REMOTE SENSING ANALYSIS OF LAND SUBSIDENCE AND VEGETATION RESTORATION CHARACTERISTICS IN EXCAVATION AND FILLING AREAS OF MOUNTAIN REGION FOR URBAN EXTENSION IN YAN'AN

The excavation and filling works is frequently conducted in geotechnical engineering activities in collapsible loess area,which can easily lead to a series of geo-environmental problems such as land subsidence and vegetation damage. This paper examines the land subsidence and vegetation restoration characteristics of the mountain excavation and city construction project for Yan'an New District. Firstly,the basic characteristics of the project are obtained using visual interpretation and DEM extraction method from the remote sensing images. Then,the ground settlement of the study area is detected based on SBAS techniques. Finally,the NDVI time series data are extracted by GF-1 remote sensing images. The conclusions can be found as follows. (1)The urban construction projects of Yan'an New District are two years later after the large-scale land creation projects. The filling area is distributed along the valley of the original terrain. The maximum thickness of the excavation and filling square is more than 90m. (2)The main settlement area of Yan'an New District is the filling area. The maximum subsidence rate is 45mm ·a^-1 from 2017 to 2018. There is no obvious land subsidence in the excavation area where the main construction project is located. The man-made loess slopes are mostly in a stable state. (3)The average NDVI of Yan'an New District increases 230% from 2013 to 2015, and increases 50% from 2015 to 2018 with apparent vegetation restoration. The planning and construction of the mountain excavation and city construction project in Yan'an New District has reasonably avoided land subsidence and alleviated the deterioration of ecological environment. The results can provide scientific references for the similar projects.