Abstract: In order to unify the standards of the underground stratification system, this paper collected the related data of underground stratification requirements for major domestic and international cities, and analyzed the main natural and social factors for the urban underground space development. The main natural factors are terrain, geomorphology and engineering geology distribution, which determine difficulties and costs of underground space development. The main social factors are city scales, location conditions, and local policies and regulations, which determine demands for underground space. The results show that regional demands and difficulties in development determine the development scales, which in turn affect the underground stratification. In most cities, the underground space is divided into shallow, sub-shallow and deep layers that are separated at 15 m and 30 m depths, respectively. The shallow underground space is greatly influenced by topography and geomorphology and should be stratified in the sub-shallow region. The underground space should be layered along the normal of the ground surface in the steep slope area. Based on them, this paper established a hierarchical evaluation index system for underground space, which provided a certain guidance and reference significance for urban underground space planning.

Key words: underground space, stratification of underground space, underground development, city planning