This article is selected from the journal of the Chinese Academy of Engineering, China Engineering Science, Issue 1, 2023
Authors: Wang Guosheng, Ji Hong Kong and Macao, Lu Dechun, Du Xiuli
Source: Research on low-carbon development strategy of urban underground infrastructure[J].Strategic Study of Chinese Academy of Engineering,2023,25(1):30-37.)
Editor's note
In the context of resilient cities, sponge cities and urban renewal, urban underground infrastructure, as an important part of urban construction, plays an important role in promoting high-quality urban development and helping to achieve the "dual carbon" goal in mainland China.
The research team of Academician Du Xiuli of the Chinese Academy of Engineering published an article "Research on Low-carbon Development Strategy of Urban Underground Infrastructure" in the first issue of the journal of the Chinese Academy of Engineering, China Engineering Science, 2023. This paper summarizes the current situation and existing problems of low-carbon development of urban underground infrastructure, and puts forward the implementation path and strategy of low-carbon development of new and existing urban underground infrastructure. The study concludes that for the new urban underground infrastructure, the low-carbon development strategy that comprehensively considers the whole life cycle of urban underground infrastructure in the planning and design, construction and physicalization, operation and maintenance stages is proposed, and the green transformation strategy of electrification, intelligence and practicality, as well as the convergence of the old and the new, and the green expansion strategy of harmony and difference are proposed. In order to further promote the low-carbon development of urban underground infrastructure in mainland China, countermeasures and suggestions were put forward from four aspects: finding out the greenhouse gas emission background of urban underground infrastructure, improving the top-level design of low-carbon development of urban underground infrastructure, strengthening the research and development of low-carbon development technology of urban underground infrastructure, and strengthening the policy tilt of low-carbon development of urban underground infrastructure.
I. Preface
Underground space has the characteristics and advantages of expanding infrastructure capacity, improving land utilization, saving land resources, alleviating the density of central cities, preventing traffic congestion, and increasing urban green area. Since the beginning of the 21st century, in order to solve the problem of "big city disease" and improve the operation efficiency of large cities, more and more urban infrastructure has been built underground, and the development and utilization of underground space resources have been rapidly developed in many countries and regions in the world. Japan solves the problems of limited land resources and dense population by building urban underground infrastructure such as underground utility trenches, underground roads, and underground public facilities. Montreal, Canada, has a 32 km long underground city network with the subway as the core and the pedestrian passage as the network. As of 2015, Helsinki, Finland has built nearly 10 million cubic meters of underground infrastructure with various functions such as underground parking lots, subways, coal and oil storage facilities, and comprehensive pipe corridors. In the 90s of the 20th century, Academician Qian Qihu put forward the forward-looking view that "the 21st century is the century of underground space, and underground space will be the second space for urban development". The "Special Plan for Urban Underground Space in Shanghai" (2021) proposes that in the future, urban infrastructure will be gradually transformed underground, and new municipal pipeline facilities will be prioritized for underground construction, and underground transportation infrastructure will be continuously upgraded, and the "Zhengzhou Urban Master Plan (2018-2035)" (2018) points out that it is necessary to coordinate the development of intelligent modern cities and underground facilities and improve the diversified and efficient use of underground space in Zhengzhou. In the context of resilient cities, sponge cities and urban renewal, the Opinions of the State Council on Strengthening Urban Infrastructure Construction (2013) also proposed that the principle of "planning first, then construction, underground first, then aboveground" should be adhered to in the construction of urban infrastructure, and the 13th Five-Year Plan for the Development and Utilization of Urban Underground Space, the 14th Five-Year Plan and the plans of local governments all involve the vigorous development of urban underground space.
The low-carbon development of urban underground infrastructure can focus on carbon emission and carbon sequestration, of which carbon emissions include the source end and the consumption end, so the low-carbon development of urban underground infrastructure can be developed from the "three ends" of the source end, the consumption end and the carbon sequestration end. At present, the underground construction of new infrastructure and the underground transformation of existing infrastructure have a good momentum of development, which meets the development requirements of urban renewal for the supplement of above-ground functions. Urban underground infrastructure can directly or indirectly achieve energy conservation and emission reduction, such as underground storage facilities compared with above-ground facilities, with the characteristics of constant temperature and humidity, which can directly reduce the CO2 generated by temperature and humidity control; In the field of construction and transportation, in order to achieve the goals of carbon peak and carbon neutrality, there is an urgent need to explore the low-carbon development path of urban underground infrastructure.
