On January 23, China's largest-diameter shield tunnel under construction for combined road and rail use, known as the 'First Tunnel Under the Yellow River,' was fully connected. Beside the Luokou floating bridge ferry crossing in Tianqiao District, as the massive cutterhead of the 'Yellow River' shield machine broke through the soil, the west-line tunnel of the Jinan Yellow River Tunnel Project, invested in and built by Jinan Urban Construction Group and constructed by China Railway 14th Bureau Group, was successfully connected. With this, China's largest-diameter shield tunnel under construction for combined road and rail use, known as the 'First Tunnel Under the Yellow River,' was fully connected. According to plan, the tunnel will be completed and opened to traffic in October this year. By then, driving across the Yellow River will take as little as 4 minutes, and riding the metro will take 2.5 minutes, saving nearly an hour compared with detouring via the Jinan Yellow River Bridge.

'Yellow River' and 'Taishan' Super-Large Shields Cross the Above-Ground 'Suspended River' for the First Time

The Jinan Yellow River Tunnel Project is located on Jinan's central urban axis, connecting Jiluo Road in the main urban area to the south and the New and Old Kinetic Energy Conversion Pilot Zone to the north. The project route is 4,760 meters long, with a tunnel length of 3,890 meters, including a 2,519-meter shield section. It is designed as a twin-tube, double-level structure combining municipal roads and rail transit: the upper level is a six-lane dual-carriageway road, and the lower level is rail transit. The tunnel segment outer diameter is 15.2 meters, making it the largest-diameter tunnel in the Yellow River basin and the largest-diameter shield tunnel under construction in China for combined road and rail use.

It is understood that the project adopts the EPC (engineering, procurement, and construction general contracting) model. The client is Jinan Urban Construction Group, the supervision unit is Shanghai Municipal Engineering Management Consulting Co., and China Railway 14th Bureau Group leads an EPC general contracting consortium formed jointly with China Railway Siyuan Survey and Design Group and Yellow River Design Company.

After the Yellow River flows into Henan, it begins to form an above-ground 'suspended river.' In the Luokou section of Jinan, the riverbed is 5 meters higher than the ground in the south bank urban area, and the maximum flood level is 11.62 meters above the riverbed, making it a rare above-ground 'suspended river' with enormous water volume. Starting in September 2019, the 'Yellow River' and 'Taishan' super-large-diameter slurry balance shield machines, jointly developed by Jinan Urban Construction Group and China Railway 14th Bureau Group, successively began excavation, marking the first great crossing of an above-ground 'suspended river' in human history.

The 'Yellow River' and 'Taishan' shield machines are 166 meters long and weigh 4,000 tons in total. The cutterhead excavation diameter is 15.76 meters, equivalent to the height of a five-story building. The lowest point of the tunnel is 54 meters below the riverbed, and the maximum water and soil pressure is 6.5 bar (equivalent to two adult men's weight bearing on an area the size of a human palm). Crossing the above-ground 'suspended river' over a long distance and with a large cross-section involves great construction difficulty and high risk, and will surely become another feat in humanity's development and utilization of the Yellow River.

Dual Floodgates Designed to Solve Challenges Such as Compact Cross-Section Layout

How can a tunnel be built to pass from a bustling city through a 'suspended river'?

The design team from China Railway Siyuan Survey and Design Group, led by Xiao Mingqing, a national survey and design master, chief expert of China Railway Construction Corporation, and deputy chief engineer of China Railway Siyuan Survey and Design Group, proposed a dual floodgate solution to achieve all-round effective sealing and protect urban safety.

To expand urban space, the Jinan Yellow River Tunnel is designed as a combined municipal road and rail transit project to maximize tunnel space utilization.

So how was the challenge of combined road and rail construction and compact cross-section layout solved? It is understood that the 'First Tunnel Under the Yellow River' is designed as a twin-tube, double-level shield tunnel for combined road and rail use. The upper level has a six-lane dual-carriageway road, while the lower level contains rail transit as well as smoke exhaust passages, utility galleries, and escape passages, maximizing the utilization of a single crossing of the Yellow River and greatly reducing environmental impact.

He Yingdao, a senior engineer in the tunnel specialty at China Railway Siyuan Survey and Design Group, said that to meet the clearance requirements for road and metro traffic, the group developed a height-adjustable precast box culvert, which can reduce the tunnel inner diameter by 20 centimeters compared with conventional schemes. This not only directly saves project cost but also maximizes space utilization and conserves land resources.

With the tunnel so deep underwater and with combined road and rail construction, how is rescue guaranteed in emergencies? 'The Jinan Yellow River Tunnel Project is equipped with complete disaster prevention and rescue facilities such as fire hydrants, water spray systems, fire extinguishers, broadcasting, emergency telephones, video surveillance, and equipment monitoring. Through a central computer, these form an organic system. In the event of an emergency, evacuation of the upper-level road can be completed in 6 minutes, and evacuation of the lower-level metro section can be completed in 30 minutes,' He Yingdao said.

