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The evaluation of urban underground space (UUS) suitability involves multiple indicators. Assigning weight to these indicators is crucial for accurate assessment. This paper presents a method for spatially variable weight assignment of indicators using the order relation analysis method (G1-method), the entropy weight method, an improved grey relational analysis (GRA) and a set of spatial weight adjustment coefficients. First, the subjective and objective weights of indicators for engineering geological and hydrogeological conditions were determined by the G1-method and entropy weight method, respectively, and their combined weights were then obtained using the principle of minimum discriminatory information. This study highlighted the impact of surface restrictions, such as buildings, on UUS, and the degree of the influence of these buildings gradually decreased with the increase in depth of the rock and soil mass in UUS, which resulted in changes in weights of indicators with depth. To address this issue, a coefficient was defined as the standardized value of the ratio of additional stress applied by restrictions to the self-weight stress of soil at the same depth to modify the combined weights so that all weights of indicators could vary in space. Finally, an improved GRA was used to determine the suitability level of each evaluation cell using the maximum correlation criterion. This method was applied to the 3D suitability evaluation of UUS in Sanlong Bay, Foshan City, Guangdong Province, China, including 16 evaluation indexes. This study comprehensively considered the influence of multiple factors, thereby providing reference for evaluating the suitability of UUS in big cities.

Abstract Traditional methods for understanding geological conditions, such as borehole drilling and on-site tests, are often costly and impractical for extensive urban areas like Wuhan’s Main Urban Area. This study introduces an innovative geological–geotechnical zoning framework that utilizes limited data to overcome these challenges, essential for urban planning, underground space development, and construction design. We began by dividing the study area into four primary geological units based on geomorphological characteristics, using a novel method validated at four metro stations. Our approach incorporated data from 1544 geological boreholes to compile a comprehensive database, from which six typical stratigraphic profiles for each unit were identified. These profiles facilitated the estimation of potential layers and their corresponding geotechnical parameters, and the identification of subsurface hazards. The study resulted in a detailed engineering geological zoning divided into nine secondary units. Our analysis not only demonstrates the effectiveness of the proposed criteria for geomorphological units in achieving more accurate and quantifiable outcomes but also shows the framework’s suitability for regions with complex sedimentary conditions. The resultant engineering geological zoning enhances understanding of geological risks, providing a foundation for safer and more sustainable urban development.

Abstract The utilization and development of urban underground space play a crucial role in optimizing the layout of civic architecture and enhancing the urban ecological environment, which contributes toward increasing the overall carrying capacity and promoting sustainable development in megacities. To delve into the research progress of urban underground space, knowledge maps were created using the information visualization software VOSviewer. The literature was systematically extracted from three prominent databases, namely, Web of Science, Scopus, and China National Knowledge Infrastructure. According to the bibliometric analysis of the co‐citation and core words co‐occurrence, the trends and challenges of research on urban underground space were identified. As highlighted by the results obtained, it still remains highly challenging to achieve interdisciplinary collaboration in urban underground space research; the research trends of urban underground space consist of collaborative planning and whole life cycle sustainable development, multisource geological data informatization and resource evaluation, infrastructure design optimization, and intelligent construction. The knowledge map, drawn using bibliometric methods, offers a quantitative analysis of literature retrieval across various levels. It is recognized as an essential tool for exploring and identifying challenges and trends in urban underground space.

As a crucial component of urban development and territorial space resources, the urban underground space plays an increasingly important role in the new development stage. This study analyzes the new demand and challenges in the new development stage and proposes development strategies of the urban underground space accordingly. Based on the characteristics and requirements of the new development stage, this study analyzes the strategic demand for urban underground space utilization from the perspectives of territorial space planning system, green and low-carbon resilience concepts, and urban renewal modes. Subsequently, it proposes a series of new challenges to be addressed for urban underground space development in the new development stage. These challenges include the deficiency in territorial resource investigation and assessment, ambiguity in underground bearing capacity, deficiency in exploiting the low-carbon and resilient potentials of the urban underground space, and imbalance in resource allocation and ambiguity in development mechanism of the infrastructure. Furthermore, eight priority tasks and corresponding development suggestions are proposed from the aspects of legal and administrative system development, smart management of resources, planning theories and methods, data-driven paradigm, deep space utilization, spatial reconfiguration of built space, integral development of new areas, and regulation of metro-led space. This study is expected to provide insights for the legislation, planning, construction, and management of the urban underground space.

