On May 15, the Hankou Tunnel of the Xinjin Expressway was certified on site by Guinness World Records as the world's longest spiral highway tunnel. The tunnel was designed by Henan Provincial Communications Planning & Design Institute Co., Ltd. and constructed by CSCEC Road and Bridge Group.

According to reports, the Xinjin Expressway spiral tunnel group consists of 9 tunnels, winding two and a half circles along the Taihang Mountains, with a total length of 28 kilometers. Among them, the Hankou Tunnel, which was certified this time as the world's longest spiral highway tunnel, has a total length of 4,457 meters, lies between 784 and 893 meters above sea level, has an elevation difference of 109 meters between its entrance and exit, and a minimum curve radius of 700 meters. It features a long single tube, a large elevation difference, a small curve radius, and many spiral turns.

The Xinjin Expressway spiral tunnel group is located on the western edge of the North China Plain and in the Taihang Mountain range, with terrain high in the north and low in the south, and high in the west and low in the east. The route runs from south to north across three geomorphic units: plain and rolling hills, heavy hills and intermountain basins, and deep mountains. The elevation along the route ranges from 70 m to 1,730 m, with extreme topographic relief. To solve this problem, the project design team of Henan Provincial Communications Planning & Design Institute compared multiple options and ultimately chose a spiral tunnel group design, which is currently the world's only three-tier spiral tunnel group.

The Xinjin Expressway is an important expressway corridor in China's Taihang Mountains connecting Henan and Shanxi provinces, and an important north-south transport corridor in the Henan provincial expressway network plan. It starts in KuaiCunying Village, Dakuai Town, Fengquan District, Xinxiang City, Henan Province, and ends in Yingpan Village, Gujiao Township, Lingchuan County, Shanxi Province, with a total length of 69.75 kilometers. It was completed and opened to traffic on December 26, 2022. The construction of the Xinjin Expressway has effectively driven the development and revitalization of the old revolutionary base areas in the Taihang Mountains, and has greatly promoted mutual transportation, material circulation, tourism development, and industrial and agricultural production between Henan and Shanxi provinces.

　More news

Just how impressive is the Xinjin Expressway spiral tunnel group?

The design institute previously published a report article titled "Analysis of Key Technologies of the Xinjin Expressway Spiral Tunnel Group" on the "Transportation Strategy Research" WeChat public account. The full text of the report is as follows:

　　Analysis of Key Technologies of the Xinjin Expressway Spiral Tunnel Group

The Kuaicunying to Yingpan (provincial border) section expressway project of the Xinjin Expressway is an important north-south transport corridor in the Henan provincial expressway network plan, and was officially completed and opened to traffic on December 26, 2022. The project starts at the Kuaicunying interchange of the Hebao Expressway in Hongqi District, Xinxiang City, and connects with the Shanxi Linghou Expressway at Yingpan Village on the provincial border. It is an important corridor connecting Henan and Shanxi provinces. The entire line is built to a two-way four-lane expressway standard, with a total route length of 69.75 kilometers. The project area is located on the western edge of the North China Plain and in the Taihang Mountain range, with terrain high in the north and low in the south, and high in the west and low in the east. The route runs from south to north across three geomorphic units: plain and rolling hills, heavy hills and intermountain basins, and deep mountains. The elevation along the route ranges from 70 m to 1,730 m, with extreme topographic relief. To solve this problem, the project design team of Henan Provincial Communications Planning & Design Institute compared multiple options and ultimately chose a spiral tunnel group design, which is currently the world's only three-tier spiral tunnel group.

　I. Three-tier spiral alignment overcomes the problem of excessive terrain elevation difference

The final section of the project is located in the central-southern part of the main Taihang Mountain range, with overlapping peaks and steep cliffs. The elevation ranges from 800 m to 1,730 m, with extreme topographic relief. Among them, the straight-line distance from the Xinzhuang interchange to the terminal section is 7 km, with a design elevation difference of 780 m, and ordinary alignment methods cannot meet the requirements. After comparing multiple options, a spiral tunnel group was ultimately adopted for the alignment to reduce the longitudinal slope and overcome the elevation difference. The spiral tunnel group section has a route length of 28 km and a design speed of 80 km/h, with a total of 18.1 km/9 tunnels, using a three-tier spiral alignment along Jiaoding Mountain, with a minimum radius of 700 m, a maximum longitudinal slope of 3.95%, and a minimum longitudinal slope of 1.5%. It is currently the world's only three-tier spiral tunnel group.

