Construction workers celebrate the safe and smooth holing-through of the tunnel.

On the morning of August 3, with a resounding blast, the Deqing Tunnel—the highest-risk tunnel in terms of rock-stratum conditions on the Guinan High-Speed Railway—was successfully holed through two months ahead of schedule. This also marks the successful resolution of the biggest challenge in the entire line's tunnel engineering, pressing the "fast-forward button" for the completion of the remaining tunnels.

Located in Hechi City, Guangxi, the 6,610-meter Deqing Tunnel is a key controlling project of the entire Guinan High-Speed Railway and the highest-risk tunnel on the line. The tunnel passes through a typical karst landscape area, with nearly half of its bore surrounded by Grade V surrounding rock—the least stable rock stratum. Adverse geological features such as karst caves, karst grooves, and dissolution-fractured zones are found everywhere. On average, a karst cave is encountered every 50 meters of excavation, and the entire tunnel contains more than 200 karst caves and cavities, making construction highly difficult. The tunnel also has nearly 2,000 meters of roadbed in deep, thick clay layers with very poor bearing capacity; if such swamp-like soil layers are not handled properly, they can easily cause subsidence and depression.

To ensure smooth construction, the Yungui Railway Guangxi Company and China Railway No. 2 Engineering Group adopted the most advanced "smooth blasting method" used in domestic high-speed railway tunnel construction. Compared with traditional construction techniques, smooth blasting produces fewer flying rocks and can form a flat blasting surface. At the same time, 3D scanners can be used to collect rock-stratum data and analyze it in real time, calculating and optimizing the quality, spacing, charge distribution, and charge quantity data of the tunnel blast holes, effectively ensuring the stability of the rock strata around the tunnel.

To improve the bearing capacity of the clay layer, the construction unit adopted a pile-raft structure construction technique for the tunnel foundation, driving more than 1,000 piles in the clay-layer sections and then laying sturdy raft slabs. These reinforced-concrete piles and raft slabs feature high bearing capacity and small settlement, ensuring to the greatest extent the safe and smooth operation of trains in the future.

The Guinan High-Speed Railway spans northwestern Guangxi and southeastern Guizhou. It is the first high-speed railway in Guangxi designed for a speed of 350 kilometers per hour, and an important component of the new north-south land corridor connecting the Belt and Road Initiative. It is of great significance for Guangxi in vigorously advancing the construction of the New Western Land-Sea Corridor and accelerating the establishment of a new open-development pattern of "southward outreach, northward linkage, eastward integration, and westward cooperation." The entire line is expected to open to traffic by the end of 2023, when travel time from Nanning to Guiyang will be shortened to just over two hours.

The Deqing Tunnel.

As of now, the subgrade earthwork, bridge engineering, and tunnel engineering of the Guangxi section of the Guinan High-Speed Railway have completed 85.6%, 81%, and 78% of the designed total, respectively. Of the 45 newly built tunnels, 31 have been successfully holed through. In the second half of this year, bidding work is planned to be launched for later-stage high-speed railway construction projects such as station buildings, communications, signaling, and power supply.