The development of urban underground space (UUS) is of great significance for sustainable urban development because it has potential to solve many urban problems. However, the development of UUS is limited because there are still a lot of constraints and challenges. To better understand the constraining factors of developing UUS and improve the development and utilization of UUS, this study conducts a comprehensive survey of existing literature retrieved from the Web of Science Core Collection database. Five main constraining factors, including the limited geological conditions, high cost, lack of natural light and ventilation, high incidence, and difficulty in collecting data and information on UUS, have been discussed to better understand how they affect the development of UUS. Based on the survey, the critical success factors of developing UUS, such as the effective governance structure, planning system for integrating UUS into urban development, coordination of the design of ground and underground, delineation of land property rights of UUS, and application of information techniques in the use of UUS, have been identified and discussed. In addition, knowledge gaps in the studies on development of UUS have been identified. Finally, the research trends and future directions have been proposed for better understanding and practice of UUS development.

The evaluation of geological suitability for urban underground space (UUS) development is an indispensable prerequisite for its optimal utilization. As the actual carrier of underground facilities, the evaluation of rock mass quality plays a crucial role in assessing geological suitability. However, it is notable that the evaluation of rock mass quality has regrettably remained somewhat marginalized within the broader framework of the geological suitability assessment in recent years. The selection of pertinent indicators for the evaluation of rock mass quality inherently presents an appreciable degree of subjectivity. Predominantly subjective evaluation methods continue to dominate the field, while the application of objective algorithms, such as unsupervised clustering, remains in its nascent stage. Furthermore, there is a lack of comprehensive investigations into distinct combinations of attributes. This limitation confines the broader applicability of the evaluation outcomes in the context of urban underground space. Within this study, we meticulously amassed rock core test data from over 40 boreholes of engineering geological significance within the urban planning ambit of Guang'An City. Utilizing the K-means unsupervised clustering algorithm and the Principal Component Analysis (PCA) algorithm. We successfully conducted an unsupervised clustering procedure with nine distinct physical and mechanical attributes. This yielded an aggregation into five discernible clusters. Building upon the derived clustering outcomes, a stratification of rock mass quality was effectuated into three distinct tiers: Level 1 (characterized by pure sandstone), Level 2 (primarily dominated by sandstone), and Level 3 (denoting fair conditions predominantly influenced by mudstone). This structured stratification facilitates a relatively objective and comprehensive evaluation of rock mass quality within the context of the red-bed hilly terrain. In the course of this analytical trajectory, we conducted a dissection of the clustering efficacy. For strongly correlated attributes, we propose a preliminary dimensionality reduction procedure prior to the clustering endeavor. Moreover, we recommend intervals of 10 m for the stratified evaluation in red bed hilly urban terrains.

Abstract The development of urban underground space is a critical way to alleviate the lack of urban resources, and improve environmental conditions as well as residents' quality of life, which has important practical significance. As the most densely populated and economically developed areas, coastal cities face many challenges in underground space development owing to their unique environmental geological conditions. This study examined the current situation of underground space development, academic research, technology application, evaluation methods, planning, and legislation in coastal cities in China. On this basis, it analyzed the future development trends, and presented reasonable suggestions for the critical scientific and technical problems faced by the development of underground space in coastal cities. The key suggestions are as follows: it is necessary to define and clarify the critical geological issues, distributions, and hazards that affect underground space development and major engineering construction in coastal cities; the land‐sea integrated detection technology for sea crossing bridges and submarine tunnels needs to be studied; in evaluating the suitability of underground space in coastal cities, the land and sea area evaluation factors should be integrated; and the evaluation system of land‐sea integration needs to be established.