　　II. Specialized design ensures the safety of structure crossings

The spiral alignment method of the project causes multiple vertical overlaps and crossings of the main line, including the crossing of the Nanma'an Tunnel and the Hankou Tunnel (vertical elevation difference of 343 meters), the crossing of the Liuyuan Tunnel and the Jiaoding Mountain Tunnel (vertical elevation difference of 156.8 meters), and the crossing of the Haoping Tunnel and the Shibanpo No. 2 Bridge (vertical elevation difference of 55.3 meters). The closest distance between the bridge pile foundation and the tunnel is about 9 meters. The Haoping Tunnel passes beneath the Jinniushi Service Area and Jinniushi Village (vertical elevation difference of 111.9 meters). During design, in response to the vertical overlapping and crossing characteristics of the structures, and while considering the disturbance conditions of cross-structure construction, specialized scheme designs such as optimizing bridge spans, pile foundation calculations, and controlled blasting were carried out to ensure the safety of crossing structures.

　　III. Dynamic design to traverse various unfavorable geological conditions

Due to multiple tectonic activities, the Taihang Mountain area where the project is located has formed a complex geological structure, with multiple lithologies such as mudstone, sandstone, argillaceous siltstone, and limestone distributed in layers or interbeds, with rock stratum dip angles of 5–6°, which are relatively small. There are various unfavorable geological conditions such as horizontal rock strata, karst, faults, and dangerous rock masses.

1 Horizontal rock strata

The rock strata in the project area are approximately horizontal. During tunnel excavation, unstable blocks at the top are prone to shear displacement along weak structural planes or interlayers, and to tensile cracking and falling. After blasting vibration and excavation disturbance, the tunnel crown is prone to block falling, overbreak, and collapse, forming a portal shape, which seriously changes the stress state of the structure and easily causes stress concentration in the rock mass, leading to safety accidents and posing a great threat to construction safety. The figure shows the collapse of an entire block at the crown after excavation in the Bailianshu Tunnel, with a length of 20 meters. During construction, measures such as advanced support, optimized controlled blasting parameters, weak scaling after excavation, emphasis on initial shotcrete, and adjustment of anchor bolt angles were adopted to solve related technical problems.

2 Karst

The strata in the project area are mainly limestone. During tunnel excavation, a large number of karst caves appeared, seriously affecting construction and operation safety. For example, water inrush from a karst cave in the Wangmangling Tunnel caused 300,000 cubic meters of water accumulation in the tunnel. During construction, economically effective measures such as "consolidation (strengthening support structures), spanning (bridge crossing below), prevention (backfilling permeable materials above to prevent rockfall), and drainage (ensuring system drainage capacity)" were adopted to solve the tunnel engineering problems.

3 Dangerous rock masses at tunnel portals

The terrain in the project area is steep, and the slope faces at the entrance of most tunnels are approximately 90°. After years of weathering, the rock masses have formed a large number of dangerous rock masses, seriously affecting tunnel construction and later operation safety. In response, during the design process, designers climbed among vines and vines and checked them one by one, and according to actual conditions adopted measures such as clearing dangerous rocks, active protection nets, passive protection nets, prestressed anchor cable reinforcement, and setting up inverted-cut bamboo portal sections, ensuring smooth tunnel entry and portal construction safety.

4 Sudden water inflow

The tunnel group passes through multiple fault fracture zones, with developed joints and fissures, broken rock, poor surrounding rock stability, and developed groundwater. Sudden water inflow occurred in many places during construction. According to on-site geological conditions, full-face deep-hole pre-grouting was used for water plugging and lining support was strengthened to ensure construction safety. At the same time, a drainage system was added behind the lining to facilitate the discharge of rock mass water. Through the combined measures of "plugging and drainage," tunnel construction and operation safety were ensured.

