## 4 Results
### Comparative Analysis of the Suitability of UUS Development Under Different Constraints  
Due to significant variations in engineering geological conditions, development levels, and ecological conservation constraints among different regions, comparing the suitability evaluation results under different constraints can better assess the potential and risks of underground space development in various areas, providing guidance for regional development planning. Based on this premise, this study evaluated the zoning of underground space development suitability in Nantong City under the same geological conditions but without considering regional development levels and ecological conservation area constraints. The evaluation results are depicted in Figure 20, and a comparison of suitability evaluation results is presented in Table 5, with and without considering regional development levels and ecological conservation area constraints. When considering the constraints of regional development levels and ecological conservation areas on underground space de  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Suitability Level** & **Distribution** & **Characteristics** & **Development Proposals** \\ \hline \multirow{5}{*}{Suitable} & The total area is about 1179 km\({}^{2}\), accounting for 14.74\% of the city’s land area. It is mainly distributed in Rugao City, Chongchuan District, and the southwest of Rudong County. & The geological and hydrogeological conditions in the region are good, with no risk of geological hazards; the economic level is developed, the surface land resources are more valuable, with high potential value and demand for development, and thence is no distribution of ecological protection zones. & The construction difficulty is low, the foundation treatment methods are simple, and no special reinforcement or anticorrosion layer treatment is needed. The development cost is low, and it is suitable for the construction of underground pipeline corridors, underground commercial streets, and other underground projects. & The geologic environment is good, but the presence of special soils, such as soft soils and silty clays, as well as groundwater constraints, require appropriate foundation treatment methods and reinforcement measures. The potential risk of geologic hazards should be noted during development. Development costs may be higher compared to suitable areas, but it can still be developed. & The geologic environment is good, but  
velopment, the proportion of suitable development areas decreased by 6.29%. Meanwhile, the areas classified as more suitable, generally suitable, and unsuitable for development increased, indicating that underground space development is significantly influenced by regional development levels and ecological conservation areas. Furthermore, a comparison between Figures 19 and 20 reveals that certain areas in the western and northwestern parts of Haian City, as well as the northeastern part of Qidong City, are classified as unsuitable for development due to their relatively lower economic levels, low population density, and location within ecological conservation areas. Additionally, areas in Liuqiao Town, Shigang Town, and Sian Town of Tongzhou District are surrounded by the Tonglv Canal ecological corridor, leading to a decrease in development suitability when considering ecological conservation area constraints. Moreover, the southern coastal areas of Haimen District, characterized by high economic development, population density, and road density, exhibit a strong demand for underground space and the potential for higher economic benefits from development, resulting in an increased level of development suitability.