Urban underground space, as an underutilized land resource, holds tremendous potential and value. Efficient and rational development and utilization of this resource are key to addressing current urban challenges. This study takes the main urban area of Qingdao City as an example and establishes a comprehensive evaluation system for the suitability of urban underground space development at different depth levels through the integration of geological, hydrological, and urban planning factors. By utilizing the Analytic Hierarchy Process to assign weights to evaluation criteria within the system, both a multi-objective linear weighting function model and a fuzzy comprehensive evaluation model are employed to assess the suitability of underground space development. The results delineate the distribution of underground space development suitability within the study area. Comparative analysis of the two models reveals that the fuzzy comprehensive evaluation model offers a more detailed and comprehensive reflection of the complexity and diversity of underground space development, providing forward-looking and insightful evaluation results for urban planning and development. The evaluation indicates that certain streets within the main urban area of Qingdao exhibit excellent prospects for underground space development.

The concept of disaster prevention and mitigation is vital for the safe development of urban underground space. Considering the coexistence of natural and engineering safety risks, the concept needs to be improved for further development of the urban underground space, and it is imperative to follow a disaster-adaptation-oriented concept that emphasizes post-disaster recovery resilience of the urban underground space. This study analyzes the implications and influencing factors of recovery resilience and summarizes the research on recovery resilience from the engineering and non-engineering perspectives. Moreover, the development status of recovery resilience research is analyzed from the aspects of structural system, evaluation method, management mechanism, space planning, and emergency plan. On this basis, a strategy that consists of three stages and an evaluation system is proposed; it categorizes post-disaster recovery into three stages—emergency rescue, recovery, and plan adaptation—and proposes recovery goals for each stage, providing a basis for the establishment of a recovery resilience evaluation system for the urban underground space.Furthermore, we suggest that the management regulations and emergency plans of the urban underground space should be optimized, the resilience planning improved, and intelligent management promoted, thereby realizing the orderliness and high efficiency of urban underground space recovery.

The contradiction between urban construction and sustainable development has led to an increasing demand for urban underground space (UUS). The value evaluation of urban underground space (UUSVE) is of great significance in promoting the rational development of UUS. Currently, no study has reviewed the literature on UUSVE. This paper provides a preliminary review of the legal basis and element composition of UUS, and the themes, evaluation objects, and evaluation methods of UUSVE, attempting to clarify the current status of UUSVE and analyze its future development trends. Finally, by summarizing the legal basis, element composition, research status and trends of UUSVE, three suggestions to strengthen UUSVE are proposed: (1) to strengthen the research on the shortcomings of UUSVE methods; (2) to build an evaluation index library and case library; and (3) to emphasize interdisciplinary collaboration, with a particular focus on the application research of machine learning.

