(December 16, at Changchun Yuan in Ziyang District, Yiyang City, workers operate cluster high-pressure jet grouting concrete cutoff wall machinery to grout on the Zijiang River levee. Photo by correspondent)
Meng Jiaoyan, Hunan Daily all-media reporter; Meng Xiong and Zhou Xuan, correspondents
It is the good season for winter water conservancy repairs. On December 16, at Anzao Yuan in Anxiang County by the West Dongting Lake, 65-year-old villager Wen Guixiang, after lunch, walked up the flood-control levee from time to time to gaze at the Hongwei Sluice of Anzao Yuan, which is being rebuilt.
This is an old sluice that has been in use for nearly 50 years, only a dozen or so meters from Wen Guixiang's home. Under the "baptism" of high-level floods during this year's flood season, the Hongwei Sluice developed seepage, and villagers and officers and soldiers worked together to repair and plug the danger. "The sluice gate, which the common people call 'Chaotiankou' (facing-heaven mouth), ensures safety during the flood season and irrigation in winter." Wen Guixiang hopes the Hongwei Sluice will be repaired soon.
At present, the national major water conservancy project—the first phase of the Dongting Lake key yuan levee reinforcement project (hereinafter referred to as the reinforcement project)—has ushered in a construction climax. Structures crossing the levee, including the Hongwei Sluice, as well as slope protection, toe protection, and levee body and foundation seepage control projects, are being implemented in an intense and orderly manner. During construction, processes such as piling and pouring go deep into the levee body and foundation; this is a "hidden works," and the people of the lake area are very concerned about whether the levee can withstand the test.
Can "hidden" become "transparent"? How can the levee be made impregnable? Hunan Daily all-media reporters visited key yuans such as Anzao Yuan, Changchun Yuan, and Lannihu Yuan of Dongting Lake.
First large-scale "wall building," with higher flood-control design standards
(December 16, at Anzao Yuan in Anxiang County by the West Dongting Lake, the Hongwei Sluice of Anzao Yuan is being rebuilt. Photo by correspondent)
Anzao Yuan is located within Anxiang County, Changde. The yuan is surrounded by water on three sides, bordering the Songzi River to the west, the Hudu River to the east, and Gong'an County of Hubei to the north. As one of the 11 key levee yuans in the Dongting Lake area, it is a flood-control focus every year.
Villager Wen Guixiang of Anzao Yuan told reporters on the levee that the 1998 breach of the Anzao Yuan levee, and the 19-day joint battle by soldiers and civilians to close the breach, are still vivid in her memory.
Historically, the formation and reinforcement of levee yuans has been a long and complex process. Water conservancy expert and special researcher of the Counselors' Office of the Hunan Provincial Government Xu Gui told reporters that most Dongting Lake levees were gradually built up on sandbars and mudflats. The soil used for levee construction was all obtained locally, the levee body soil quality was poor, and due to the conditions at the time, construction basically relied on manual filling, so the filling quality was generally not high.
In the "First and Second Phase Governance of Dongting Lake" carried out from 1986 to 2010, the 11 key yuans underwent danger-elimination and reinforcement governance.
"At that time, due to investment constraints, the governance focused mainly on bringing levee cross-sections up to standard and clearing hidden dangers and rectifying risks. The front-line levees performed meritoriously in defending against floods in 2014, 2017, 2020, and other years, but still exposed many problems, especially prominent seepage in the levee foundation and levee body," Xu Gui said.
To ensure the flood-control safety of key yuans, the state arranged in 2022 to launch the first phase of the Dongting Lake key yuan levee reinforcement project, initially carrying out systematic governance of 658 kilometers of front-line levees in six key yuans: Songli, Anzao, Yuanli, Changchun, Lannihu, and Huarong Hucheng Yuan.
Wang Daoyong, professional chief engineer of Hunan Provincial Water Resources and Hydropower Survey, Design, Planning and Research Institute Co., Ltd., said that compared with the "First and Second Phase Governance of Dongting Lake" reinforcement, this reinforcement project has higher design standards. It is worth mentioning that this reinforcement project applies cutoff wall construction on a large scale, with a work volume of 7.17 million square meters. "It is like building an underwater Great Wall," Wang Daoyong said.
Multiple innovative technologies applied according to different geological conditions
On the Songzi flood channel levee of Anzao Yuan, the reporter saw a TRD (Trench Cutting Remixing Deep Wall) device, about the same "size" as a large crane, inserting a cutting box into the ground, cutting vertically, and advancing in a straight line. A pipe at one end of the cutting box injects cement slurry into the foundation, fully mixing and stirring it with the original foundation soil. In about 30 minutes, a cement cutoff wall of uniform thickness of 0.4 meters is formed 20 meters underground.
