Recently, the double-arch section of the Qizishan Tunnel in the Suzhou Changjiang Road South Extension Project successfully completed all excavation and lining construction tasks, laying a solid foundation for the next phase of the project.

　　The left-line arch section of the Qizishan Tunnel is 185 meters long, and the right-line arch section is 395 meters long. The double-arch section refers to a structure composed of two adjacent arched tunnels, featuring high load-bearing capacity and good mechanical performance. The maximum cross-section span of the double-arch section is 29.33 meters, the minimum clear distance between the left and right lines is only 7.1 meters, and the cover depth is only 4.5 meters, making it an ultra-shallow-buried tunnel. With an excavation area of 264 square meters, it is an ultra-large cross-section tunnel, presenting extremely high construction difficulty and technical requirements.

　　To effectively solve the construction technical challenges and ensure smooth construction, the project carried out dedicated technical research and developed the construction method of "rapidly transitioning from a long-distance double-tube double-arch tunnel to a large-span single-tube tunnel," which was successfully applied to the construction of the north-side double-line arch tunnel. This cleverly avoided the construction organization challenge of the long duration required for multi-drift construction, providing new ideas and methods for the combined construction of arch tunnels and large-span tunnels.

　　The successful completion of all construction tasks for the double-arch tunnel not only marks the project's increasingly mature mastery of double-arch tunnel construction technology, but also sets an example for similar projects in the future.