Abstract:Subway stations are one of the most popular public spaces in the Iranian big cities, which is accompanied by urban design low qualities. The urban design of knowledge, art, and profession is the organization of the environmental qualities of the urban and public domain of the subject. Considering low qualities in these modern spaces that are used by everyday people, the most important issue of the present research is constructed without reference to indigenous fields. Emphasis on indigenous patterns, in the construction of underground spaces, especially subway stations, can lead to the sustainability and desirability of these spaces. The development of urban-rural spaces can play an important role in the sustainability of contemporary large and populated cities. Construction and construction of these spaces is a new phenomenon in Iran that can weaken or strengthen the natural, human, social, cultural, and economic characteristics of cities such as Tehran. In this paper, the purpose of this paper is to explain the status of the design of urban design in metro station spaces, with emphasis on indigenous patterns. The present study is conducted using the descriptive-analytical methodology and studies between the three areas of urban design and related qualities; subsurface development and metro station spaces; native architectural and urban design patterns. Therefore, after the design of the problem and terminology, the study of definitions and urban design qualities from the point of view of the experts and the addition and extraction of comprehensive urban design qualities was done with the article approach. Subsequently, in order to study Imam Khomeini, Seventh, and Revolution Square subway stations, they were studied and analyzed. The results of the study indicate that the planning and design of metro station spaces should pay attention to the comprehensive design quality of the city. These qualities include identity recognition, environmental sustainability, socioeconomic and economic sustainability, safety and security, efficiency and diversity, accessibility and accessibility, continuity and integrity, proportions and human scale, freedom, flexibility, Vitality, intuition and sensual richness, justice. The analysis of case examples, both in terms of both generic and indigenous patterns, has a low status and poor quality of urban design and indigenous patterns. In general, paying attention to the design qualities of a design based on native patterns can enhance their sustainability, utility, and humanity.IntroductionUrban design is a science, art, and profession dealing with organizing the environmental qualities of urban and public areas. Paying attention to the vacuum of urban design qualities in these modern spaces that are used daily by people is the most important issue of the present study, which has been constructed without any connection with local contexts. By presenting this issue, the purpose of this study is to explain the position of urban design qualities in metro station spaces with an emphasis on local patterns. In the process of urban development, all aspects of environmental quality must be considered. In other words, strengthening or meeting one or more (private and public) needs and environmental quality should not lead to the weakening or loss of other environmental qualities. This is an issue common in contemporary projects. One-dimensional views of urban projects, such as a purely economic or traffic approach, will neglect the underlying features, undermine identity, and move in the opposite direction of sustainable development. The theme of this research is that, on the one hand, the development of urban infrastructures such as metro stations, especially in large cities and their centers, is a matter of certainty and these infrastructures in the dimensions of transportation, space, play an important role in the life of urban centers. But on the other hand, the construction of these spaces is often devoid of environmental qualities and less attention is paid to local patterns. The research hypothesis is that by accompanying and using local models in the planning and development of subsurface spaces, both goals can be achieved, namely the development of urban infrastructure, strengthening urban identity, and improving environmental qualities. Therefore, this study seeks solutions to use local patterns in the development of subsurface spaces and subway stations. Research Methods This study aims to analyze the position of urban design qualities in the design of metro stations. The study is conducted using a combined research approach (i.e. quantitative and qualitative methods). In this regard, the most important research question is: What is the position of urban design qualities in the design of metro stations? Also, the research sub-questions are: What are the qualities of urban design effective in the design of metro stations? What are the ways to apply these qualities with emphasis on indigenous patterns in subway stations? In this research, while analyzing the features and qualities of native patterns, the application of these patterns, related features, and qualities in the planning and design of contemporary underground spaces in our country are discussed and solutions and suggestions are presented. Therefore, while defining these concepts from the theorists’ point of view, we summarize and conclude these definitions, and then search for native patterns of architecture and urban planning for use in the planning and design of metro stations. Research Findings The results of the study show that in planning and designing metro station spaces, comprehensive qualities of urban design should be considered. These qualities include identity, legibility, environmental sustainability, social, cultural and economic sustainability, safety and security, efficiency and diversity, pedestrianism and ease of access, cohesion and integration, human proportions and scale, freedom, flexibility, vitality, attractiveness and sensory richness, and justice. The analysis of case studies, both in terms of general qualities and indigenous patterns, indicates the low and weak position of urban design qualities and indigenous patterns. In general, paying attention to urban-design qualities with a focus on indigenous patterns can promote their sustainability, desirability, and humanity. Emphasis on indigenous patterns in the construction of underground spaces, especially subway stations, can lead to the stability and desirability of these spaces. The development of suburban urban spaces can play an important role in the sustainability of large and densely populated contemporary cities. The construction of these spaces is a new phenomenon in Iran that can weaken or strengthen the natural, human, social, cultural, and economic characteristics of cities like Tehran.From all these issues, it can be concluded that the role of subsurface spaces, including metro stations, in the sustainable development of cities, should be taken seriously and the comprehensive realization of environmental qualities should be considered by avoiding one-dimensional approaches in planning and designing these spaces. It can also be said that traditional Iranian indigenous buildings and collections such as Gudal Baghcheh, Shovadan, Cistern, the historical bazaar have valuable structural features (in terms of the form and function on architectural and urban scales) and can be a local model for the development of metro station spaces. Given that our country is on the verge of developing such spaces, paying attention to these points can play an important role in stabilizing cities and strengthening urban identity, and improving environmental qualities. These templates and design guides can be used in the planning and design of metro station complexes. Since the metro network is one of the most widely used underground spaces in large cities, the subsurface development in relation to metro stations and using the native patterns studied in this research can be useful and effective. Keywords: Urban Design Qualities, Metro Stations, Urban Underground Space, Indigenous Patterns, Tehran Metro. References- Alexander, C., & Chermayev, S. (1992). The book areas of collective and private life. Translated by Manouchehr Mozyani. Tehran: Tehran University Press.- Appleyard, D., & Jacobs, A. (1987). Toward an urban design manifesto. Journal of the American Planning Association, 53(1), 112-120.- . (2007). Charter of new urbanism. 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The growth simulation of urban underground space (UUS) under the consideration of ecological constraints can effectively reveal the characteristics and trends of UUS changes, and provide a basis for planning the construction of sustainable and livable ecological cities. Therefore, this study considers urban ecological space as a constraint mechanism for UUS development and conducts a simulation study of the dynamic and complex UUS growth process, with a view toward guiding UUS planning under a long-term overall vision. In this study, a patch-based cellular automaton (CA) model is constructed to simulate the dynamic and complex growth process of UUS, subject to the ecological constraints generated by the agent-based land allocation optimization model. The spatial drivers of UUS growth simulation are determined based on the Random Forest (RF) algorithm. The results of the research case in Tianfu New District, Chengdu City, demonstrate that UUS expansion with ecological constraints exhibits sustainable characteristics. However, the growth rate of the UUS development scale is significantly lower when ecological constraints are present compared to when they are not. This study’s results contribute to urban management by finding a balance between UUS development and ecological space conservation, and providing theoretical support for rational UUS planning and decision making in the construction of low-carbon cities.