In order to promote the research on the low-carbon development of urban underground infrastructure, this paper summarizes the advantages of urban underground infrastructure in contributing to the "dual carbon" goal, the development status and existing problems of urban underground infrastructure, puts forward the concept, path and emission reduction technology of low-carbon development of urban underground infrastructure, and gives corresponding countermeasures and suggestions, in order to provide reference for the low-carbon development of urban underground infrastructure in mainland China.
2. The advantages of urban underground infrastructure to help achieve the "double carbon" goal
(i) Urban underground infrastructure that directly reduces emissions
The use of geothermal resources to develop urban underground infrastructure (e.g. ground source heat pumps) can achieve direct emission reductions. At present, the direct utilization of geothermal resources in mainland China is at the world's leading level, and the cascade utilization technology of geothermal resources and underground aquifer energy storage technology have been gradually developed. The annual recoverable amount of shallow geothermal energy resources within the 336 urban planning areas above the prefecture level in mainland China is about 7×108 tce, and the construction of urban ground source heat pump infrastructure can effectively help the transformation of energy structure, improve the utilization rate of renewable resources, and reduce CO2 generated by heating and cooling. Taking the ground source heat pump system in Beijing Daxing International Airport as an example, the shallow geothermal energy extracted by the system is about 5.636×1014 J per year, according to the climate of Beijing and the energy consumption characteristics of the project, the heating period in winter is usually 123 days, the cooling period in summer is 120 days, and the daily use time is 24 h, which can meet the winter heating and summer cooling needs of 2.57×106 m2 buildings, save about 1735.89 m3 of natural gas, and reduce carbon emissions by more than 3750 t. In addition, moving shopping malls in urban business districts to underground spaces can significantly reduce carbon emissions compared to the same scale of construction facilities above ground. For example, the carbon emissions of a commercial area with a construction area of 71 630 m2 can be compared with that of underground, and the construction of a commercial area with underground infrastructure can reduce carbon emissions by 2.336 t CO2 per year.
(ii) Urban underground infrastructure that indirectly reduces emissions
Some urban underground infrastructure, while not able to achieve direct emission reductions, can be achieved indirectly by serving other infrastructure. For example, underground transportation facilities can effectively alleviate traffic congestion and improve transportation efficiency. According to statistics from the Ministry of Ecology and Environment, the economic losses caused by traffic congestion on the mainland are as high as 250 billion yuan every year. The carbon emissions of the transportation industry account for about 10.2% of the country's total carbon emissions, of which road transportation accounts for about 80% of the carbon emissions of the transportation industry. In 2020, the cumulative passenger volume of Chengdu Metro was about 1.21×109 trips, and the average daily passenger volume for the whole year was 3.311×106 trips, which is equivalent to a daily reduction of 7.86×105 private car trips, and the urban public transport travel share rate exceeded 50%, which indirectly reduced carbon emissions by about 8.75×104 tons by improving passenger transport efficiency.
As an important part of the city, the development and utilization of urban underground space can effectively save land resources. For example, the underground silo intelligent parking garage built at the south entrance of Suzhou Forest Park, covering an area of only 82.7 m2, transforms the original parking space of 3 cars into 48 parking spaces, which effectively saves ground resources while alleviating the surrounding parking difficulties. During the "13th Five-Year Plan" period, the total scale of direct investment in underground space development in China was about 8 trillion yuan, and the cumulative construction area of new underground space in the country reached 1.07×109 m2, which greatly saved land resources.
(iii) Carbon sink benefits of urban underground infrastructure
Urban greening is an important part of the construction of urban ecological civilization, and it is also an important carrier that reflects the culture and connotation of the city. Using the characteristics of underground space, the infrastructure suitable for construction underground is conducive to freeing up ground space, creating a green ecological environment, and increasing carbon sinks, such as underground urban infrastructure such as rail transit, commerce, sewage treatment, garbage treatment and transfer stations and substations. The study shows that about 1.83 t CO2 can be absorbed per 1 m3 of forest volume, taking Shanghai as an example, the residential land is 549.77 km², and the land for commercial service facilities is 124.66 km², if 50% of them are transferred underground, about 337.2 km² of green space can be replaced, and if used for urban gardens, about 4.24×106 m3 of tree volume can be obtained, and about 7.76×106 t CO2 can be absorbed.
