On January 13, 2021, the first and most difficult mined tunnel section of the Nanning Airport Tunnel project undertaken by the Third Company of China Railway First Group was holed through, providing a guarantee for the opening of the entire line and greatly boosting the morale of all participating employees.

Liang Qilian and Tang Bo, deputy general managers of Guangxi Nanning Airport Comprehensive Transportation Hub Construction Company; Fan Xuebo, director of the Transportation Business Department of CIECC Engineering Management Consulting Co., Ltd.; Duo Ranwei, deputy general manager of the Third Company of China Railway First Group; and all project staff and participating construction teams jointly witnessed this victorious moment.

The newly built Nanning-Chongzuo Railway passes under Nanning Wuxu Airport and is part of the Wuxu Airport Comprehensive Transportation Transfer Center. The Wuxu Airport Tunnel has a total length of 7,465 meters and consists of three parts: the Nanning-end interval tunnel, the Wuxu Airport underground station, and the Chongzuo-end interval tunnel.

The Third Company undertook the construction of the 3,320-meter-long Nanning-end interval tunnel, including a 1,294-meter mined tunnel section. The contract period runs from April 1, 2020, to April 30, 2021. Based on the monthly advance rate for tunnels in Grade V surrounding rock, it would be difficult to meet the schedule requirements. Through on-site surveys and active communication with the owner and the design unit, at the start of the project, a cut-and-cover inclined adit was added through a change and optimization to open up additional working faces. After the change, the working faces were the tunnel entrance face, the newly added inclined adit face toward the smaller mileage, the newly added inclined adit face toward the larger mileage, and the tunnel exit face.

The tunnel section holed through this time runs from the entrance to the smaller-mileage side of the newly added inclined adit, with a total length of 370 meters. The maximum buried depth of this section is 10.5 meters, and the minimum is 3.4 meters. The tunnel portal is located in a foundation pit 21 meters from the original ground surface. Of this section, 100 meters passes beneath National Highway G322 with a buried depth of only 10.5 meters; 50 meters passes beneath Mingyang Industrial Park Avenue with a buried depth of only 3.4 meters; 60 meters passes beneath muddy miscellaneous fill landscaping with a buried depth of only 3.4-4.5 meters; and 20 meters passes beneath the piers of the existing Airport Second Expressway ramp bridge with a buried depth of only 4.8 meters.

Facing numerous risks, all project personnel tackled the difficulties head-on. Adhering to the principle of safety first, they pooled their wisdom, made reasonable plans, organized carefully, and implemented strictly. In response to the special topography, ground conditions, and geology of this section, they conducted detailed research and deployment. For the section beneath National Highway G322, they adjusted and strengthened the advanced support measures inside the tunnel. For the section beneath Mingyang Industrial Park Avenue, they adopted a cover slab beam scheme combining permanent and temporary works and carried out reinforcement in advance. For the section beneath muddy miscellaneous fill, they used surface sleeve valve grouting to consolidate it in advance. Through these measures, the construction risks of this tunnel section were greatly reduced, construction safety was ensured, and a strong guarantee was provided for safe and smooth holing through.