Urban geological modeling (UGM) is a fundamental approach for the visualization of underground space and recognition of complex geological conditions of a city. Previous UGM studies, with the assumption of homogeneous geological characteristics, have resulted in deviated modeling properties due to the negligence of parameters with obviously different spatial distributions in lithologies. This study presents a case study of Guang’an city in SW China by using a sequential simulation interpolation (SSI) method that reflects geological heterogeneity by combining field surveys, topography, borehole data, geological profiles, and stratigraphic columns to establish a lithology distribution model in the study area. The geotechnical attribute model of the area of interest was established based on lithology to capture subtle variations in lithology due to obvious differences in geotechnical characteristics of clay, sand, mudstone, sandy mudstone, and shaly sandstone. This 3D model could provide a reference for the urban underground space master planning and future sustainable development of Guang’an city. In addition, this study also discusses the prospects and directions of urban geological modeling and provides a few suggestions for engineering in urban areas.

Three-dimensional (3D) geological models are currently needed and used independently for urban development. The main difficulty in constructing a 3D geological model of a shallow subsurface is to determine the stratigraphic distribution. Highly variable properties and geometries of geological units beneath lead to difficulty. It is key to find a practicable and efficient way to construct a model in practical work. This study takes Tongzhou District (Beijing) as a case; 476 boreholes (40 newly drilled and 436 existing engineering boreholes) were utilized combined with the cross-section method to construct an integrated 3D geological model. The framework and analyses contributed to the following applications: (1) High-quality information from new boreholes and existing engineering boreholes were used to define stratigraphy and build cross-sections. (2) The resulting geological model (up to 50 m beneath Tongzhou area) shows many details of the shallow subsurface. This includes 10 major layers which were grouped into three cyclothems representing cyclic sequences of clay, interbedded silt, sand, and gravel with variable quantities of lenses. (3) The new model was used as a tool to visualize the depth and geometry variations below ground and to characterize a large variety of properties (for example, the compression modulus analyzed in this paper) that each unit contains, and then to evaluate the underground geological conditions. (4) An analysis of a dynamic monitoring model based on the resulting 3D model indicated that the geological units (sand and silty clay) at depths between 30 m and 40 m, with an average vertical deformation of 0.97 mm, from July 2019 to September 2020, are suitable for underground construction, from the perspective of vertical stability in the study area. Monitoring models that take time into consideration based on a 3D framework will be further explored.

