Winter typhoons and summer monsoons regularly pummel workers and equipment. Strong tides churn in a sea crisscrossed by submerged pipelines and some of the busiest shipping channels in the world. Working platforms across the open ocean disappear into the horizon. These are just some of the extreme construction challenges that contractors must mitigate using prefabrication, technology and logistical prowess in their effort to construct the largest network of island-connecting bridges in the world.

The conditions are "the worst" that veteran offshore bridge builder Jiang Junbo has seen. "Our construction area is located in the open sea, without any shelter," says the vice president with Road & Bridge East China Engineering Co.

Located in the East China Sea southeast of Shanghai, the Zhoushan archipelago consists of thousands of small islands, about 100 of which are inhabited. Until recently, the only access was by sea or air. But in 2010, China completed a string of five cross-sea bridges to connect the mainland to tourism mecca Zhoushan Island, which also serves as an important fishery and industrial hotbed.

Multiple contractors, including Road & Bridge, are working concurrently under separate contracts to extend the expressway another 30 kilometers to reach Daishan Island, with a spur reaching Changbai Island. Meanwhile, the 8.8-km Yushan Bridge is being built to connect Yushan and Daishan islands. Together with the 2010 bridges, the roadway will stretch 86.68 km, the majority of it over water.  Future sections will complete a giant circular route through the Yangtze River Delta area, creating an economic and physical beltway linking Shanghai, Ningbo and Zhoushan. 

Multiple Worksites on Land and Sea

Under a $239-million contract, Guangdong Changda Highway Engineering Co. and CCCC Second Harbour Engineering Co. are constructing the Fuchimen Bridge, which connects the 2010 bridge to a new route that will travel north on Zhoushan Island. While the 1,493-meter-long connector bridge “may seem a little small” compared to the extreme spans found elsewhere in China, “it is still innovative in design,” says a project spokesperson. Inverted Y-diamond main towers support a steel and concrete composite bridge deck, used for the first time in the area.

When it wraps up this year, Fuchimen Bridge will connect to the $2.74-billion Ningbo-Zhoushan Port Main Channel Road, which began in 2016 and is scheduled for completion in 2022. The almost 28-km project consists of three bridges, two land tunnels and five interchanges and is divided into four contracts. The southwesternmost section that begins where Fuchimen Bridge leaves off is being built by Zhejiang Communications Construction Group Co. The route traverses a mountainous region of the island and includes two land-based tunnels and half of a cable-stayed bridge and its southernmost 152-m tower.

From there, China State Construction Bridge Corp. picks up with its section, employing dozens of ships and temporary platforms to construct the longest over-water segment of the main channel road. It includes 5.3 km of main roadway and a 4.5-km interchange and spur road that will connect to the small but important port island of Changbai. “The construction of this section is complex in form and structure, including a cable-stayed bridge and a maritime interchange with the highest degree of assembly,” says Cao Haiqing, project manager with China State.

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Moves Forward Despite Bitter Cold

To add even more complexity to what’s already an unusual high-wire act of engineering, Haiqing’s team will build the northern half of the cable-stayed bridge and tower and will be responsible for installing the final deck section to connect its half with the one built by Zhejiang. “It is very unusual [to have two contractors build either half], but we have a monitoring system between the contractors and the design is very precise,” Haiqing says.

The bridge foundations for the piers and towers feature some of the longest steel pipe piles used in the world, according to China State. The 1,384 obliquely inserted 2-m-dia steel pipe piles extend 109 m through 36 m of ocean and a thick layer of seabed muck before reaching bedrock.

China State contracted with consultant Tianjin Tianhe-Cloud Building Engineering Technology Co.  to provide modeling and analysis on the job. By combining seabed elevation models and borehole measurement data with the pile and foundation BIM model, Tianjin Tianhe optimized the insertion sequence for the multiple steel pipes needed for each foundation to prevent each subsequently installed pile from damaging or distorting the previous piles, says Jin Yangshuo, BIM senior engineer.

