On January 25, China's largest urban comprehensive transportation hub was completed and opened to traffic in Shapingba, Chongqing. How did this 8-story underground hub overcome the challenge of relocating 200 kilometers of dense, spider-web-like pipelines? Located in the core of a commercial district, with high-rise residential buildings only 6 meters away, how did the underground blasting construction minimize impact on the surroundings? Our reporter visited the designers and builders of the Shapingba comprehensive hub.
Creating “39 standard football fields” underground to solve traffic congestion and space shortage
To ensure a operating speed of 300 km/h, the Chengdu-Chongqing high-speed railway was “straightened by cutting curves” and a station was set up in Shapingba, Chongqing, shortening the route by 20 kilometers compared to bypassing Chongqing North Station, and reducing travel time between the two places from over 80 minutes to 58 minutes.
However, as Chongqing's busiest commercial district, would building a high-speed rail station in Shapingba add charm or add congestion? Moreover, the Chongqing Shapingba transportation hub is not just a high-speed rail station, but a major hub integrating high-speed rail, rail transit, urban railway, buses, taxis, social vehicles, and pedestrian traffic.
“To expand urban space and improve comprehensive land utilization, we must either ‘go up’ and build super high-rise buildings, or ‘go down’ and build underground projects. The Shapingba railway comprehensive hub project is the first application model in the country that combines both,” said Qu Jiakui, project commander of the Chongqing Shapingba Railway Comprehensive Hub Project of China Railway 17th Bureau Group. The Shapingba high-speed rail station will have a city complex developed above it, while “going down” to create the country's largest underground comprehensive transportation hub, solving the long-standing problems of traffic congestion and space shortage in the Shapingba area with new supply.
The hub extends 8 stories underground, with an area of 280,000 square meters, equivalent to creating 39 standard football fields underground. All transportation modes operate underground, and the longest distance for citizens or passengers to transfer between high-speed rail, subway, bus, taxi, and ride-hailing vehicles is no more than 200 meters, with walking transfer taking less than 3 minutes. Since all transportation modes are “hidden” underground, tens of thousands of nearby residents will no longer be disturbed by noise and vibration, further improving their quality of life and happiness index.
Ordinary buildings usually have only 3 underground floors, and in terms of fire protection and emergency rescue, they often only adopt simple sprinkler systems and fire compartments, without automatic fire extinguishing functions, making the entire fire protection system relatively simple. So how is fire protection handled for an 8-story underground transportation hub 47 meters deep?
Qu Jiakui introduced that 15 proportional mixing tanks with automatic control valves are installed inside the hub, and the mixed firefighting foam covers all fire points, enabling precise and rapid fire extinguishing. In addition, the hub is equipped with a new intelligent evacuation system that can intelligently choose the evacuation direction based on the fire location and the distance to safe areas on site, using arrow indicator lights to guide people to the nearest safe area, and taking fire elevators to quickly return to the ground, with the entire process taking no more than 2 minutes.
Relying on building information management technology, nearly 200 kilometers of pipelines were relocated without a single accident
During the peak construction period of the Shapingba hub, nearly 1,000 tons of steel bars were consumed daily, and the total length of scaffolding steel pipes used was 37,000 kilometers, equivalent to 1.7 times China's land border. Such a massive project was implemented in the commercial heart of a municipality directly under the central government, with the construction area only 6 meters away from the nearest residential building. Ensuring project quality while minimizing impact on the surroundings made the construction difficulty comparable to performing surgery on the heart.
Using information technology to peel away the “spider web”. The pipeline network in the hub area involves tens of thousands of pipelines, with a cumulative relocation and renovation length of about 200 kilometers, and the minimum spacing between pipelines is zero meters. Among them, just one 300-square-meter foundation pit at Tianchen Bridge required the relocation and modification of more than 300 cables. Due to their age, underground gas pipelines and rainwater/sewage pipes had deviated from the design drawings. How to avoid damaging the pipeline network during underground construction and causing water or power outages?
“We are like performing surgery on the heart, needing to cut, peel, and relocate tens of thousands of ‘blood vessels’ and ‘nerves’. Fortunately, with building information management technology (BIM), we relocated nearly 200 kilometers of pipelines without a single pipeline collision accident,” said Ge Qiang, chief engineer of the Chongqing Shapingba Railway Comprehensive Hub Project of China Railway 17th Bureau. Through BIM technology, design drawings can be turned into 3D renderings, accurately calculating the optimal construction plan, avoiding rework and accidents from the source, shortening the construction period by nearly 2 months, and improving overall efficiency by about 5%.
Controlling shock waves and accurately calculating vibration velocity. The Shapingba hub excavation volume reached 1.4 million cubic meters, entirely constructed by blasting. Since the start of construction in 2013, the project has conducted 5 to 6 blasts per day, using more than 500 tons of explosives in total. How to reduce the impact on surrounding buildings when conducting such intensive blasting underground in the center of a commercial district? The blasting used the most advanced digital detonators instead of traditional electronic detonators, controlling the blasting vibration velocity to 0.5 to 1 cm per second, far below the national standard of 2.5 cm per second, with no impact on nearby residents and buildings. Even Feng Shuyu, the only academician of the Chinese Academy of Engineering in the blasting field, praised: “This shallow controlled blasting in complex environments is precise and worth promoting.”