On April 28, the Dachangshan No. 1 Tunnel on the Zhongshan-Kaiping Expressway, a control project and China's first expressway tunnel to undergo 'three-to-four' lane widening excavation, achieved a safe full-face breakthrough in a single tube. This is the first successful case in China of large-section widening excavation carried out on the basis of an already completed secondary lining in a single-tube three-lane expressway tunnel.

The project is undertaken by PowerChina Roadbridge Group. The breakthrough of the tunnel widening excavation fills a technical gap in the field of large-section tunnel widening construction in China, sets a new record for specialized construction technology in the domestic expressway infrastructure sector, and provides valuable experience for similar projects.

The right tube of the Dachangshan No. 1 Tunnel, which achieved the widening breakthrough, has a total length of 624 meters and a maximum burial depth of 140 meters, including 479 meters of Grade III surrounding rock, 73 meters of Grade IV surrounding rock, and 49 meters of Grade V surrounding rock. During the 'three-to-four' widening excavation, the already completed secondary lining had to be demolished before in-situ single-side widening excavation could proceed. The construction process is complex, highly difficult, and carries high safety risks, and there was no mature technology or successful implementation case in China.

To smoothly advance the tunnel widening construction, PowerChina Roadbridge Group specially organized top industry survey experts and tunnel experts to rigorously review the construction technical plan. On the basis of fully drawing on past construction experience and relevant technologies, the team made bold innovative attempts, repeatedly studied the key and difficult points, and determined a series of targeted technical methods.

To comprehensively ensure the safety and quality of the tunnel widening construction, the project construction team of PowerChina Roadbridge Group adopted advanced forecasting methods to strengthen geological prediction during construction, continued to improve relevant measures according to actual conditions, optimized construction techniques, and fully integrated advantageous resources in survey and design, engineering technology, construction management, and quality and safety assurance to advance the work in a coordinated manner.

During implementation, the project construction management team vigorously promoted BIM technology, rationalized the allocation of on-site resource inputs, ensured proper sequencing of processes, and had the entire construction team fulfill its responsibilities and leverage professional strengths to comprehensively guarantee the safe and orderly progress of the tunnel widening construction, striving to achieve optimal overall cost, input, and efficiency.

The successful implementation of the 'three-to-four' widening excavation of the Dachangshan Tunnel strongly confirms the technical feasibility of large-section tunnel widening and promotes new breakthroughs in related technologies within China's infrastructure industry.

The Zhongkai Expressway is an important 'horizontal' line in Zhongshan City's 'four vertical and five horizontal' expressway network and a key east-west expressway project connecting the Shenzhen-Zhongshan Link. The successful implementation of the tunnel widening has raised the construction standards and technological level of the Zhongkai Expressway, helped it handle larger traffic volumes, played an important role in promoting the high-quality and efficient construction of the Zhongkai Expressway project, and laid an important foundation for the future connection of the Shenzhen-Zhongshan Link between the east and west banks of the Pearl River Estuary.