Hostile Environment

At 1,643 m, segment three (see map), being built by Road & Bridge East China Engineering Co. over the main navigable channel, will provide the port road’s visual centerpiece. Two main cable-stayed spans—each 550 m long—will allow 100,000-ton oil tankers to navigate below in either direction at full tide. Twin 187-m secondary spans and 78-m side spans form the approaches connecting to two other segments.

Crews are currently installing the seven piers required for the bridge foundation. Because of the time-consuming boat rides required to access the mid-ocean jobsites, the contractor constructed living quarters on temporary work platforms at each pier where crews live and work for two-week shifts. When conditions are unsafe, such as during the six typhoons that hit the area last year, “personnel and machinery are evacuated from the construction site to a designated safe place,” Junbo says. Because of the hostile environment, “the effective operation time of the project is very short. For example, only 13 days in January 2017 could be used for work,” he says. Only about 190 days per year offer weather clear enough for work. In addition, tides swing up to 3.67 m and wave heights can reach 4.5 m. Currents are strong, flowing up to 2.8 m per second.

To date, there have been zero incidents or injuries on the road’s over-water sections, according to Junbo and China State’s Haiqing.

Factory-Based Assembly

The hazardous conditions led contractors to collectively build extensive on-land prefabrication factories that produce much of the superstructure, with modules then shipped to the work platforms for final assembly. 

At the upper end of the size scale, workers prefabricated 42-m-long, 10-m-thick anticollision steel boxes to create the frames for mass-concrete platforms at the bridge pylons. Each box weighs 2,200 tons and has two rings. Fully preassembled inner rings are transported to the jobsite by boat and hoisted into place by a 2,600-ton floating crane (see cover). After the outer box ring is assembled on site, workers install a fully assembled rebar cage that fits around the tops of the foundation piles. To verify the feasibility of such a precise installation, BIM technicians at Tianjin Tianhe created a refined steel bar model and found 21 collision points. As a result of the BIM analysis, the team was able to correct 120 drawing faults and 624 collision points, which shaved off 50 days on pile construction work, according to Tianjin Tianhe’s Yangshuo. The effort landed the project as a finalist for infrastructure technology provider Bentley's Year in Infrastructure awards in 2018. 

Workers place 6,135 cu m of concrete into each box around the rebar cage to create a pier cap. Locations of temperature sensors embedded in the concrete are synced with the BIM model and alerts are sent to managers’ cellphones when temperatures rise too high. Computer controls can also automatically open condensing system valves to cool the concrete interior.

QR codes assist with tracking assembled components. Workers can also use their cellphones to scan QR codes via WeChat (China’s popular social media app) and watch animations of how to perform the day’s work. 

Grand Scale

The scale of work being performed simultaneously pushes the limits. On its segment, Road & Bridge crews drill concrete piles up to 3.5 m in diameter and 134.5 m deep for the three tower foundations. Assembled rebar cages are lowered into the holes and 1,200 cu m of concrete forms each pile. Once the cap and anticollision steel boxes are installed, work will begin on the elegantly curved 180-m-tall pylons, designed to mimic two hands held with palms together in honor of the area’s Buddhist history. Hydraulic climbing formwork creates the curve via a patented “integral adjustable curved surface template.” 

Where the main channel road terminates, Zhejiang Communications Construction Group Co. holds a separate contract for the Yushan Island project to construct an 8-km-long spur to Yushan Island. The contractor says this project is the first in the world to use segmental erection on steel-concrete hybrid girders and to use supersized 5-m-dia, 148-m-long steel-tube composite piles, instead of multiple-pile groupings, to help reduce construction time by 40% and cost by 30%. Crews spent three months building a modular 7.8-km continuous trestle system to ease transport of construction equipment, personnel and material in the harsh marine environment and increase the number of viable work days. Together, these steps reduced the construction schedule to just 27 months.

With the Ningbo-Zhoushan Port now the busiest in the world in terms of cargo tonnage, the fast-track effort to build the bridge network and, in the future, connect the roadway north to Shanghai forms a critical backbone for economic growth in the region.

Reported with the assistance of Construction Times, Shanghai