　　IV. Conversion of multiple coordinate zones safeguards project breakthrough

The starting point of the project is located on the North China Plain, with a ground elevation of 70 meters; the endpoint is in the deep Taihang Mountains, with a ground elevation of 1,730 meters. The natural elevation difference between the start and end points is 1,660 meters, and the design elevation difference is 1,210 meters, of which the design elevation difference of the spiral tunnel group section is 780 meters. Due to large measurement deformation and multiple projection planes in the mountainous section, 6 independent coordinate systems were designed during the survey and design process, with two or more common points set between adjacent coordinate sections and conversion parameters provided, ultimately achieving a projection length deformation value of ≤2.5 cm/km within the survey area and ≤1 cm/km for large structures, ensuring that the design coordinate accuracy meets requirements and safeguarding high-quality project construction.

　V. Overall consideration of ventilation and fire protection for the tunnel group to achieve energy saving and land saving

1 Ventilation

The tunnels in the tunnel group section are all long and extra-long tunnels, and all are one-way slopes with a gradient of 2.5%. The gradient is relatively large and the tunnel alignment is mostly curved, with a minimum radius of 700 m. The spacing between some tunnel portals is less than 50 m, and there is a problem of pollutant cross-flow between adjacent tunnels. In the design, the ventilation systems of some tunnels were considered as a whole, and multiple tunnels (the Bailianshu Tunnel and the Haoping Tunnel, the Jiaoding Mountain Tunnel and the Nanma'an Tunnel) were designed as one tunnel for the ventilation system, using a combination of jet fans and channel ventilation. In addition, considering the favorable factor of the large elevation difference between tunnel entrances and exits, the effective use of natural wind was studied, and ventilation equipment was configured according to slope differences, thereby achieving energy saving and consumption reduction.

2 Fire protection

Due to the steep terrain, most tunnel portals are nearly vertical slopes, and the spacing between some tunnel portals is small. Fire water tanks cannot be built due to terrain and landform restrictions, and water source replenishment is difficult. During the design process, relevant situations were checked one by one. After comparing multiple options, a design scheme using a stable high-pressure fire water supply system with booster equipment and multiple water supply sources was ultimately adopted, providing strong support for ensuring safe tunnel operation. At the same time, some tunnels share fire water tanks, solving the problems of fire water tank site selection and land use and saving 24 mu of land.

　　VI. Multiple measures to help ensure the operation safety of long steep downhill tunnel groups

As an important corridor between Henan and Shanxi provinces, the project has a large traffic volume. The spiral tunnel group alignment section is a 28 km long downhill section, with a bridge-tunnel ratio of 82.3%, a maximum longitudinal slope of 3.95%, a minimum longitudinal slope of 1.5%, and an average longitudinal slope of 2.78%. In addition, there is more rain and fog, and the road operation safety faces severe challenges. In the design, safety facilities such as active luminous signs and deceleration markings were added at small-radius locations, colored pavement and light-shading sheds were set at tunnel portals, and an active driving safety guidance system for fog areas was set up to provide safe guidance for vehicles. At the same time, facilities such as an escape lane (LK61+800) and a parking area (K45+700) were set up while overcoming complex terrain restrictions, providing self-rescue services for vehicles in emergencies. Considering that emergency rescue in tunnels may not arrive in time, two emergency rescue auxiliary passages were set up in the Liuyuan Tunnel (LK59+933) and the Nanma'an Tunnel (LK66+363). The combination of multiple measures ensures the operation safety of the project.

　VII. Conclusion

The completion and opening to traffic of the Kuaicunying to Yingpan (provincial border) section expressway of the Xinjin Expressway will further improve and optimize the layout of the province's expressway network, enhance the complementarity of the expressway network in northern Henan, open up the province's north-south transport corridor, promote the development of tourism in the southern Taihang Mountains, strengthen the connection between Shanxi and Henan provinces, and create better basic conditions for the rapid economic development of the areas along the route. At the same time, the design and application of the large-elevation-difference spiral tunnel group have also accumulated valuable experience and technical advantages for the design institute's subsequent mountain projects.