At 9:18 on July 8, the Xuantian Lake Tunnel on the Chengdu-Chongqing Middle Line, built by China Railway No. 5 Engineering Group, was successfully holed through. This is the first tunnel to be completed in Tongliang within the Chongqing section of the Chengdu-Chongqing Middle Line, marking the project's entry into an accelerated construction phase.

The Xuantian Lake Tunnel is located in the Xuantian Lake Scenic Area in Tongliang District, Chongqing. It lies in the denuded parallel ridge-and-valley region of eastern Sichuan, a broad, gently rolling hilly landscape with alternating hills and troughs and undulating terrain, where environmental protection requirements are stringent and construction is difficult. According to reports, the tunnel is a single-tube, double-track tunnel designed for a speed of 350 km/h, with a total length of 527 meters. It connects the Xuantian Lake double-track bridge and the Huanhu Road double-track bridge, occupying a critically important position in the project.

To ensure the smooth holing-through of the Xuantian Lake Tunnel, the participating construction units strengthened protection of the reservoir dam and the ecological environment of the Xuantian Lake Scenic Area, adopting controlled blasting for excavation, which protected nearby structures while also ensuring the construction schedule. During construction, the builders found three karst cavities inside the tunnel, which posed great challenges to the work. By continuously strengthening geological surveys and initial support, and adopting the approach of replacing and backfilling the cavities, they ensured orderly progress of construction.