Through the arduous efforts of the design, construction, and supervision units and thousands of employees, the east-line tunnel was the first to be connected on October 30, 2020, and the west-line tunnel was connected afterward. Based on effective excavation time statistics, average steady excavation reached 10.8 meters per day, setting the latest record for construction of similar tunnels.

Welded Steel Plate Thickening 'Patches' Overcome Multiple 'Attacks' in Composite Strata

Shield tunnel construction beneath rivers, lakes, and seas is one of the construction industries with the highest thresholds worldwide due to greater construction risks and high technical content.

After 15 years of exploration and refinement, China Railway 14th Bureau Group has become a 'front-runner' in this field. In particular, the bureau's large-diameter shield team has crossed the Yangtze River 13 times and holds more than 40% of the market share in China's super-large-diameter shield tunnels of 14 meters and above. In the excavation of the Jinan Yellow River Tunnel, five technical challenges—large cross-section, long distance, shallow cover, deep foundation pit, and high water pressure—were overcome one by one by the large-diameter shield builders of China Railway 14th Bureau Group.

'The biggest challenge was the irregular distribution, and even intersecting occurrence, of calcareous concretions and silty clay, which caused cutter teeth to break, pump blockage, sluggish discharge, and large volumes of waste slurry during shield excavation,' said Du Changyan, project chief engineer of China Railway 14th Bureau Group. The rock strength encountered during excavation generally reached 45 MPa and up to 90 MPa, more than twice the reinforced concrete strength of high-speed rail bridge piers. In the most difficult instance, only 2 meters were excavated in 26 hours, and 58 hard rocks were removed.

Large calcareous concretions blocked the grid, causing difficulties in slurry discharge in the slurry circulation system and, in severe cases, leading to shutdowns and worn-through pipes. Under the leadership of the Li Haizhen Innovation Studio and with guidance from an academician and expert team, engineering and technical personnel designed and installed a stone collection box on the shield machine, switched to new molded pipes, reversed the use of inlet and outlet slurry pipes, and welded steel plate thickening 'patches' in advance at pipe locations prone to wear to cope with impacts from hard rock.

According to Dong Bing, person in charge of the east-line tunnel shield, the east-line tunnel encountered a 1-kilometer 'dense zone' of calcareous concretions. With craftsman-like wisdom, they overcame one difficulty after another, and these results were then applied to the west-line tunnel, avoiding a repeat of the 'detours' in the other tunnel's construction and greatly improving construction efficiency.

[Related News] From the 'Daming Lake Era' to the 'Yellow River Era': A New Chapter Opens for Jinan's Northward Development Across the Yellow River

A great river runs through the city. Nanjing, Wuhan, Hangzhou, Guangzhou, Changsha, Tianjin, Lanzhou... the tide of development around and along rivers rises one after another, surging forward.

The Yellow River, the mother river of the Chinese nation, winds its way to Jinan. From Dong'e in Pingyin upstream to Renfeng in Jiyang downstream, it flows from west to east through 9 districts (counties) over more than 180 kilometers, accounting for nearly one-third of the total length of the Yellow River channel in Shandong, magnificent and spectacular.

Once, because it frequently burst and flooded, the Yellow River became a bottleneck constraining Jinan's development. Today, the Yellow River's major floods have been brought under control, with no flood for 38 years and no flow cutoff for 20 years. The Yellow River water is becoming 'clearer' and provides a steady supply of urban water for Jinan.

Jinan is deeply implementing the national strategy for ecological protection and high-quality development of the Yellow River basin, moving from competition between people and water to harmony between people and water, and from traditional river management to modern river management. Turning the Yellow River into an in-city river is a major strategic move for the development of the spring city, and a new chapter in Jinan's northward development across the Yellow River has thus begun.

The Jinan Yellow River Tunnel Project is one of Shandong Province's landmark projects for new and old kinetic energy conversion. After the tunnel is completed, Jinan's central urban axis will extend north across the Yellow River, reaching National Highway 309 and Jinan's northern new city. Along the route are important infrastructure and commercial centers closely related to Jinan residents, such as Jinan Coach Station, the largest passenger station in North China, Jinan Railway Station, Jinan Zoo, and Luokou Clothing City. Through the Yellow River Tunnel, it takes 4 minutes to cross the river by car and 15 minutes to reach the city center.

Breaking through the natural barrier and accelerating the northward crossing, the pilot zone is changing with each passing day through industrial transfer, supporting facilities, scenic area development, and population gathering. A new center of Jinan is emerging, and Jinan is accelerating its shift from the 'Daming Lake Era' to the 'Yellow River Era.'