A study of the characteristics of land subsidence and the main control factors in the alluvial plain: A case study of Beijing plain

The long-term excessive exploitation of groundwater in Beijing has triggered a series of geological environment problems, especially the land subsidence. In this paper, the authors reviewed the development history of the land subsidence in Beijing, and analyzed the characteristics of land subsidence in both the horizontal and the vertical aspects. On such a basis, the main control factors of land subsidence in Beijing plain were investigated. Some conclusions have been reached:(1) The land subsidence is divided into two zones and seven settlement centers. The northern part of the subsidence area is composed of many settlement centers, and the extension of the southern part northward is obvious. (2) In the southern part of the subsidence area, the first compression layer is the main contribution layer, which accounts for 42%. The sedimentation rate of the shallow layer is decreased and the deep layer is increased. The deformation characteristics of soil are plastic deformation and creep deformation. In the northern part of the subsidence area, the second compression layer is the main contribution layer, which accounts for 65%. The sedimentation rate of the shallow layer is small and that of the deep layer is relatively large. The deformation characteristics of shallow soil are mainly based on elastic deformation, and the deep part is plastic deformation, which contains the creep deformation. (3) The land subsidence is controlled by structure, and the expansion range of northeast area is limited. The land subsidence area is expanded in northwest and southeast direction. (4) Stratigraphic structure determines the distribution of land subsidence. The difference between the north pluvial facies and the south lake deposition is the important factor responsible for different contribution rates of land subsidence. (5) Exploitation of groundwater is still the main factor which leads to land subsidence. The groundwater funnel area and the center of the land subsidence are highly consistent with each other. The falling rate of groundwater is proportional to the rate of land subsidence.