"The TRD method was mostly used in municipal construction projects in the past; this is the first time in China that it has been applied on a large scale to levee reinforcement projects," Wang Daoyong said. Dongting Lake has many levees. The cement-soil cutoff wall technology previously used generally did not exceed 18 meters in wall depth, and the quality at the joints between piles was not easy to control. The TRD method can achieve wall depths of more than 30 meters and has good continuity.
Construction site conditions change constantly. The reinforcement project selects appropriate seepage-control technologies according to different strata, different depths, and construction conditions. Wang Daoyong said that the large-scale application of new technologies such as TRD cement-soil cutoff walls and plastic concrete cutoff walls can effectively solve the seepage-control difficulties of deep permeable strata in the lake area.
On the Xiangjiang River levee of Lannihu Yuan in Xiangyin County, the reporter saw trenching machines running at full power, digging deep trench holes in the levee body, then using hydraulic grabs to take out the original soil and replace it with plastic concrete, forming a seamlessly connected cutoff wall.
"This is the plastic concrete pouring technology, which is more suitable for the geological conditions of the Lannihu Yuan levee foundation," Wang Daoyong said. This technology can greatly reduce stress within the wall and adapt to levee body deformation.
Up to now, the first phase of the Dongting Lake key yuan levee reinforcement project has completed more than 60% of the total progress. The project has produced remarkable results after implementation and played an important role in this year's flood season. Compared with historical danger situations, the levee danger occurrence rate has been reduced by more than 90%. The person in charge of the Ziyang District Water Resources Bureau of Yiyang City introduced that the Zijiang River levee in Xinqiaohe Town, Ziyang District, has historically been a concentrated point of dangers. This year, a plastic concrete cutoff wall about 30 meters deep, 0.4 meters thick, and 13 kilometers long was built, effectively avoiding dangers.
"Clairvoyance" and "wind-ear" take the field, turning "hidden works" into "transparent and visible"
On December 16, at Changchun Yuan in Ziyang District, Yiyang, the reporter saw a cluster high-pressure jet grouting concrete cutoff wall machine grouting on the Zijiang River levee.
"Most reinforcement projects are 'hidden works'; we cannot act blindly and must use wisdom," said Ouyang Jun, professional chief engineer of the Hunan Provincial Water Resources and Hydropower Design Institute. Grouting is a truly "hidden works"; grouting pressure, flow rate, inclination, and other factors must not deviate, otherwise seepage-control quality will be affected. He opened an APP installed on his phone, and data such as drilling depth, speed, and pressure of the equipment were clear at a glance.
"The secret is that sensors are installed on the drill bit of the equipment, which can record data in real time. Once the data deviates, an automatic alarm will be issued," Ouyang Jun said.
The reporter came to the reinforcement project department in Heshan District, Yiyang City—the "smart brain" of the project. Supervisory personnel opened the smart construction site platform, and the project construction situation was fully visible.
Ouyang Jun introduced that focusing on the two major cycles of construction and management, the project innovatively uses technologies such as BIM (Building Information Modeling) and IoT+, independently researches and develops manufacturing system platforms and IoT wearable devices, and creates a digital twin levee yuan. Up to now, the coverage rate of information-based front-end supervision equipment for key processes and methods has exceeded 98%, and more than 25 million pieces of various construction supervision information have been collected.
In addition to real-time monitoring of piling and grouting, through the smart construction site platform, the reporter also saw the power of "black technology" in different scenarios.
As the most basic project, the riprap toe protection project requires a large number of ships or trucks to transport stones to designated locations and dump them during construction. Now, high-definition cameras are installed on transport ships and trucks, and the quantity and quality of stones are clear at a glance on the computer, effectively preventing cutting corners.
Termite control uses "digital bait." The levee sections with termite problems in the six key yuans total nearly 160 kilometers, a major governance challenge. Researchers installed alarm devices on the bait to attract termites to feed; during feeding, the termites trigger the device and send a signal.
The reporter saw that mobile video stations are installed at the construction site, and the positioning of workers can be accurate to the centimeter level. "The entire reinforcement project has many points and long lines, but work is not carried out simultaneously. Developing mobile video stations is aimed at reducing costs and increasing efficiency, using funds where they are most needed," Ouyang Jun said. With these "clairvoyance" and "wind-ear" devices taking the field, the construction process has achieved all-round and whole-process supervision, turning "hidden works" into "clear works."
It is reported that the reinforcement project aims to complete the main works before the end of 2025. At present, the second phase of the reinforcement project is undergoing feasibility study report evaluation. Experts believe that the digital supervision methods of the first phase of the reinforcement project have explored a scientific, standardized, and sustainable quality construction and management method for subsequent Dongting Lake governance.
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