To sum up, urban underground infrastructure has the benefits of reducing emissions and increasing sinks at the source, consumption and carbon sequestration ends, which can effectively help achieve the "double carbon" goal. At the source end, geothermal resources can effectively replace some fossil energy, provide cooling and heating for underground infrastructure, and increase the proportion of clean energy consumption. On the consumer side, some underground infrastructure (such as subways and underground garages) can improve the efficiency of urban operation, thereby achieving energy conservation and emission reduction. At the carbon sequestration end, the underground space itself is enclosed, which can better complete the carbon capture work, and in addition, the development of underground infrastructure can free up the ground space, create a green ecological environment, and increase the carbon sink capacity of the natural ecosystem.
3 Current status and existing problems of low-carbon development of urban underground infrastructure
Based on the connotation of urban underground infrastructure, this paper analyzes the current situation and existing problems of low-carbon development of underground infrastructure from three perspectives: the whole life cycle of underground infrastructure, the "three-end" system planning and safeguard measures, and provides a reference for the research on low-carbon development of urban underground infrastructure.
(1) Research status of low-carbon development of urban underground infrastructure
Since the beginning of the 21st century, the development scale and speed of urban underground infrastructure in mainland China have ranked among the top in the world, and it has become a major country in the development and utilization of urban underground space in the world. According to the needs of different stages of urban development, the development of urban underground infrastructure can be divided into three stages: the stage of municipal function demand based on the construction of municipal infrastructure pipelines, the stage of transportation function demand based on urban underground rail transit, and the stage of upgrading the environment and deepening the demand stage based on the integration of aboveground and underground infrastructure. At present, small and medium-sized towns in mainland China have entered the stage of demand for municipal infrastructure functions, large and medium-sized cities have entered the stage of demand for transportation functions, and megacities have entered the stage of improving the environment and deepening demand. As of the end of 2020, the cumulative construction area of urban underground space was 2.4×109 m2, of which the construction area of new urban underground space in 2020 was 2.59×108 m2, and the new underground space construction area (including rail transit) accounted for about 22% of the completed area of urban buildings in the same period. At present, the underground infrastructure of mainland cities is dominated by underground transportation facilities and municipal infrastructure, especially the construction speed of urban rail transit has ranked among the top in the world, and the construction of urban underground expressways is in the stage of accelerated development. The Ministry of Housing and Urban-Rural Development pointed out that it is necessary to strengthen the utilization of urban underground space and the construction of municipal infrastructure, requiring that by the end of 2023, the basic completion of the facility census, the establishment of a comprehensive management information platform coverage, and the promotion of underground space informatization, stratification, and efficient utilization. The General Office of the State Council pointed out in the "Opinions on Promoting the Green Development of Urban and Rural Construction" that the level of systematization of urban and rural infrastructure should be improved, the existing infrastructure should be surveyed, the comprehensive utilization of underground space should be coordinated, and the comprehensive three-dimensional transportation of cities with perfect functions should be established. Judging from the scale of urban underground space development in mainland China and the relevant guiding policies issued by the state, the development potential of urban underground infrastructure in mainland China is huge in the future. However, there are few reports on the carbon emissions and low-carbon development pathways of urban underground infrastructure.
(2) Problems in the low-carbon development of urban underground infrastructure
1. The low-carbon development of the whole life cycle of urban underground infrastructure needs to be optimized
From the perspective of the carbon footprint of the whole life cycle of buildings, the carbon emissions in the operation and maintenance phase account for more than 80% of the total emissions, and for urban underground infrastructure, the carbon emissions in the operation phase also dominate. Since the pre-design of planning and construction has a significant impact on carbon emissions in the operation stage, the low-carbon development of urban underground infrastructure should be optimized from the whole life cycle, focusing on the operation and maintenance stage. (1) In the planning stage, there are mainly shortcomings in top-level design, such as the lack of coordination of the entire urban function at the urban scale and the aboveground and underground integration scale, the zoning of aboveground and underground functions, and the long-term spatio-temporal dual-scale design concept. (2) In the construction stage, new green building materials are rarely used, and the characteristics of the underground surrounding rock are not brought into play, and high-emission materials (such as concrete) are used too much, and intelligent construction and industrial construction technologies are rarely used in the construction process, especially the local assembly technology suitable for the construction of underground structures and the new carbon sequestration foundation consolidation technology. (3) In the operation and maintenance stage, the early infrastructure operation and maintenance technology and management concepts are relatively backward, resulting in the waste of resources and energy, and a large amount of greenhouse gases are generated.
