# Suitability Evaluation of Urban Underground Space Development: A Case Study of Qingdao City
## 1 Introduction  
In the accelerating process of urbanization, evaluating the suitability of urban underground space development becomes increasingly critical. With the rapid increase in urban population, land resources are becoming increasingly scarce, and traditional urban development models struggle to meet demands, exacerbating urban issues [1]. Assessing the development potential of urban underground space not only maximizes the utilization of limited land resources but also alleviates surface congestion and resource scarcity, enhancing overall urban quality of life and environmental standards. Moreover, it contributes to promoting sustainable urban development by scientifically planning and utilizing underground space, improving resource efficiency, and reducing energy consumption and environmental pollution. Furthermore, evaluation results serve as vital references for urban planning, guiding the rational utilization of underground space and ensuring the city's long-term goals and sustainability. In summary, conducting evaluations of urban underground space development suitability is an indispensable measure for addressingurban land resource scarcity, mitigating urban issues, promoting sustainable development, and guiding urban planning [2]. Many scholars have evaluated the suitability of urban underground space development from various perspectives [3]. Some methods require the functions of the city's underground space, such as some underground structures, while others are mainly based on the engineering geological conditions of the underground and the urban planning demand conditions above ground. Currently, the majority of research on factors influencing the evaluation of urban underground space development suitability is divided into two main aspects: engineering geological conditions and urban planning requirements [4; 5; 6]. In terms of engineering geology, for example, in the underground space planning of the Minneapolis-Saint Paul area, [PERSON] et al. [7]. conducted a thorough examination of the influence of factors such as stratum distribution, hydrogeological conditions, and topography by conducting an overlay analysis of these factors to determine the distribution of suitability for underground space development within the study area. In the study of underground space land use planning in Finland, [PERSON] et al. [8] developed a model for assessing the suitability of underground space development, focusing on excavation challenges across various rock layers. [PERSON] et al. [9] utilized the transparent overlay method to examine the engineering geological conditions in the designated region, determining the distribution range and capacity of available underground space in the Quebec region of Canada and assessing its development difficulty. [PERSON] et al. [10] proposed a GIS-based 3D geological structure model, which has been applied in the planning and management of urban underground space development. [PERSON] et al. [11] have devised a model for evaluating geological suitability for urban underground space development, focusing on engineering geology and site stability among other aspects. This model has been applied to the urban underground space development planning in Changzhou, China. In addition to engineering geological conditions, urban planning factors also play a crucial role in decision-making regarding urban underground space development [12; 13; 14; 15]. [PERSON] [16] studied population density and urban underground space construction volume correlations in Stockholm, Paris, and Tokyo. The findings indicate that areas with higher population densities tend to have larger-scale urban underground space development. [PERSON] et al. [17; 18], examining Shanghai's districts and counties as case studies, explored the relationship between underground space development intensity and three urbanization indicators: per capita GDP, population density, and housing prices.