On July 5, the Songjiashan Tunnel, the longest tunnel on the entire Guangyuan-Mianyang expansion project of the G5 Beijing-Kunming Expressway (hereinafter referred to as the Guang-Mian Expansion Project) and one of its major difficult control works, was successfully holed through on both tubes. The project is invested in by Sichuan Expressway Company of Shudao Group as the lead investor, designed by Sichuan Provincial Highway Design Institute, and constructed by Sichuan Road & Bridge Transportation Construction Group. This marks a breakthrough in the construction of the Guang-Mian Expansion Project and lays a solid foundation for achieving full completion and opening to traffic.

The Songjiashan Tunnel is located in Liugou Town, Jiange County, Sichuan Province. Its left tube is 3,730 meters long and its right tube is 3,680 meters long, making it a twin-tube, two-way separated extra-long tunnel. The tunnel is a small-clearance tunnel with a high clearance and large span. It lies in an area of fault fracture zones, well-developed fissures, horizontally stratified rock masses and poor integrity. The overall geological conditions are unfavorable, making blasting extremely difficult.

Construction site

During construction, the participating units overcame adverse factors such as high temperatures and the flood season, continuously optimized construction plans, introduced advanced construction equipment and steadily advanced the construction schedule. In terms of safety management, they applied safety management systems such as the tunnel access control system, video surveillance system, personnel positioning system and blasting warning system to carry out all-round real-time monitoring and early warning of the tunnel, achieving zero accidents and zero casualties throughout the production process.

In terms of innovation leadership, the "three-spray, three-scrape" process was adopted to strictly control the flatness of the initial support and focus on improving the appearance quality of the tunnel's secondary lining. The advanced anchor bolt construction method was used to enhance the stability of the tunnel structure. At the same time, an annular light strip lighting system was introduced into the expressway project under construction, significantly enhancing visibility inside the tunnel and effectively preventing operational accidents. A longitudinal micro-mist system was used to effectively control dust concentration and significantly improve the tunnel construction environment, marking the first application of its kind in an expressway under construction in Sichuan. In terms of environmental management, environmental protection laws and regulations were strictly observed, construction areas were rationally planned, ecologically sensitive and fragile areas were avoided as much as possible, and the ecological environment of two provincial-level nature reserves, the Xihe Wetland and the ancient cypresses of Cuiyun Corridor, was protected to the greatest extent. In terms of complex geology, the eighteen-character principle of "advance pipe roof, strict grouting, short excavation, strong support, early closure and frequent measurement" was adhered to. Advanced technologies such as geophysical prospecting for advanced geological prediction and smooth weak blasting were used, and well-known experts were invited to the site for guidance on multiple occasions, ensuring the tunnel was holed through on schedule under the premise of construction safety.

Construction site

As of now, the Guang-Mian Expansion Project has completed a cumulative investment of 15.488 billion yuan, accounting for 53.06% of the estimated total investment of 29.191 billion yuan.

It is reported that the Guang-Mian Expansion Project is scheduled to be completed and opened to traffic in 2026. After completion, the expressway from Chengdu to Guangyuan and on to Shaanxi, a northbound route out of Sichuan, will be substantially expanded, existing traffic pressure will be greatly relieved, and safer, more comfortable, efficient and sustainable transport services will be further provided for the public, promoting the integrated social, cultural and tourism development of the areas along the project.

The Guang-Mian Expansion Project is an important part of the G5 Beijing-Kunming Expressway, the capital radial line in the longitudinal line 8 expressway network of the national "ten vertical and ten horizontal" comprehensive transport corridors. The project starts at Zhoujiahe in Guangyuan City (south of the Heishuitang interchange of the Lanzhou-Haikou National Expressway) and connects with the Hanzhong-Guangyuan expansion project of the G5 Beijing-Kunming Expressway under construction. It ends southeast of Weicheng Town in Mianyang City, with a total length of 123.984 kilometers and a bridge-tunnel ratio of 54.6%. It has 21 tunnels and 74 bridges, including 9 extra-large bridges, and 12 interchanges. It is designed as a two-way six-lane expressway with a design speed of 120 kilometers per hour.

The project is characterized by "one high, two many and three difficult", namely high design technical indicators; many regional cultural resources and many environmentally sensitive points; and difficult construction access road construction, difficult construction power supply and difficult spoil ground site selection. During project construction, all participating parties advanced the working mechanism of "efforts at the end, results at the terminal" in depth, comprehensively consolidated the "three basics" construction, opened up the "last meter" of safety production management, solidly carried out closed-loop management of "monitoring, measurement, early warning, supervision and verification" of the ecological environment during expressway construction, and took the initiative in ecological and environmental protection. With the implementation of the quality "red and black list" notification working mechanism as the starting point and special activities such as labor competitions and concrete quality and efficiency improvement as the carrier, they made good use of the "central laboratory" and "lead supervision office" and strove to eliminate common quality problems, improve project quality and build quality projects.

Since the start of construction, the Guang-Mian Expansion Project has successively built a smart beam fabrication yard, a smart engineering management center and an intelligent mixing plant. It has vigorously applied digital intelligent lining trolleys and actively introduced digital intelligent manufacturing platforms and equipment such as the tunnel intelligent safety management system and the intelligent CNC form traveler system, strengthening its efforts in digital and intelligent construction. At the same time, measures such as "optimized design, permanent-temporary combination, green construction, energy conservation and emission reduction" have been taken to promote the harmonious unity of highway construction and ecological environmental protection, accumulating experience in green development of expressway construction and improving quality and efficiency in ecological and environmental protection. After completion, the project will greatly relieve the traffic pressure on the G5 Beijing-Kunming Expressway, substantially enhance the service capacity of the comprehensive transport corridor northbound out of Sichuan, and further promote the social, economic and cultural development of the areas along the route.