冲洪积平原地面沉降特征及主控因素——以北京平原为例

北京由于长期过量开采地下水,相继引发了一系列地质环境问题,其中地面沉降问题尤为突出。回顾了北京地面沉降发展历史,从平面和垂向上分析了地面沉降特征,在此基础上对北京冲洪积平原区沉降的主控因素进行了研究。结果表明:(1)平面上,沉降分为南、北2个大区,7个沉降中心。北区已由多个单独沉降中心区扩展成一个大区域,南区北扩明显;(2)垂向上,南区第一压缩层为沉降主贡献层,沉降占比42%,浅部地层沉降速率减小,深部地层沉降速率增加。土体变形特征为塑性变形,包含蠕变变形;北区第二压缩层为沉降主贡献层,沉降占比65%,浅部沉降量值很小且波动平缓,深部沉降量相对较大。土体变形特征为浅部以弹性变形为主,深部以塑性变形为主,包含蠕变变形;(3)沉降受构造作用及基底格架控制,北东方向受冲洪积扇上部单一砂卵砾石的地层条件控制扩展范围有限,沉降整体向北西、南东方向扩张;(4)地层结构决定沉降平面和垂向分布特征,尤其北部冲洪积与南部湖相沉积的差异,是产生深浅部地层沉降贡献率不同的重要因素;(5)地下水开采仍是沉降产生的主因,地下水漏斗的扩展和沉降中心的分布高度吻合,主要沉降层地下水位下降速率与沉降速率成正比。

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.