Based on the vertical load test on an indoor sand half-surface model pile，the VIC-3D non-contact full-field strain measurement system was used to record the dynamic development of the soil displacement field around the expanded body in real time. By using digital image correlation techniques，the entire process of the soil displacement field distribution characteristics and development under the load was observed. The failure state of soil around the expansion body was investigated. The influence of different expanded diameters on the bearing capacity， the distribution of displacement，the compression zone and the subsidence zone was explored. The main compression area and main subsidence area were quantitatively analyzed. The results show that with the increasing diameter of the expanded body，the bearing capacity of the drilled-expanded concrete pile gradually increases，and the loaddisplacement curve of single pile changes from steep drop type to slow change type. The vertical and horizontal dis? placements of soil around the expanded body increase with the increase of pile top displacement，but the increased amplitude is affected by the buried depth，the distance from the expanding body and the distance from the boundary of the compression zone. The horizontal displacement of soil at different buried depths shows a "C" shape. The influ? ence range of soil displacement around piles increases with the increasing diameter of the expanding body，and the subsidence zone and compression zone are formed above and below the expanding body，respectively. The area of the regions is positively correlated with the diameter of the expanding body and the displacement of the pile top. Through nonlinear surface fitting，the functional relationship between the area of main compression area，main subsidence area，the diameter of expansion body，and displacement of pile top is obtained，which can provide some reference for the prediction of the area of main compression area and main subsidence area.