On September 15, reporters learned from the double-tube breakthrough ceremony of the Qiganshan Extra-Long Tunnel in Contract Section A3 of the Chengkou-Kaizhou Expressway that after four years of arduous excavation, the double tubes of the Qiganshan Extra-Long Tunnel, a key controlling project of the Chengkai Expressway, have been successfully holed through. This is also the second extra-long tunnel to be completed in the Chengkou section of the Chengkai Expressway.

It is understood that Qiganshan, locally also called Sanpai Mountain in Chengkou County, requires winding through more than 200 hairpin turns and takes about an hour to cross. Once the Qiganshan Tunnel opens to traffic, the crossing will take only 6 minutes.

The Qiganshan Extra-Long Tunnel is one of the key controlling projects along the entire line, with a total length of about 7.66 kilometers and a maximum burial depth of more than 1,400 meters. At the start of construction, the Qiganshan Tunnel was consistently regarded as the extra-long tunnel with the most complex geological conditions on the Chengkai route, more complex than the Chengkai Tunnel itself. Since construction began, unfavorable geological conditions such as karst, underground rivers, water and mud inrushes, high ground stress, gas, faults and fracture zones have been encountered 39 times, with the maximum water inflow once reaching as high as 19,000 m3/h, making it worthy of the name "museum of unfavorable tunnel geology."

Liu Mingkun, deputy project manager of the A3 bid section of the Chengkai Expressway under China Railway Construction Bridge Engineering Bureau Group, told reporters that both the entrance and exit of the Qiganshan Tunnel are located on steep cliffs, where the treacherous terrain makes passage impossible, so engineering materials for the tunnel portals could only be transported by hired horse caravans. Building the construction access roads was extremely difficult. Although the access road at the tunnel exit is only 1.8 kilometers long, it sits in mountainous terrain of 70° accumulation bodies, winding through the mountains like a series of stacked "Z" shapes. Due to terrain and geological influences, the access road construction plan was continuously optimized, and it took 10 months to complete the access road.

The Chongqing Chengkou-Kaizhou Expressway has a total length of about 128 kilometers, of which the Chengkou section is about 60 kilometers long, with a bridge-tunnel ratio as high as over 96%. The Chengkai Tunnel, Qiganshan Tunnel, Jiming Tunnel and Wujialiang Tunnel also form an ultra-long bridge-tunnel connected section of about 48 kilometers, a rarity in the world.

According to Shi Yao, owner's representative of the Chengkou Engineering Department of Chongqing Expressway Engineering Consulting Company, "Facing complex geological challenges, the project established a comprehensive advanced geological prediction system for the tunnel, promptly analyzed geological problems in the predictions, predicted unfavorable geological conditions ahead of the tunnel face in a timely manner, and dynamically adjusted the construction plan, thereby ensuring construction safety." At the same time, to ensure tunnel construction progress, the project promoted the concept of "mechanization replacing manpower and automation replacing workers," equipping the site with multi-boom rock drilling jumbos, concrete wet-spraying manipulators, geological drilling rigs, hydraulic invert trestles, secondary lining formwork trolleys, waterproof board installation trolleys, hydraulic trolleys for drainage ditches and cable trenches, and information-based monitoring systems, as well as high-precision fabrication equipment for tunnel arch frames, small conduits, anchor bolts and steel mesh, achieving mechanized tunnel construction and intelligent steel bar processing.

It is reported that after the Qiganshan Tunnel is holed through, it will connect to the Liaozhi Extra-Large Bridge. With a total length of about 330 meters, the bridge is China's first weather-resistant steel box arch bridge without coating and is also one of the key controlling projects of the Chongqing Chengkou-Kaizhou Expressway. The bridge adopts a single-arch-rib multiple rotation process combining vertical rotation, horizontal rotation and vertical rotation, a construction method that is the first of its kind in the country and sets a precedent and lays the foundation for subsequent multiple-rotation construction of single arch ribs in arch bridges.

According to the latest news from Chongqing Expressway Group, based on the current construction progress, the approximately 50-kilometer section from Zhaojia to Tanjia in Kaizhou of the Chengkai Expressway is expected to meet traffic-opening conditions this National Day. In 2022, the Chengkai Expressway will reach the Chengkou county seat, achieving Chongqing's goal of "expressways in every county" nearly a year ahead of schedule. In 2026, it is expected to connect with Shaanxi, opening a fast interprovincial corridor between Shaanxi and Chongqing.

After the entire Chengkai Expressway opens to traffic, it will provide solid transportation support for poverty alleviation and revitalization in the contiguous poverty-stricken areas of the Qinba Mountains, and is of great significance for achieving the full connection of the G69 Yinchuan-Baise Expressway and improving the national road network.