On the morning of August 18, the first shield machine for the Wuhan Dadonghu Core Area Sewage Transmission System Project was launched, marking the entry of this deep sewage transmission tunnel into the tunneling phase. Customized Small Shield Equipment
The main tunnel of the Dadonghu Core Area Sewage Transmission System Project is 17.5 kilometers long, spanning Wuchang District, Hongshan District, Qingshan District, and East Lake Scenic Area. It is currently the deep sewage tunnel with the largest transmission flow and the longest transmission distance in China, and the first to adopt a fully underground sewage pretreatment station in the main urban area.
According to the construction manager, this ultra-long deep tunnel has 9 shafts and 9 shield-driven sections, with shaft depths ranging from 32 meters to 51.5 meters. The tunnel is equivalent to a "special subway" that directly transports sewage to the treatment plant for centralized processing. Yesterday's shield launch point was located at Shaft No. 3, which is 34.9 meters deep and serves as a bidirectional launch shaft. The shield machine will first tunnel from Shaft No. 3 to Shaft No. 2 and then to Shaft No. 1, covering a length of 3.16 kilometers; afterwards, it will turn and continue tunneling.
Since the tunnel diameter of this deep sewage system is 3 to 3.4 meters, with a cross-sectional area only a quarter of that of a conventional subway tunnel, and the burial depth is twice that of a subway, traditional shield machines are not suitable. In addition, the shield-driven sections face numerous difficulties: they must pass through a 970-meter-long moderately weathered limestone section, and 550 meters lies beneath the bottom of Yanxi Lake where karst caves are dense, making the shield machine prone to "dipping"; the tunnel also passes under subway lines, buildings, and elevated bridges. Therefore, the construction party collaborated with shield machine manufacturers to customize top-tier small shield equipment in China. During operation, the shield machine, with a total length of over 120 meters and divided into 18 sections, is disassembled and connected via pipelines, distributed underground and on the surface, gradually lowered into the shaft for tunneling, and then reassembled underground to achieve full-machine tunneling.
Construction Like Making a Swiss Watch
According to reports, when the tunnel operates in the future, it must withstand both the pressure of groundwater and the pressure of internal sewage, so the construction requirements are extremely high. During high-pressure transmission, it must be like a completely sealed water pipe, with no pores or tiny cracks allowed. We call this building a "Swiss watch" in the construction industry. To this end, construction personnel used ultra-long-distance vertical and horizontal concrete pumping to ensure the forming quality of the concrete; for the first time, they carried out synchronous construction of small-diameter shield segments and secondary lining concrete structures, and the inner side of the secondary lining is coated with a surface coating to achieve corrosion resistance, ensuring that water inside and outside the tunnel does not interfere with each other.
After the deep tunnel project is completed, it will integrate the three existing sewage treatment plants in the Wuchang area—Shahu, Erlangmiao, and Luobuzui—and the under-construction Beihu Sewage Treatment Plant into a "four-in-one" system. By then, sewage from half of Wuchang City north of Wuluo Road and the surrounding areas of the East Lake core area will be rapidly transported through the "special subway" to the Beihu Sewage Treatment Plant. In the near term, it can achieve a sewage treatment scale of 800,000 tons per day, and in the future, it will reach 1.5 million tons per day, serving a population of 3 million. This will help alleviate the contradiction between the land layout of urban sewage treatment plants and the urban development pattern, and at the same time optimize the layout of urban sewage facilities. In addition, during moderate to heavy rain, it can also perform regulation, storage, and drainage functions.