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.

The dislocation and overbreak of tunnel inverted arch are serious when traditional blasting excavation technology is used. This is because traditional blasting technology does not adopt the smooth blasting method, and the angle of the perimeter holes is too large when drilled by manual rock drilling rigs. By therefore analyzing the traditional blasting excavation technique of invert, the cause of serious studiedthe smooth blasting technology for inverted arch is proposed based on the smooth blasting theory and a large quantity of engineering practice. Water decking charge structure is adopted in the perimeter holes, which can be adjusted according to the inverted arch shape. The spacing between the perimeter holes is 30~50 cm, and the thickness of the smooth blasting layer is greater than the perimeter hole spacing by 10~30 cm. Additionally, a drilling counterforce support is used to reduce the angle of the perimeter holes which can ensure each blast hole to be drilled to the design depth. After comparing the blasting effects of the proposed smooth blasting technology and traditional blasting technology for the inverted arch by field tests, the contour overbreak by the smooth blasting technology is far less than that of traditional blasting technology, and the cost of every 12 m tunnel excavation is reduced by 35.14%.