In June 2009, the State Council Executive Meeting discussed and approved the "Hengqin Overall Development Plan," committed to building Hengqin in Zhuhai, Guangdong into an "open island," "dynamic island," "smart island," and "ecological island."
The Hengqin New Area has a total area of 106.46 square kilometers, but only 28 square kilometers are developable, making the available land resources quite scarce. For Hengqin, how to efficiently use the limited land resources is an important issue to consider in development. Building an underground utility tunnel has become one of the local methods for economical and intensive land use.
After the Hengqin underground utility tunnel was completed, the project, as a model project for utility tunnels, was promoted nationwide. In April 2015, the Ministry of Housing and Urban-Rural Development organized mayors from more than 70 cities nationwide and over 300 experts and scholars to visit and learn on-site, promoting the development and construction model and experience of the Hengqin underground utility tunnel.
As a model for new city construction, what difficulties did the Hengqin underground utility tunnel encounter during construction, and how were they solved? What benefits has its operation brought to the Hengqin New Area?
Swinging a Sledgehammer on "Jellied Tofu and Tidal Flats"
The Hengqin underground utility tunnel started construction in May 2010, completed its main structure by the end of 2013, and was fully operational in early 2014, with an astonishing construction speed. However, few people know that the area below the utility tunnel is mostly tidal flats and fish ponds, with an average mud thickness of 25m and a maximum depth of over 41.5m. Some areas also have block stone layers 5-10m deep; the soft is very soft, and the hard is even harder, making construction extremely difficult.
MCC Group is the investor of the Hengqin underground utility tunnel, and China MCC20 Group is the general contractor. As the chief engineer of the Guangdong Branch of MCC20 Group, Xu Haiyan participated in the core design and construction of the Hengqin underground utility tunnel. He was deeply impressed by how to build this huge concrete structure on Hengqin's "jellied tofu and tidal flats."
"The mud here has poor characteristics and is more prone to settlement under load," Xu Haiyan said. In addition, the high sensitivity of the mud makes it difficult to smoothly complete the construction processes of excavating the foundation pit, piling, and supporting, "like inserting a stick into mud; initially there is some resistance, but if you wiggle it, the resistance drops significantly."
To address this, the construction party adopted the drainage consolidation method: inserting drainage boards into the mud, adding surcharge on top to increase load, and with the help of vacuum pumping equipment, draining the water from the mud through the drainage boards, allowing the mud to gradually consolidate and increase in strength. Ultimately, the average moisture content of the soil was successfully reduced from over 65% to 45%.
Saving 400,000 Square Meters of Land
Generating Direct Economic Benefits of 8 Billion Yuan
"According to preliminary estimates, the construction of the entire underground utility tunnel in Hengqin saves about 400,000 square meters of urban construction land," said Yan Lisheng, deputy general manager of Zhuhai Da Hengqin City Utility Tunnel Operation Management Co., Ltd. The utility tunnel achieves a "three-dimensional layout" of pipelines, replacing the traditional "planar staggered layout." The pipeline layout is compact and reasonable, reducing the area occupied by underground pipelines below and on both sides of roads, significantly saving urban land.
Although the one-time construction cost of an underground utility tunnel is relatively high, the later benefits are very significant. "Practice has proven that the value generated by this decision far exceeds expectations," said a relevant person in charge of the Zhuhai Construction and Environmental Protection Bureau in an interview with the media. "According to statistics, the land saved by building the underground utility tunnel in Hengqin, combined with the current comprehensive land price and urban floor area ratio of Hengqin, is estimated to generate direct economic benefits of more than 8 billion yuan."
Saying Goodbye to "Road-ripping"
Pipelines Entering the Tunnel Takes Only Two Days
The underground utility tunnel centrally lays municipal pipelines such as electricity, communications, broadcasting, water supply and drainage, heating, and gas in a public tunnel.
In the past, each pipeline owner directly buried pipelines underground. Once a pipeline needed repair or relocation, the city road had to be repeatedly excavated, creating "road-ripping" in the city. But if a city has an underground utility tunnel, it is equivalent to building a common "home" for pipelines underground. Other pipelines only need to pay "rent" to "move in," without excavating themselves. In this way, the city can say goodbye to "road-ripping" and reduce the impact and interference on traffic and residents' travel caused by frequent excavation.
After pipelines enter the tunnel, pipeline users immediately feel the benefits. Yan Lisheng once gave a simple example: as the population density of Hengqin increases, the weak current pipelines of operators such as telecommunications and mobile in a certain area are insufficient, and new optical cables need to be added. At this time, if the past method of direct burial is used, it would take at least four to six months for the operator from planning the route to applying and completing construction. If the pipeline enters the tunnel, adding an optical cable is just like adding a "tenant" to the house; the entire process of handling procedures and putting the optical cable into the tunnel takes only two days.
The Hengqin utility tunnel is also ahead in intelligent construction. Various urban pipelines are deeply hidden in underground enclosed spaces. How to ensure safety, facilitate inspection, and ensure the linkage of equipment within the tunnel is the essence of a smart utility tunnel. After multiple comparisons, China MCC20 Group invited Zhongmeng Technology, a representative enterprise in domestic smart utility tunnels, to participate in the construction. To prevent various safety incidents, various intelligent subsystems have been built inside the Zhuhai Hengqin utility tunnel, including video surveillance systems, environmental monitoring systems, access control systems, intrusion alarm systems, etc. At the same time, on top of these systems, Zhongmeng Technology specially developed a smart utility tunnel information management platform.
Zheng Jianming, head of the R&D department of Zhongmeng Technology, said, "The information management platform of the Hengqin utility tunnel allows each subsystem to interact and interconnect information while operating independently, automating event processing and forming integrated prevention and control and one-stop management." The Zhuhai Hengqin utility tunnel is also an urban utility tunnel with a very high degree of informatization and automation.