Today, for urban development, the utilization of land resources has long extended beyond the flat plane to three dimensions. As a result, the development and use of underground space is receiving increasing attention.

The 2023 National Natural Resources Work Conference proposed encouraging three-dimensional development of above-ground and underground space, using "underground" in exchange for "above-ground." Data from the 2021 Blue Book on China's Urban Underground Space Development shows that the Yangtze River Delta city cluster and the Pearl River Delta city cluster within the Guangdong-Hong Kong-Macao Greater Bay Area together constitute the growth pole leading China's urban underground space development. 

Data shows that as early as 2020, the newly added underground space floor area in China's eastern region increased year-on-year, with a growth rate of 3.78%, most notably in Zhejiang, Jiangsu, and Shanghai. Data from the Shanghai Municipal Planning and Natural Resources Bureau shows that Shanghai's underground space has entered a period of rapid development, and a polycentric, networked underground space development pattern has basically taken shape in the central urban area. 

In the process of developing a "future city" that grows downward, how can scientific planning and rational utilization be achieved, and the potential of underground space resources be released in a step-by-step manner? What difficulties and challenges will be encountered? Shanghai's experience may offer useful reference for answering these questions of urban development.

Potential Resources

Frequent Highlights in Underground Space Development 

In March 2023, the hubo commercial street—an underground passage connecting the Shanghai Hongqiao Comprehensive Transportation Hub and the National Exhibition and Convention Center—made its debut. It not only added diverse and colorful business formats to this over-1,000-meter transportation support project for the China International Import Expo, which had already opened at the end of 2019, but also provided a convenient, super-sized commercial space for citizens working and living nearby. Commuters who used to hurry past now slow their steps, taking a fresh look at this weatherproof underground transportation corridor and incorporating it into their shopping, social, and daily life scenarios.

Hongqiao Tiandi hubo, located in the underground hub of Hongqiao Railway Station. Photo courtesy of Hongqiao Tiandi.

"In areas developed as contiguous tracts, such as new city development and urban renewal, the integrated development model of underground space is favored by the government and developers," said He Yaochun, a planner at the Shanghai Urban Planning and Design Research Institute. "For large-scale projects like the Hongqiao Hub-NECC, the principle of integrated planning and phased development of underground space was established from the very beginning of planning, and implementation was advanced step by step from design to construction to management, maximizing interconnection and efficient sharing of functional facilities in underground space. This measure not only reduces development costs but also facilitates the economical and intensive use of spatial resources," He Yaochun said.

If the integrated planning and development of underground space provides more room for imagination for the city's future development, then scattered idle underground spaces offer resource potential and innovative ideas for the micro-renewal of Shanghai's old residential communities.

In March 2023, "Xianxialai Cooperative" made its debut in the Xianxia Road community of Changning District, Shanghai. The site of this small yet beautiful community renewal project was a civil air defense facility that had been idle for over a decade. After renovation, the 1,100-square-meter underground space was partitioned into 36 cubicles, including activity spaces for community residents' leisure, as well as entrepreneurship spaces and time-shared spaces for entrepreneurs. It is warm in winter and cool in summer, well-designed and decorated, with many novel shops—nothing like the dilapidated underground cave it once was. Residents are very satisfied with this "multifunctional living room" near their homes, and since the cooperative opened, the number of visitors has grown day by day.

Underground supermarkets, underground parking lots, underground warehouses, underground logistics, underground municipal facilities... In densely populated Shanghai, where land is worth its weight in gold, underground space resources have become the "prescription" for solving the space congestion problem brought by "urban diseases," optimizing functional layout and improving urban resilience.

In 2010, at a depth of 31.5 meters beneath Jing'an Sculpture Park, the Shanghai Expo Jing'an Substation was officially put into operation, becoming China's first 500 kV underground substation and the world's largest and most technologically advanced 500 kV underground substation. In 2019, the Shanghai Zhuguang Road Passage—then China's largest earth pressure balance shield tunneling project—officially opened to traffic; the project was the first in China to adopt "fully prefabricated assembly" for a super-large-diameter shield tunnel. In 2021, the deepest foundation pit project in Shanghai—the Yunling West section shaft of the Suzhou Creek Deep Drainage and Storage Pipeline System Project, reaching a depth of 58.65 meters—was successfully completed with its base sealed, advancing Shanghai's sponge city construction another step. In 2022, Shanghai's first vertical excavation (shield) underground smart garage project—the deep shaft parking garage in Daning Subdistrict, Jing'an District—officially began excavation. The excavation diameter of a single shaft reaches 23.02 meters, currently the world's largest-diameter shaft; once completed, it will provide 304 parking spaces, effectively alleviating the long-standing "parking difficulty" pressure in the subdistrict.

Over the past five years, Shanghai has comprehensively carried out the work of burying overhead lines underground and consolidating utility poles, accelerating the construction of underground utility tunnels, and freeing up more ground space for parks and greenery.

