# Experimental Study on Cavity Formation and Ground Subsidence Behavior Based on Ground Conditions
## 7 Conclusions  
In this study, a laboratory model test was conducted to simulate the occurrence of ground subsidence using Korean standard sand and marine clay. The main objective was to identify the ground subsidence mechanism in urban areas. Ground subsidence tendencies were examined with respect to the relative density and groundwater level using standard sand. In addition, marine clay was mixed with the standard sand to quantitatively analyze the ground subsidence tendency with respect to the fines content. Figure 9: Conceptual diagram of cavity formation location with respect to the groundwater level (10, 20, 30 cm). The analysis of the ground subsidence mechanism with respect to the relative density revealed that cavity formation and ground subsidence accelerated with decreasing relative density. In the model ground, however, cavities and ground subsidence occurred regardless of the relative density, and the cavity volume increased with increasing relative density. This appears to have been due to the differences in the rate of soil loss caused by friction resistance between soil particles resulting from the relative density. Cavity formation and ground subsidence accelerated with increasing groundwater level. This appears to have been due to the occurrence of cavities near the groundwater level, and these were closer to the ground surface at higher groundwater levels, resulting in ground subsidence within a short duration. The fines content in marine clay was found to affect ground subsidence. As the fines content increased, a tendency was observed for cavity formation and ground subsidence to be increasingly suppressed. This was likely because the fines in the ground prevented the loss of soil particles as they moved to the damaged area at the bottom of the soil box under restrained conditions. In underground conditions with a fines content of less than 10%, the cavity volume increased with decreasing groundwater level. This also appears to be related to the cavity formation location with respect to the groundwater level. Structural stability can be ensured if the cavity formed is farther from the ground surface. In such a scenario, a large-scale cavity and considerable time are required for the collapse of the ground surface. Thus, the ground subsidence mechanism with respect to the relative density, groundwater level, and fines content was analyzed. A laboratory model test on ground subsidence was conducted by simulating the ground under various conditions in a soil box. However, loads (e.g., road and structural loads) on the ground surface similar to actual conditions were not considered. This may be a limitation in practically reflecting the ground subsidence mechanism. Moreover, considerable cost and time are required to simulate the model ground. This caused difficulty in repeating the tests, making it somewhat difficult to ensure reliability. This study confirms that effective groundwater level management is necessary for the prevention of ground subsidence accidents and that regular inspection of underground utilities is required to suppress the formation of cavities within the ground. In addition, the mechanisms of ground subsidence under various ground conditions presented in this study are expected to serve as fundamental reference data for the selection of backfill materials and construction methods during the installation of underground utilities. Conceptualization, S.L., J.K. ([PERSON]) and J.K. ([PERSON]); investigation, S.L. ; writing--original draft preparation, S.L. and M.K. ; writing--review and editing, S.L. and W.B. All authors have read and agreed to the published version of the manuscript. Research for this paper was carried out under the Korea Institute of Civil Engineering and Building Technology (KICT) Research Program (project no. 20250285-001 Development of infrastructure disaster prevention technology based on satellites SAR) funded by the Ministry of Science and ICT. Not applicable.