2. Insufficient system planning of the "three ends" of urban underground infrastructure
At present, the carbon emission statistics of urban underground infrastructure have not been carried out, and the carbon emissions of underground infrastructure have not been mapped from the perspective of "three ends". Therefore, the carbon emissions of underground infrastructure in mainland cities have the problem of unclear bases, and it is impossible to optimize energy conservation and emission reduction in a targeted manner. Specifically, (1) at the source end, the current planning and design of urban underground infrastructure is still dominated by thermal power or other fossil fuels on the energy side, and clean energy accounts for a relatively small proportion, which is related to the energy structure of the mainland. (2) On the consumer side, the existing underground infrastructure equipment is outdated, the use of low-energy electrification equipment is less, and the intelligent operation management system has not been formed, resulting in large direct carbon emissions in the operation process. (3) At the carbon sequestration end, most of the existing carbon capture, storage and utilization (CCUS) technologies are still in the R&D demonstration stage, and have not yet reached the level of commercial promotion. Therefore, it is necessary to find out the amount of CO2 that needs to be fixed in urban underground infrastructure, and at the same time accelerate the construction of urban underground infrastructure application scenarios of carbon capture and storage (CCS)/CCUS technology.
3. Lack of measures to ensure the low-carbon development of urban underground infrastructure
At present, there are still problems in the early planning, policies and regulations, technical standards and other aspects of urban underground infrastructure, which are manifested in the complex functions of existing underground infrastructure, complex structure, scattered construction management and operation, lack of construction standards, and lagging urban infrastructure construction standards. In addition, the mainland has not yet established a perfect urban underground infrastructure carbon trading market system, and there is a lack of policy support and financial subsidies specifically for the low-carbon construction of urban underground infrastructure projects, and there are some difficulties in financing the construction of underground infrastructure.
4. The concept and strategy of low-carbon development of urban underground infrastructure
(1) The concept of low-carbon development of urban underground infrastructure
As a part of urban construction, urban underground infrastructure needs to follow the requirements of urban development and construction, fully implement the concept of green development, and actively explore the development concept of hierarchical development, classified development and intelligent development. (1) The concept of green development, through the rational use of underground space resources, energy and its own energy-saving advantages, to prevent environmental pollution and damage, improve the social environment of human settlements, coordinate the relationship between human beings and the natural environment, and build a green, low-carbon and circular urban underground infrastructure. (2) The concept of hierarchical development, scientifically and reasonably determine the hierarchical development mode of urban underground space, so that the development of underground space is carried out in accordance with the principles of orderly, rational and beneficial, and form a vertical hierarchical three-dimensional construction pattern of urban underground infrastructure, which is conducive to improving the energy conservation and emission reduction benefits of urban underground infrastructure. (3) The concept of classified development, according to the use function of urban underground infrastructure, scientifically build an efficient urban underground infrastructure system that coordinates different types of infrastructure such as transportation, pipe network, public service, logistics, etc., so as to improve the level of urban resilience and indirectly achieve energy conservation and emission reduction. (4) The concept of intelligent development, the use of modern information technology, the building information model (BIM) platform, geographic information system (GIS) technology and underground space planning combined, give three-dimensional, real performance of the underground foundation engineering model parameters, the establishment of urban underground infrastructure planning, construction and operation model, improve the rationality and efficiency of urban underground infrastructure planning, design, construction and operation.
(2) Low-carbon development strategies for urban underground infrastructure
Underground space is different from above-ground space, and its development and construction are irreversible, and must be planned before construction to maximize benefits. In the whole life cycle, the low-carbon development of urban underground infrastructure mainly includes the low-carbon construction of new infrastructure and the low-carbon transformation of existing infrastructure. Among them, the new urban underground infrastructure includes three stages: planning and design, construction and physical construction, and operation and maintenance, and the transformation of existing urban underground infrastructure mainly includes green transformation and green expansion.
