in the impact side of the tunnel shield segment will be crushed by compression and the concrete in the back of the tunnel shield segment will be damaged by tension. The research results can provide a certain theoretical basis for the impact resistance design of shield segment.