Threefold Challenges

Safety, Order, and Efficiency

Shanghai's underground space development began with civil air defense engineering construction in the 1960s. Since the 1990s, with large-scale old city renovation, new area construction, and rail transit construction, the scale of Shanghai's underground space development has expanded rapidly.

As of March 28, 2023, Shanghai had a total of 43,168 underground projects, with a total area of nearly 150 million square meters, mainly divided into three categories: production and living service facilities, public infrastructure, and rail transit facilities. Among them, the Shanghai Metro (including Shanghai and the Shanghai metropolitan area) is the world's longest urban rail transit system. Large-scale underground space development has made up for the shortfall in urban spatial resources, making Shanghai one of the cities with the largest scale of underground space development in China, but a series of accompanying problems have gradually emerged.

"The most important thing in underground space development is safety," said Shi Yujin, chief expert at the Shanghai Institute of Geological Survey. As a coastal city, Shanghai faces two major problems in underground space development: groundwater and soft soil. Foundation pit excavation and tunnel construction in soft soil areas have very high technical requirements; if the design scheme is unscientific or measures are improper, it can cause groundwater leakage, resulting in quicksand, slope instability, and large-area ground collapse. This means the cost and risk of underground space development in Shanghai are higher. "Especially for the development of deep underground space resources below 50 meters—although there are few cases at this stage, as deep development continues, how to ensure construction safety, environmental safety, and subsequent operational safety poses new challenges to existing underground engineering technology," Shi Yujin explained.

The timing sequence of underground space development at different depths is equally important. Shallow underground space within 15 meters in Shanghai's central urban area is approaching saturation; current development is mainly concentrated in the middle-layer underground space of 15 to 30 meters, and some major projects have development depths exceeding 30 meters. Underground rooms, pile foundations, various pipelines, underground passages, and tunnels of various buildings outline the crisscrossing and complex form of underground Shanghai. Already-built underground space facilities are difficult to relocate, and renovation is also very difficult, often significantly affecting newly planned facilities and becoming a constraining factor for further optimizing spatial layout.

Compared with the central urban area, where underground space is fully developed and utilized, suburban areas have less demand for underground space development. Once above-ground construction projects are completed, it becomes very difficult to develop underground space afterward. In the long run, this is not conducive to the economical and intensive use of urban spatial resources.

Some underground spaces that are disorderly developed, outdated in design, or subject to fragmented management also suffer from low utilization efficiency. Due to the lack of overall planning and limited understanding of underground space resources, many underground structures built in Shanghai in the early period are independent units that are not interconnected, with relatively single functions, and now clearly cannot meet the needs of high-quality urban development. In addition, due to different development depths, the renovation difficulty and cost of existing underground structures are relatively high. Over time, the utilization efficiency of these scattered underground spaces has gradually decreased, and some have become idle resources.

In addition, various underground pipelines with multiple construction entities are difficult to govern due to complex ownership, use rights, and management rights, and also pose many hidden dangers of public accidents.

Blueprint

Scientific Planning Hand in Hand with Institutional Development 

In response to the above problems, Shanghai has actively responded through conceptual breakthroughs, planning first, technological research, and institutional innovation, continuously seeking optimization solutions. In the course of underground space development and utilization spanning decades, Shanghai has not only created many classic cases but also gradually formed systematic supporting policies and rich management experience.

Shanghai was the first city in China to carry out underground space planning. As early as 2003, it compiled the "Shanghai Underground Space Conceptual Plan," determining the principles, objectives, and overall layout of Shanghai's underground space planning, and giving play to the guiding and controlling role of planning. The "Shanghai Underground Space Planning Compilation Guidelines" issued in 2008 improved the underground space planning compilation system, clarifying the content, depth, and approval procedures for underground space planning compilation, as well as relevant requirements for underground space planning in key areas. Subsequently, Shanghai successively compiled the "Shanghai Underground Space Near-Term Construction Plan (2007-2012)," the "Shanghai Urban Rapid Rail Transit Near-Term Construction Plan (2010-2020)," the "Shanghai Comprehensive Transportation Hub Near-Term Site Selection Plan," the "Shanghai Central City Public Green Space Plan," the "Shanghai Civil Air Defense Engineering Professional Planning Outline," the "Shanghai Civil Air Defense Backbone Engineering Layout Plan," and a large number of detailed underground space plans for key areas. Districts including Huangpu, Luwan, Baoshan, Hongkou, and Jiading also compiled district-level underground space plans. The "Shanghai Urban Underground Space Development, Utilization, and Protection 12th Five-Year Plan," formulated in 2012, proposed the guiding principle of "coordinated planning, orderly development, rational utilization, and effective protection." With the implementation of the "Shanghai 2035 Master Plan," a new round of special underground space planning is being compiled. In November 2020, the "Shanghai Lin-gang Special Area Underground Space Planning and Design Guidelines (Trial)" was released, proposing for the first time guiding underground space planning and design according to the systematic functional requirements of an underground city, planning to form a networked underground space of "one core, three axes, and multiple nodes," and achieving vertical layering, horizontal connectivity, and organic growth of underground space. In March 2021, the "Shanghai New City Planning and Design Guidelines" was released, proposing large-scale development of underground space and the construction of "underground cities," and setting key indicators such as "underground building volume in key areas reaching about 50% of above-ground building volume; the proportion of new municipal facilities (including substations, drainage pumping stations, garbage transfer stations, etc.) built underground reaching 100%."