1. Low-carbon development strategies for new urban underground infrastructure
In the planning and design stage, the urban underground infrastructure should be planned and designed according to the level. In terms of urban scale, combined with land and space planning, we should cooperate with the city to do a good job in top-level planning and design, coordinate the urban underground space, and determine the scale and function of underground infrastructure through the analysis of the overall development strategy of the city, so as to optimize the overall energy consumption structure of the city. In terms of the scale of aboveground and underground integration, the design principle of complementary functions of upper and lower functions is followed, and the long-term use function and spatial layout are considered, so as to give full play to the advantages of underground space, save energy consumption, and meet the needs of expanding the functions of original facilities in the process of urban renewal. In terms of the scale of underground infrastructure itself, by establishing a relationship between the building volume and function and carbon emissions, the carbon emission design process is adopted, and clean energy is adopted at the energy access end, such as ground source heat pumps, solar energy and wind power, etc., energy conservation and emission reduction facilities are mostly used at the energy consumption end, the underground greenhouse gas collection and recovery system is designed by using the closure of underground space to facilitate carbon sequestration, and the low-carbon planning and design of underground infrastructure is regulated and constrained by using the building carbon trading market.
In the stage of construction and physicization, the low-carbon construction strategy of urban underground infrastructure mainly includes three aspects: (1) strengthening the use of green building materials and energy storage building materials, giving full play to the performance of surrounding rock, reducing the amount of cement, or using new high-performance green building materials to reduce carbon emissions at the source of building material production and improve the durability of infrastructure. (2) Promote intelligent construction and industrial construction technology, apply information management platform, and adopt local prefabricated construction technology to reduce carbon emissions at the consumption end of the construction process. (3) Promote the research and development of carbon sequestration technologies for construction, such as the use of CO2 to consolidate the drainage of foundations, and realize the storage and reuse of CO2.
In the operation and maintenance stage, there are three main strategies for the operation and maintenance of urban underground infrastructure. (1) Intelligent operation strategy, using the characteristics of constant temperature and humidity, concealment and safety of underground space, the urban "intelligent brain" infrastructure is built underground, forming an urban intelligent operation and maintenance infrastructure system, optimizing the integrated operation efficiency of the ground and underground, and improving the overall energy conservation and emission reduction level of the city. (2) Electrification operation strategy, the operation of underground infrastructure is driven by green electricity, and a distributed energy storage system is established through energy piles, energy tunnels, underground electric garages, etc., to form an underground "virtual power plant" and coordinate the management of power supply for power market and grid operation. (3) The zero-carbon operation strategy uses the closed nature of underground space to build underground CCS/CCUS infrastructure, and uses deep storage technology and compressed gas energy storage technology to store greenhouse gases generated by the operation of urban underground infrastructure.
2. Low-carbon transformation strategies for existing urban underground infrastructure
Green transformation strategy. For the existing underground infrastructure with high energy consumption and high carbon emissions, green transformation is required, including electrification transformation, intelligent transformation and functional transformation. Electrification is to use electricity as an energy source to supply various equipment in underground infrastructure, so it is necessary to update all kinds of equipment to ensure the operation of infrastructure to low-energy, high-durability electrification equipment, and realize energy conservation and emission reduction of existing urban underground infrastructure by strengthening the operation efficiency of infrastructure. Intelligent transformation is the use of modern information technology and the concept of multiple functions, combined with the intelligent control function of electrified equipment, to automatically adjust the operation and shutdown of equipment according to the use of demand, to avoid waste of resources and energy. Functional transformation is to transform the existing idle urban underground infrastructure space, and at the same time use reinforcement technology to improve the durability of engineering facilities, on the one hand, strengthen the functional requirements of these engineering facilities in wartime or emergency, on the other hand, it can also realize idle utilization, and indirectly achieve energy conservation and emission reduction.
Green Expansion Strategy. In view of the problem that the scale of the original urban underground infrastructure cannot meet the current use needs, green expansion can be carried out. The expansion is similar to the strategy of the new urban underground infrastructure, first of all, the spatial planning and design of the expansion should not only respect the original underground infrastructure and not have a negative impact on it, but also match the original infrastructure, supplement its functions, and realize the intersection of the old and the new, and the harmony and difference. Secondly, it is necessary to ensure the structural reliability and functional reliability of the old and new connections, because the connection between the old and new spaces is the weak link of the overall structure, and it is necessary to optimize the mechanical performance of the connecting parts during the construction process to improve the durability of the overall structure, and at the same time, it is also necessary to coordinate the barrier-free connection of the use functions at the junction of the old and the new.
