In April, while northern China is still immersed in the lush greenery of spring, South China has already entered the heat of summer. Along the shores of Tieshan Port in the Beibu Gulf of Guangxi, expansive mangrove forests stretch across the coastline in dense layers of vibrant green. Egrets glide gracefully among the trees and perch on branches, while fish and shrimp swim freely in the shallow waters in search of food. Nearby, construction is in full swing on the Tieshan Port Cross-Sea Bridge, a key control project of the Hezhou-Zhanjiang High-Speed Railway being built by China Railway Major Bridge Engineering Group. Rows of bridge piers are rising from the fields and extending steadily toward the sea.

The Tieshan Port Cross-Sea Bridge spans 8.47 kilometers in total, including a 4.46-kilometer sea-crossing section. The alignment passes through both concentrated and scattered mangrove wetlands along the eastern and western shores of Tieshan Port, habitats that are home to rare protected marine species such as the Chinese white dolphin, horseshoe crab, and amphioxus. As a result, the project faces exceptionally stringent environmental protection requirements. Builders of Section 3 of the Guangxi segment of the Hezhou-Zhanjiang High-Speed Railway have implemented a series of targeted measures to protect these aquatic “national treasures” and preserve the region’s ecological beauty.

Design First: Protecting Nature at the Source

Viewed from above, the bridge piers of the sea-crossing section are still taking shape, while the construction trestle beside them already resembles a giant dragon winding gracefully through the mangrove forests.

“To minimize the impact on the mangroves, we deliberately avoided densely vegetated areas and routed the trestle through natural channels within the mangrove wetlands wherever possible,” said Zha Hao, Head of Safety and Environmental Protection for Section 3 of the Guangxi segment of the Hezhou-Zhanjiang High-Speed Railway at China Railway Major Bridge Engineering Group. To avoid the mangroves, the trestle was designed with at least eleven bends of varying sizes. As a result, its length doubled from just over two kilometers to four kilometers, significantly increasing construction costs.

Section 3 of the Guangxi segment is the only section of the entire railway that crosses habitats containing rare mangrove-associated species. The area between Piers 140 and 164 is particularly significant, representing the most concentrated mangrove zone along the entire Hezhou-Zhanjiang High-Speed Railway corridor. Mangroves are unique viviparous woody plant communities found in tropical and subtropical intertidal zones. They play a vital role in coastal protection, wave attenuation, seawater purification, and providing habitats for fish, shrimp, and birds. Often referred to as “coastal guardians” and the “green lungs of the ocean,” mangroves possess tremendous ecological value.

Mangrove protection was incorporated not only into the trestle design but also into the design of the main railway bridge. Most of the bridge’s 222 piers utilize simply supported beam structures with a spacing of 32 meters. However, in critical sections crossing mangrove habitats, continuous beam structures were adopted, increasing pier spacing to 128 meters.

“Using continuous beam structures allowed us to eliminate 33 bridge piers, which means creating 33 additional spaces where mangroves can continue to grow,” Zha explained.

From deliberately rerouting the trestle to intentionally reducing the number of bridge piers, the builders minimized environmental impacts at the design stage, truly achieving the goal of “building bridges without destroying greenery, and creating connections while protecting nature.”

Delivering on Commitments Through the Strictest Environmental Measures

For the builders of China Railway Major Bridge Engineering Group, who have constructed numerous large-span bridges across rivers, lakes, and seas, the technical challenges of the Tieshan Port Cross-Sea Bridge are manageable. Geological issues such as shallow overburden layers and underground karst formations have established engineering solutions. The real challenge lies in meeting the project’s exceptionally strict environmental requirements, making every construction activity a carefully controlled operation.

“Every mangrove tree is precious,” said Li Yadong, Technical Manager of the project’s Second Work Area. “The approved construction zone is extremely limited, leaving very little room for adjustment and significantly reducing our working space.” For example, cofferdams must be built at the smallest possible scale, making reinforcement installation and pile cap construction much more complex.

Yet this additional complexity is a necessary part of protecting the mangroves and fulfilling environmental commitments. Throughout construction, the project team has adhered to the strictest environmental standards while employing digital technologies to conduct inspections and monitoring of mangrove habitats, promptly identifying and eliminating environmental risks.

