On January 20, with the success of the final blast in the left tunnel tube, the Hongtu Extra-Long Tunnel on the Dafenghua Expressway, owned by Guangdong Communications Group, achieved full connection after more than three years of construction, laying the foundation for the project to open to traffic in 2021.

The Hongtu Extra-Long Tunnel is located within Meizhou City and is designed as twin single-track tubes with a combined length of 12,686 meters and a maximum burial depth of about 740 meters. The tunnel combines adverse geological hazards such as complex faults and high-pressure mud and water inrushes, making it a bottleneck project for the entire line.

"Building a tunnel under a lake," water inflow "enough to fill three West Lakes"

The Hongtu Tunnel is a high-pressure, water-rich tunnel rarely encountered in Guangdong. Its enormous water inflow, high water pressure intensity and complex geological conditions are rare in the industry, and the builders vividly described the excavation process as "building a tunnel under a lake." Since construction began, the project builders have broken through 16 fault structures and multiple low-resistivity anomaly zones.

In April 2019, high-pressure water inrushes appeared at the tunnel's entrance and exit ends, with fissure water continuously spraying from the working face. Daily water inflow reached as high as 150,000 cubic meters, and the maximum water pressure reached 4.8 MPa. The water inflow lasted nearly a year, with a volume equivalent to three West Lakes. About 1.8 kilometers of the tunnel's exit end involved reverse-slope drainage construction, requiring pumping operations during construction, and "wading through water" became the norm for the workers.

"We pumped water for more than 500 days. Now that the pumping task is complete, we are very excited," said Zhang Shangen of the pumping team on the TJ3 contract section.

Cleverly passing through six water curtain caves, the tunnel dons a "protective shell"

Faced with the "roadblock" of high water pressure and abundant water inflow, the project adopted a "full-face advanced curtain grouting" solution to control the water, using seven cycles of curtain grouting for treatment. The grouting section totaled 280 meters in length, and the tunnel ultimately passed safely through six high-pressure, water-rich fault zones. Li Kai, Party branch secretary and director of the Dafenghua Management Center, explained, "Curtain grouting is like putting a waterproof protective shell around the tunnel, allowing groundwater to flow away through other fissures."

In addition, the project actively used advanced geological drilling, ground-penetrating radar and other detection methods to identify geological conditions, and promoted the use of multi-boom rock drilling jumbos and other mechanical equipment to reduce manpower through mechanization and ensure the safety of workers operating in water.

A 298-meter-deep tunnel shaft, equivalent to a 100-story building

Because the tunnel is long, ventilation conditions inside are relatively poor. While excavating the tunnel, the project also excavated a 298-meter-deep shaft for the tunnel, equivalent in height to a 100-story building.

The shaft is like a "straw" inserted vertically above the tunnel, strengthening the air circulation system inside, improving the hot and humid construction environment, removing harmful gases and allowing fresh air to be supplied more effectively. It will also be an important ventilation facility after the tunnel opens to traffic.

The Fenghua section of the Dafenghua Expressway is an east-west road network densification line in eastern Guangdong, with a total length of about 40 kilometers. After completion and opening to traffic, it will provide a more convenient channel for transport connectivity between Wuhua and Fengshun counties, shortening the journey from the original 1.5 hours to 40 minutes. It is of great significance for further improving the expressway network in northeastern Guangdong and promoting the integration of the Meizhou Soviet Area into the construction of the Guangdong-Hong Kong-Macao Greater Bay Area.