5. Low-carbon, energy-saving and emission-reduction technologies for urban underground infrastructure
In order to promote the low-carbon development of urban underground infrastructure and help achieve the "dual carbon" goal, the "three ends" of urban underground infrastructure should be taken as the starting point, and the integrated technology of distributed energy utilization \u2012 transmission \u2012 consumption \u2012 storage in urban underground infrastructure should be actively developed, as shown in Figure 1. At the source end, clean energy such as solar energy, wind energy, biogas energy, hydrogen energy and geothermal energy are used; on the consumer side, the underground power transmission and distribution system integrated with intelligent operation and maintenance is used to provide energy for the operation of underground infrastructure, and the underground distributed energy storage system is used to carry out peak regulation of electricity, optimize the efficiency of power transmission and consumption, and improve the energy conservation and emission reduction benefits of the consumer side; at the carbon sequestration end, underground CCS/CCUS is used for carbon sinks, such as foundation consolidated carbon sequestration, underground air compression infrastructure, etc.
Fig.1 Integrated technology of underground distributed energy utilization, transportation, consumption and storage
(1) Develop clean energy utilization and underground energy storage technologies at the source
Research and development of technologies for the efficient use of geothermal energy with the help of urban underground infrastructure. According to the geothermal energy at different depths, with the types of underground infrastructure at the corresponding depths, geothermal energy utilization technologies for different application scenarios are developed to avoid carbon emissions and energy consumption caused by deep distance transmission, and at the same time, open up the channels for the utilization of clean energy such as solar energy, wind energy, and biogas energy in the underground infrastructure, so as to form an urban underground infrastructure energy supply system dominated by geothermal energy and supplemented by other clean energy.
Give full play to the advantages of underground space and develop underground distributed energy storage technology. Underground compressed air energy storage, underground energy storage power stations, underground water source heat pumps \u2012 biogas cogeneration cycle energy storage, underground energy storage garages, hydrogen production energy storage by water electrolysis, etc., to form an underground distributed energy storage system and participate in power peak shaving. When there is a surplus of electricity, it is stored through a distributed energy storage system, and when the power is insufficient, it is supplied with power through an energy storage system, so as to achieve energy conservation and emission reduction at the source. Similar to distributed storage, distributed energy storage has the characteristics of decentralizing power resources, improving energy storage capacity, improving system reliability, availability and access efficiency, and distributed energy storage systems are also easy to expand. For example, the design method of Nanjing Children's Hospital's deep well parking lot adopts the combination of deep well parking lot and automatic charging piles for automobiles, which effectively solves the problems of parking, charging and energy storage.
(2) Develop intelligent operation and maintenance and industrial construction technologies on the consumer side
Intelligent O&M technology is the core breakthrough in the low-carbon development of urban underground infrastructure, and the optimization of O&M control links can not only reduce urban energy consumption, but also improve the utilization capacity of intermittent renewable energy and achieve energy conservation and green energy consumption. The core of intelligent operation and maintenance is how to integrate modern information technologies such as digital twins, artificial intelligence, big data, and numerical simulation into the decision-making and analysis of the whole life cycle of urban underground infrastructure, and form a carbon evaluation system for intelligent operation and maintenance of low-carbon cities. The key scientific problems of intelligent O&M technology include: (1) real-time and accurate acquisition of energy consumption and carbon emission data information of urban underground infrastructure, revealing the identification, classification, coding and transmission mechanism of all-factor data information, clarifying the mapping and interaction mechanism of multi-source and multi-dimensional information data, and realizing the mining and processing of information data under spatio-temporal changes. (2) Master the principle of intelligent control, establish a reasonable and effective intelligent human-machine cooperation model and coordination mechanism for energy conservation and emission reduction, and complete the construction of a refined management and optimization decision-making platform for urban load demand and energy consumption. (3) Open up the information and data transmission channels of new and old underground infrastructure, establish a carbon emission assessment model of existing underground infrastructure, realize its digital upgrade, and complete the low-carbon reinforcement and energy-saving transformation of urban underground infrastructure. For example, to update the lighting system of the early underground infrastructure, the semiconductor light-emitting diode (LED) light source can be used to replace the traditional lighting source, and the energy consumption can be saved by more than 50%; Remote control, timing, centralized and other control methods to achieve intelligent, energy-saving and environmentally friendly lighting. By replacing the lighting system as a whole and adopting an intelligent control system, lighting energy consumption can be reduced by more than 70%.
