Recently, the Qizishan Tunnel of the Suzhou Changjiang Road South Extension Project successfully applied the stepping combined large-span lining trolley rapid cross-section change technology, achieving "one trolley, seven transformations" and efficiently advancing the tunnel's mined excavation construction. This also marks a major technical breakthrough for the project and provides an important reference for the tunnel construction field.

The Qizishan Tunnel adopts a stepping combined trolley and innovatively applies a stepping travel system and rapid cross-section change technology to meet the lining construction requirements of large-section and multi-section tunnels. The trolley has a span of about 30 meters, a height of about 12 meters, and a formwork length of 6 meters. By using the frames of two trolleys from the original double-arch tunnel in a paired configuration and replacing only some formwork, crossbeams, and columns, it achieves both improved construction efficiency and economic benefits.

Among these, the stepping travel system effectively avoids risks such as derailment, rolling, and overturning that are common with conventional rail-mounted wheel systems, and offers advantages such as smooth travel and stable parking. The rapid cross-section change technology can quickly achieve conversion between different cross-sections without dismantling the overall frame, by replacing only a small piece of top formwork and some columns and laterally contracting the two frames. This enables the trolley to improve construction efficiency and ensure construction quality while greatly reducing the operational risks caused by repeated disassembly and assembly.

Since the start of construction of the Qizishan Tunnel, the trolley has undergone a total of five stages of modification, ultimately achieving "one trolley, seven transformations": from a 15-meter-span double-arch tunnel trolley (97 tons) it first became a 28-meter-span large-span (I) trolley (153 tons), then a 26-meter-span large-span (II) trolley (150 tons); the standard-section trolley became a 23-meter-span large-span (III) trolley (135 tons), then a 19-meter-span large-span (IV) trolley (115 tons), and finally a 17-meter-span large-span (V) trolley (110 tons).

According to reports, with the assistance of the tunnel "Transformer," construction of the Qizishan Tunnel has progressed smoothly. At present, the mined tunnel in the north section is 85% complete, and the mined tunnel in the south section is 84% complete. Next, the Changjiang Road South Extension Project will firmly grasp the main line of safe production, continue technical research and innovative exploration, and advance project construction scientifically and efficiently.