Shanghai is also the first city in China to carry out urban underground space resource surveys and evaluations. As a pilot unit for the clustering of national geological data and information, the Shanghai Institute of Geological Survey has, since 2009, continuously carried out initial surveys of underground space across the city, comprehensively and accurately ascertaining spatial information such as the "four boundaries," shape, burial depth, and use of developed and utilized underground space in Shanghai, and establishing a citywide underground space basic database, providing solid technical support for underground space planning, land use approval, and underground cadastral management.

"By integrating massive geological borehole data, monitoring data, and underground space survey data, we can visually see the complete underground world within 200 meters below the central urban area and within 100 meters below the entire city in the form of 3D models. This means we can give more scientific and precise evaluations of the quantity and quality of underground space resources at different levels, and conduct risk assessments and development recommendations for site selection and construction of deep underground space construction projects," Shi Yujin said. Based on different geological conditions, the institute proposed use control zoning for underground space development, dividing the entire city into prohibited development zones, restricted development zones, and suitable development zones for underground space. In the site selection of underground projects such as the North Henggang Passage, this visual data system played an important role, not only making it convenient to consider avoiding existing underground buildings (structures) in advance during project planning, but also enabling comprehensive and accurate assessment of the demolition volume of buildings (structures) during project implementation.

Technicians operating a backpack laser radar 3D scanning system at the entrance and exit of an underground garage. Photo courtesy of the Shanghai Institute of Geological Survey.

In terms of underground space management, Shanghai has actively explored and issued a series of laws, regulations, and management systems. Since 2010, it has not only established a citywide joint conference system for underground space management to strengthen collaborative management among relevant departments, but also promulgated and implemented a series of regulations including the "Shanghai Underground Space Safe Use Management Measures," the "Shanghai Land Subsidence Prevention and Control Management Regulations," and the "Shanghai Underground Space Planning and Construction Regulations," requiring that underground space development should follow the principles of coordinated planning, comprehensive development, rational utilization, safety and environmental protection, giving priority to public interests, and coordination between underground and above-ground, and that underground space should be utilized in layers. In 2013, Shanghai issued the "Shanghai Urban Underground Space Construction Land Approval and Real Estate Registration Provisions," strengthening underground space cadastral management, proposing targeted policy recommendations for the establishment and confirmation registration of rights for different types of underground space, and reserving technical methods for the confirmation and registration of real estate rights for spatial resources. The "Shanghai Underground Construction Land Use Right Grant Provisions" issued in the same year clarified that the use right of commercial underground construction land shall be subject to a paid use system, and determined the land price calculation rules for underground space according to the principles of "encouraging development, layered utilization, distinguishing uses, and coordination between underground and above-ground."

During the 14th Five-Year Plan period, Shanghai proposed accelerating the planning and construction of new cities. In the construction plans for the "five new cities" of Jiading, Qingpu, Songjiang, Fengxian, and Nanhui, Shanghai strengthened the important role of underground space in improving urban resilience, laying out smart infrastructure, and enhancing disaster prevention capabilities. As a non-renewable natural resource, underground space resources—especially deep underground space resources—have received increasing attention and concern from government departments and the public regarding their orderly development and rational protection.

With the advancement of the construction of Shanghai's "five new cities," new concepts such as resilient cities, sponge cities, and three-dimensional cities, as well as new technologies such as digital twin cities, are painting a picture for people of a safe, orderly, eco-friendly, efficient, intelligent, interconnected, and fully functional future underground city. For example, Lin-gang New City is vigorously promoting the construction of a digital twin city based on underground space. As of the end of 2022, the digital twin city had completed the construction of basic base maps including 5,390 underground structures and 6,343.7 kilometers of underground pipelines. It is expected that by 2025, the Lin-gang New City digital twin city basic platform will be initially completed, possessing platform-level support capabilities for key application scenarios and achieving "integration of above-ground and underground, and integrated growth of reality and planning."

Surveyors re-measuring the axis of the Shanghai Metro. Photo courtesy of the Shanghai Institute of Geological Survey.

In addition, Shanghai will further rationalize the underground space management mechanism, strengthen the construction of a citywide dynamic monitoring system for underground space resources and a safety early-warning system for major underground infrastructure, improve construction standards, approval processes, and management models for different types of underground space development, and enhance the application level of new technologies such as digital twin cities.

The future city growing downward is always a work in progress. Next, Shanghai will actively embrace the future and, through its own exploration, explore more possibilities for the three-dimensional development of territorial space and the economical and intensive use of land resources.