In the context of the vigorous promotion of building industrialization, according to the construction characteristics of underground engineering, the construction technology of local prefabricated underground structures can be developed. The side walls and bottom plates of the underground structure can be cast-in-place, and the rest of the components (such as the roof and the middle column, etc.) can be prefabricated and assembled. Compared with the cast-in-place method, the prefabricated building can reduce construction waste by 70%, save cement mortar by 55%, and reduce water consumption by 25%. At the same time, the use of BIM virtual construction technology can realize the refined management of local prefabricated projects. Compared with the fully assembled construction method, the partial assembly method can reduce the difficulty of construction and waterproofing, and improve the construction efficiency. In addition, the local assembly technology can improve the industrialization level of underground structure buildings, and at the same time, the arched prefabricated roof can be matched with flexible prefabricated nodes, which can greatly improve the seismic resistance of underground structures.
(3) Research and development of carbon capture and storage technologies for underground infrastructure at the carbon sequestration end
Due to the airtight nature of urban underground space, it is easier to capture CO2 than aboveground. Direct air capture (DAC) technology uses chemisorption materials and physisorption materials to capture CO2 emitted by distributed sources. Compared with above-ground space, underground space is more enclosed, with limited area for direct contact and circulation with air, and needs to be supplemented by ventilation equipment for indoor and outdoor air exchange. By adding carbon capture equipment to underground ventilation facilities, such as using carbon capture technologies such as liquid absorption, solid adsorption and membrane separation, the collection of greenhouse gases generated during the operation and maintenance of urban underground infrastructure is completed. Increase the research on the improvement of the adsorption effect of physical adsorbents at room temperature, carry out the development of high-efficiency and low-cost equipment, and solve the problems of good material adsorption effect but high cost, easy regeneration of adsorbent materials but poor adsorption effect. The development of ground-based carbon sequestration and sequestration technologies can effectively promote carbon capture and storage in underground infrastructure by using the carbon capture capacity of the soil itself.
6. Countermeasures and suggestions
(1) Mapping the greenhouse gas emissions of urban underground infrastructure
For urban underground infrastructure in different fields, coordinate the work of relevant departments, comprehensively carry out the census and statistics of urban underground infrastructure, find out the background of urban underground infrastructure, and establish urban underground infrastructure data centers; The building life cycle carbon footprint evaluation methods given in international standards and national standards consider the characteristics of underground infrastructure, unify the carbon emission intensity indicators and greenhouse gas accounting standards of urban underground infrastructure, and develop life cycle carbon footprint evaluation methods and analysis models. Based on the carbon footprint evaluation method and analysis model, the carbon emission data center of urban underground infrastructure was established from the perspective of "three-end" system planning or underground infrastructure category, and the carbon emission background of urban underground infrastructure was clarified.
(2) Improve the top-level design for low-carbon development of urban underground infrastructure
In the planning stage, according to the characteristics of different cities, the appropriate future development plan of underground infrastructure should be formulated, and it should be incorporated into the urban design and urban renewal plan. In the design stage, the connection between the new underground infrastructure and the surface facilities and the surrounding existing underground facilities should be strengthened, and the functional portability and development of the infrastructure itself should be considered to avoid waste of resources. In the construction stage, adhere to the principle of planning first, then construction, underground first, then aboveground, update the current underground infrastructure construction standards and specifications, encourage relevant departments, enterprises and other departments to participate in the preparation of technical standards, and carry out pilot work.
(3) Strengthen technology research and development for low-carbon development of urban underground infrastructure
At the source end, we will research and develop technologies for the efficient utilization of clean energy and distributed energy storage technologies for urban underground infrastructure, and continue to promote the proportion of clean energy electricity. Digital twins and other modern information technologies will build an intelligent management platform for underground infrastructure, improve energy efficiency, and promote low-carbon industrial construction technology for urban underground infrastructure.
(4) Strengthen the policy preference for low-carbon development of urban underground infrastructure
Formulate carbon trading policies for urban underground infrastructure, promote the establishment of carbon trading markets for urban underground infrastructure, and improve the market system. Establish a green energy consumption evaluation and certification system, improve the green energy consumption mechanism of underground infrastructure, and actively guide green energy consumption. Establish a reference basis for the evaluation of urban infrastructure underground transformation projects, and give relevant demonstration project policy preferences and financial subsidies.
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About the Author:
Du Xiuli
He is an expert in earthquake engineering and an academician of the Chinese Academy of Engineering.
He is mainly engaged in seismic research of large-scale engineering structures.
Note: The paper reflects the progress of research results and does not represent the views of Chinese Journal of Engineering Science.