New path for future urban development: Exploring diverse and composite utilization of underground space

Editor's note: Zhu Wenhui is the chairman of China Southwest Geotechnical Investigation & Design Institute Co. and China Construction Underground Space Co. The article reflects the author's opinion and not necessarily the views of CGTN. It has been translated from Chinese and edited for brevity and clarity.

As urbanization progresses, Chinese cities are experiencing rapid growth in terms of the development and utilization of underground space.

In 2021, the world's largest comprehensive underground space utilization project, the Xi'an Happiness Forest Belt Project, commenced operations with a total investment exceeding 24 billion yuan ($3.3 billion) and an underground development area of 920,000 square meters. 

By the end of 2022, the cumulative floor area of underground space in Chinese cities had reached 2.962 billion square meters. As of the end of 2023, China's total operating mileage of urban rail transit lines had exceeded 10,000 kilometers.

Underground space is extensively utilized across various urban sectors, including transportation, municipal services and commerce. It has effectively optimized the spatial structure of cities and simultaneously served as an effective measure to alleviate various "city diseases." 

To address the issue of parking difficulties in core areas and old residential communities in the cities, underground intelligent automated multi-level garages can be constructed by utilizing the underground space in urban peripheral areas and park green spaces.

For instance, the Hangzhou Miduqiao underground intelligent automated multi-level garage has a depth of 34.20 meters and spans 19 floors. The garage occupies an area of 150 square meters and accommodates 112 parking slots, with each requiring only about 1.3 square meters. Compared with traditional methods, this approach saves over 80 percent of land resources.

In response to the insufficient logistics space in core areas of the cities, the development of underground warehousing and logistics systems can help address urban logistics distribution challenges.

For example, the comprehensive underground transportation system constructed in the Rongdong District of Xiong'an New Area is about 10 meters tall in total and has two floors. The upper floor is a logistics channel capable of accommodating autonomous vehicles for logistics distribution, while the lower floor serves as a "dormitory" for pipelines of various municipal supporting infrastructure such as water, electricity, gas, heating and networks.

To address natural disasters such as urban flooding caused by extreme rainfall, underground deep tunnel drainage systems can be constructed to effectively tackle the current issue of inadequate drainage capacity of cities.

For example, with an average burial depth exceeding 30 meters, a maximum burial depth of over 60 meters and a total length of 17.5 kilometers, the Dadonghu Deep Tunnel Project in Wuhan, Hubei Province, is the largest deep tunnel for wastewater transmission in China in terms of flow capacity and distance covered.

As the urban underground space develops by leaps and bounds, numerous issues and challenges arise, such as unclear ownership of underground space, the need for breakthroughs in engineering technology and equipment, and insufficient safety operation and maintenance of underground space.

Ownership of underground space

Regarding the ownership of underground space, current issues include the unclear delineation of the operating rights and ownership of underground space, unclear legal entities, and inconsistent management standards. There is still a lack of legal basis for defining, transferring, acquiring, registering, and protecting rights in underground space. 

In recent years, big cities such as Beijing, Shanghai, Hangzhou, and Chengdu have successively enacted management regulations for the development and utilization of urban underground space, providing good examples for establishing a sound legal framework related to underground space, and encouraging social capital to actively participate in the development and utilization of underground spaces.  

Engineering technology and equipment

As for engineering technology and equipment, there are still weaknesses in engineering technology and equipment that can adapt to the demands of super-deep, large-scale, long-distance, and fast urban underground space construction and development. In particular, the international competitiveness of construction equipment for deep underground space is low, and the industrial chain is yet to be completed. 

In recent years, leading enterprises such as China State Construction and China Railway Construction Corporation Limited (CRCC) have made promising progress in technological research in ultra-deep vertical shaft construction equipment for urban areas. For example, both the Shaft Excavation Cutting Machine (SECM) independently developed by China State Construction and the "Dream" shaft roadheader independently developed by CRCC are capable of constructing super-deep vertical shafts exceeding 100 meters in urban scenarios.

Safety and maintenance

In terms of safety operation and maintenance, since urban underground space is relatively closed and has only a few entrances and exits, they exhibit traits such as strong spatial enclosure, a lack of natural light and reference objects and restricted airflow. As a result, they face evacuation and rescue challenges during disasters such as fires, water damage and earthquakes over prolonged operations. 

Currently, first- and second-tier cities in China are promoting comprehensive geological surveys and investigations to ascertain geological information up to 50 meters below the urban surface, including geological structures, underground water reserves, and geological hazards. This initiative aims to establish transparent cities and lay the groundwork for scientific development and utilization as well as safe operation and maintenance of urban underground space.

Underground space is a crucial strategic resource of China, a pivotal tool in alleviating "metropolitan diseases", a key carrier supporting green and low-carbon development, and a crucial breakthrough point for enhancing urban quality and propelling urban renewal. 

The rational development and utilization of underground space are primary tasks for the high-quality development and construction of Chinese cities and will undoubtedly chart a new course for the country's urban development.