“Oil contamination and drilling slurry are the two greatest threats to mangrove ecosystems,” Li noted.

To eliminate pollution risks at the source, bridge pile foundations utilize a steel casing clear-water drilling method that requires no slurry for borehole formation, fundamentally preventing slurry contamination. In addition, pollution-control curtains are installed around construction sites to prevent the spread of drilling debris and sediment.

To address potential oil leakage from construction machinery, the project team selected high-performance marine equipment to reduce spill risks and deployed several electric rotary drilling rigs to further minimize oil emissions. Emergency materials, including oil collection trays and absorbent pads, are also maintained on site as preventive measures.

At the construction site, dump trucks move orderly along the trestle transporting drilling waste. Dedicated waste containers are installed at each pier location, and collected drilling debris is transported ashore for proper treatment. Surplus concrete generated on site is sent to batching plants for screening and recycling, enabling resource recovery and reuse of construction waste.

The project team also assigns personnel to regularly clean the trestle and surrounding areas. Construction vehicles must undergo tire washing before entering work zones, while mangrove leaves are routinely rinsed to help maintain a healthy growing environment.

Rare marine species such as Chinese white dolphins, horseshoe crabs, and amphioxus are frequently observed near the bridge site. The project team has enclosed construction zones with fine-mesh barriers to prevent species such as horseshoe crabs from entering work areas. During steel pipe pile installation, low-noise piling hammers are used and operations are scheduled during low tide to minimize disturbances to birds and marine life. Dedicated observers are also stationed on site to conduct real-time monitoring and early-warning activities for protected species.

Building Environmental Awareness: From Compliance to Stewardship

While robust environmental protection measures are essential, cultivating environmental awareness among personnel may be even more important.

On September 13, 2025, an unusual public lecture was held at the project headquarters of China Railway Major Bridge Engineering Group. The speaker was not a bridge engineering expert but Fan Hangqing, Director of the Guangxi Mangrove Research Center and the Guangxi Key Laboratory for Mangrove Conservation and Utilization. Through systematic learning, project managers deepened their understanding of mangrove conservation and gained practical knowledge on scientific environmental management.

Every newly recruited worker must undergo specialized training on mangrove protection. Only after successfully passing this crucial first step can they obtain authorization to work on site.

With environmental standards set so high, did the project encounter resistance?

“Yes,” Zha responded without hesitation. During the early stages of construction, disagreements frequently arose between managers and frontline workers. Some workers questioned the strict requirements and complained, saying, “We’ve never faced environmental rules this strict on other projects. Why are you making such a big deal out of it?”

But Zha understood that this was not excessive caution—it was a responsibility that demanded genuine commitment. From government regulators and project owners to contractors and supervision teams, all stakeholders have established a coordinated and rigorous framework for mangrove protection, leaving no room for compromise.

Relevant authorities in Beihai conduct daily site inspections and carry out unannounced spot checks without prior notice. Meanwhile, the project team consistently emphasizes environmental protection during meetings on a daily, weekly, and monthly basis. Under this continuous guidance and strict oversight, more and more workers have shifted from passive compliance to active stewardship.

Only by strengthening environmental awareness can workers truly take the mangroves into account during construction, Zha said. Although some mangroves had to be removed for unavoidable reasons and the project obtained the necessary permits, the team adhered to the principle of “avoid cutting whenever possible, minimize cutting where necessary, and prioritize transplantation whenever feasible.”

“Cutting trees would certainly be the easiest option, but we chose the most complicated approach because we wanted to protect every possible tree,” Zha said.

Standing on the shores of Tieshan Port and looking into the distance, clusters of mangroves remain firmly rooted in the intertidal zone, withstanding salty tides and strong winds while quietly protecting the blue waters and skies of the Beibu Gulf. Today, the builders of the Tieshan Port Cross-Sea Bridge are fulfilling their mission through dedication and protecting the environment through meticulous attention to detail. As they construct a vital transportation corridor spanning mountains and seas, they are also safeguarding the region’s vibrant ecological heritage and putting into practice the principle that “lucid waters and lush mountains are invaluable assets.”