The development of underground space resources can alleviate the problems of traffic congestion and land resource tension caused by urbanization, but there are also certain risks in the development of underground space, so the suitability of development needs to be evaluated. This paper takes the geological suitability of underground space resources in Weihai City as the evaluation object, establishes the index system for evaluating the geological suitability of underground space resources development and utilization, determines the criteria for quantifying each factor index, uses the hierarchical analysis method to determine the index weights and applies the fuzzy C-mean clustering algorithm to evaluate the geological suitability of underground space resources development and utilization in the urban area of Weihai City, and achieves excellent results that are more in line with the geological conditions.

Fire-protective super thermal insulator is an inorganic material with a nanopore structure and super-low thermal conductivity. It can be classified as either a sol-gel aerogel-based composite or a fumed oxide-based composite. The matrix oxides are investigated from SiO2 to oxides with higher melting temperatures, including Al2O3 or ZrO2. It was found that the complex component oxides with the appropriate ratios exhibit better thermal stability than single oxide when exposed to fire. The infrared opacifier is a key component to this material that can significantly reduce its high-temperature thermal conductivity. The appropriate selection of opacifiers becomes possible by determining the specific infrared extinction coefficient and performing a numerical calculation based on Mie scattering theory. This fire protection material has high fireproof efficiency while also being very thin and is rated as having high fire resistance. With the development of ambient pressure drying for aerogel-based composite from supercritical drying, this fire protection material can be manufactured at low overall cost and will play an important role in passive fire protection systems in urban underground spaces.

Interest in underground space development is increasing owing to overcrowding in urban areas, and this trend is expected to continue in the future. Therefore, there exists a need to systematically establish and manage information on underground spaces. This information includes both the physical status, that indicates the location or shape of the space, and the status of property rights related to the ownership and use of the space. In this study, a technique to register an entire underground shopping center space including individual store spaces along with the relationship with the above-ground parcels is proposed. The study considers the current management and operation system of the underground shopping center. 3D data were acquired from the Gwangbok Underground Shopping Center in Busan Metropolitan City, Korea using terrestrial LiDAR equipment. The VWorld data of the Korean Ministry of Land, Infrastructure, and Transport were also used as pre-built data. Furthermore, a spatial information-based management system was implemented. The data used comprise registration information for establishing property rights. These have the physical status and rights status information of the ground parcels as attribute information.

The dialectic between vertical and horizontal urban development models seems to leave out the depth of the underground. The increasing urbanization, the consequent strong density as well as growing environmental concerns push the search for new models of development towards the subsoil frontier. Recognized resilience properties and a strong potential for sustainability indicate the underground as a natural destination for strategic infrastructures, consolidating its reputation as a surface service layer. Instead, we want to illustrate how the underground can contribute incisively to the revision of urban models by introducing new spatial and performance parameters, both in new and historic contexts, and how it is now urgent to achieve integrated planning and planning of the environment in all its depth.

Shanghai is being transformed through a process of rapid urbanization. Urbanization has the effects of increasing urban population and the income levels of residents as well as changing the structure of transportation. Under the background, from the 1980s, Shanghai has increasingly built and extended underground pedestrian systems (UPS) within central areas to complement pedestrian networks. UPS have significantly affected urban life in Shanghai under the decades of development but to date, research on UPS usage and perceptions of UPS users has been lacking. This research conducted an on-the-spot survey in Shanghai's UPS in People's Square, Jing'an Temple and Xujiahui areas. Investigation through observation, face to face questionnaires and interviews generated qualitative and quantitative findings on the usage characteristics and perceptions of UPS users. The discussion focused on social usage and equity and the functionality of UPS. It revealed defects in the design and management of Shanghai's UPS, including deficiencies with regard to consideration of the elderly, disabled groups, management of homeless people, the range of merchandise categories and orientation (i.e. way-finding) systems. This research is a significant contribution to enriching knowledge and providing insights into the performance of UPS in a developing country under rapid urbanization.