THE ANALYSIS OF THREE-DIMENSIONAL (3D) GROUND SURFACE DEFORMATIONS IN HEIFANGTAI PLATFORM

The loess has strong collapsibility in Heifangtai Platform, Yongjing Country, Gansu Province which belongs to a typical loess platform. Collapsible loess of thick layer caused by long-term flood irrigation has induced many loess landslides and severe ground deformations. We selected ground deformations in Heifangtai Platform as research object. The descending data of Sentinel-1 A satellite in three different orbits were processed using PS-InSAR technique between 2014 and 2017, and the deformation in different line of sight(LOS) is obtained. In addition, 3 D ground surface deformations was obtained by inversion and calculation in the area. Ground surface deformations of LOS direction, vertical and horizontal direction was analyzed, and the development trend of ground surface deformation was predicted. The results show there are differential settlements in study area. The deformation rates of LOS direction are larger in some area including closing to central area of platform and the part of area on the edge of platform. The range of settlement is 4~13 mm·a^-1. A region with large vertical deformation is near the middle of platform. The average rate of deformation is-20~-6 mm·a^-1. The North-South deformations are small. The average rate of deformation is-5~5 mm·a^-1. However, the West-East deformations are large. The average rate of deformation is mostly more than 20 mm·a^-1. Ground surface deformations are still at a slow acceleration stage in short term as a whole. With continuous development of agricultural irrigation, the rate of ground surface deformation will gradually decrease after rising a certain value.