The eastern and western main towers of the Shiziyang Grand Bridge were topped out on Thursday morning, signaling notable progress in the control project of the under-construction Shiziyang Link in the Guangdong-Hong Kong-Macao Greater Bay Area.

The bridge is part of the main construction of the 35-kilometer-long Shiziyang Link, which also comprises land-based approach projects.

The link crosses the crucial throat of the A-shaped Pearl River estuary, connecting Nansha district in Guangzhou, the capital of Guangdong province, with Shatian and Humen townships in Dongguan.

Each main tower stands 342 meters tall, equivalent to a 110-story building, according to the Guangdong Transportation Group.

Considering factors such as dense waterways and the scarcity of cross-river passage line resources, the link was designed to include the suspension bridge with a main span of 2,180 meters crossing the river in one leap, and a double-deck structure with 16 lanes.

Drilling for the first main pier pile foundation of the bridge began in April 2023.

Once completed, the project will set five world records for a double-deck suspension bridge in terms of main span length, number of lanes, main tower height, anchor diameter and main cable diameter, according to the group.

"As construction progresses, the project has achieved breakthroughs in structural systems, manufacturing processes, new materials and large-scale equipment," said Li Jian, general manager of the Shiziyang Link project.

The project has gradually developed a comprehensive technological system and standards for double-deck suspension bridges with spans over 2,000 meters, significantly helping advance China's technology for ultra-longspan suspension bridges, according to Li.

To accommodate the pressure of over 200,000 metric tons on the main towers, as well as the bridge's extra-wide deck and large span, the towers adopt a new steel plate-concrete composite tower structure. Compared to a concrete tower structure, the design reduces the wall thickness of the tower columns by 50 percent, decreases concrete usage in the main towers by 43 percent, with carbon dioxide emissions lowered by over 53,000 tons.

"The new design significantly reduces the self-weight of the tower and greatly enhances structural stability," said Zhang Taike, chief engineer of the Shiziyang Link project, from the Guangdong Transportation Group.

Building the bridge is not only a technical challenge but also an innovative practice, according to Kuang Yicheng, chief engineer of the T9 section of the Shiziyang Link project, from Poly Changda Engineering Co.

"To accommodate the tower structure, we have used C80 concrete, which has a strength equivalent to withstanding 8,000 tons of pressure per square meter, on a large scale in the tower field for the first time," said Kuang.

Compared to the previous practices, there were higher requirements for performance stability, and each single pour exceeds 300 cubic meters, leading to a significant hydration heat effect, which makes crack control difficult, according to Kuang.

"The pouring process is just like baking a cake, where external cooling causes contraction and internal heat cannot dissipate — this pushing and pulling can easily lead to temperature difference, affecting the project's durability," said Kuang.

After more than one year's research, constructors developed an air-cooled aggregate system and an intelligent pouring platform that integrates automatic temperature measurement, flow adjustment and precise vibration positioning.

"The system helps ensure accurate temperature control and pouring quality throughout the entire process," said Kuang.

Following the latest progress, the bridge project will move into the superstructure construction phase, according to the Guangdong Transportation Group.

Preparations for cable saddle installation and catwalk construction are also underway, with plans to have the pilot cable cross the river in the second half of this year.

qiuquanlin@chinadaily.com.cn