Construction site of Phase I of the Yefeng Road project in Haitang District, Sanya. Photo courtesy of China Railway No. 4 Engineering Group

"The crane is too close to the foundation pit. Please adjust it immediately!"

"Received, executing immediately!"

At 7:30 on November 26, Zhang Lei, deputy chief engineer of the Phase I Yefeng Road project in Haitang District, Sanya, had just "clocked in" and walked straight into the project's monitoring room.

Seven monitoring screens displayed real-time activity across the construction site. With a walkie-talkie held to his mouth, Zhang Lei focused intently on each screen, and whenever he spotted non-standard construction behavior, he immediately notified the relevant personnel to correct it.

As a provincial key project, the Haitang District Yefeng Road project, with a total length of about 5.3 kilometers, adopts a design combining an underground vehicular system with an at-grade road (two-way, four lanes). Built by China Railway No. 4 Engineering Group, it will be constructed in three phases and is Hainan's first extra-long underground municipal road.

"On the first day of construction, we installed monitoring equipment on site to ensure 24-hour real-time monitoring of construction progress," Zhang Lei said. Initially there were only two cameras, now increased to seven, "and more will be added as needed in the future."

With monitoring assistance, efficiency has also improved. In the past, project management personnel had to conduct on-site inspections one by one; now everything is clear at a glance on the screens, and it takes only a few minutes from issuing an instruction to its execution.

"Old Gao, you're about to 'take off' again!" Stepping out of the monitoring room, Zhang Lei saw Gao Junjie, director of the comprehensive office of the China Railway No. 4 Engineering Group project, controlling a drone and preparing for takeoff.

The Phase I Yefeng Road project plans to build about 1.56 kilometers of at-grade road and about 1.96 kilometers of underground road. About 230 workers and multiple pieces of machinery and equipment are operating in an orderly manner at the construction site.

To achieve efficient and orderly construction coordination, it is necessary to grasp the "full picture" of above-ground and underground construction, and ensure effective operation through overall allocation. "Monitoring can cover ground-level scenes, while the underground construction portion requires drones to play their role," Zhang Lei said.

As the drone rose to a height of several dozen meters, the construction conditions in every underground corner were clearly visible on the operating screen. Gao Junjie skillfully controlled the drone and conducted a comprehensive high-altitude "scan" of the project construction site.

He Lü, head of the Phase I Yefeng Road project at Haitang Bay Development Company under Sanya Haitang Bay Investment Holding Company, said that drones are not only used for aerial inspections but can also record conditions at the construction site and display them at weekly project meetings, allowing everyone to intuitively understand project progress and existing problems. "Video and images can also be reviewed at any time and studied repeatedly to solve some thorny issues."

It is worth noting that the construction foundation pits of this project all exceed 5 meters in depth, with the deepest nearly 20 meters, making safety monitoring a top priority. "Small underground changes are difficult to detect with the naked eye, so we have deployed a monitoring network for this purpose," He Lü said, pointing to small silver instruments on the underground concrete pillars. For example, an axial force meter is installed every 40 meters in the foundation pit to monitor changes in the supporting axial force of the pit during construction.

Because the project site is only 15 meters from the Haitang River at its closest point, sufficient water level gauges have also been installed on site to ensure groundwater level safety. It is reported that various monitoring devices underground at the project are responsible for more than 10 types of monitoring items, and monitoring data are summarized and analyzed daily to ensure construction safety.

Today, the project site no longer has any "hidden corners," and the project is striving to be completed by the end of 2025, while preliminary work for Phase II and Phase III is being carried out simultaneously.

In the future, multiple high-end shopping and commercial complexes such as Taikoo Li and Super MixC will open in the Haitang Bay area, and by then the flow of people and vehicles in the area will increase significantly. The commissioning of this project will connect Haitang South Road and Haitang North Road, effectively alleviating traffic pressure and improving traffic efficiency.