Subsidence monitoring and influencing factor analysis of mountain excavation and valley infilling on the Chinese Loess Plateau: A case study of Yan'an New District

With the significant expansion of the urban population on the Chinese Loess Plateau, large-scale land infilling and excavation projects have been implemented to alleviate the shortage of construction land. However, loess collapsibility associated with engineering disturbances can often lead to geological hazards, such as land subsidence. The Yan'an New District (YND) is the largest area of mountain excavation and valley infilling on the Loess Plateau. Post-construction subsidence is likely to threaten future infrastructure; therefore, the monitoring and analysis of the settlement are essential. The temporal and spatial distribution of settlement in the YND was investigated, and the key influencing factors, such as filling, construction, and precipitation, were analysed in this study. Integrated with remote sensing methods, such as SBAS-InSAR technology, shadow altimetry, and uncrewed aerial photogrammetry, were used, which have seldom been applied to regional analysis. The results revealed that the rate of deformation in the YND from 2015 to 2019 was-73 to 18 mm/yr, and in the fill area, the maximum cumulative subsidence was 256 mm, while in the excavation area, the maximum cumulative uplift was 35 mm. We obtained a linear regression model for the fill area, which indicated that settlement was positively correlated with the fill thickness and negatively correlated with the building height. In the excavation area, there was no clear relationship between the excavation thickness or building height on deformation. In the fill area, no obvious collapsible settlement was observed during the rainy season, and uplift occurred in the excavation area, with a maximum uplift of 17 mm.