GroMoPo Metadata for Shanghai subsidence model

Shanghai city has been suffering land subsidence caused by overly exploitation of ground water since 1921, which is a serious problem for this coastal city with altitude of 2.2-4.8m above mean sea level. The largest cumulative land subsidence amounted to 2.6m in the downtown area. Measures to decrease the ground water exploitation, change the pumping aquifers, and increase aquifer artificial recharge have been used to mitigate land subsidence since 1961. It is necessary to develop a proper numerical model to simulate and predict land subsidence. In this study, a decoupled three-dimensional (3-D) finite element land subsidence model including a 3-D ground water flow model and a 3-D geo-mechanical model was developed to simulate the 3-D deformation of the aquifer systems in the center area of Shanghai. The area of downtown Shanghai is 660 km(2), with 10 million inhabitants, dense high buildings, and 11 metro lines. The simulation spans the period from 1979 to 1995. Two different assumptions have been tested on the side boundary, i.e., precluding the three components of the displacement, or assuming a free-displacement condition. The distribution of calculated land subsidence and horizontal displacements in different aquifers was analyzed. The computed vertical displacement fitted well with the available observations. It has been verified that the two different assumptions on the lateral boundaries in the geo-mechanical model caused different results just limited on nodes close to boundary. The developed 3-D land subsidence model is reasonable and can be used to simulate and predict 3-D movement of aquifer systems in the center area of Shanghai, which could provide scientific support to local government in controlling land subsidence and differential movements of the land surface.

自1921年起，上海市便因地下水过度开采遭遇地面沉降问题。作为一座海拔介于平均海平面2.2至4.8米的滨海城市，地面沉降已成为其面临的严峻挑战。市中心区域的累计最大地面沉降量达2.6米。自1961年起，当地已通过减少地下水开采、更换开采含水层、增加含水层人工补给等措施，以缓解地面沉降态势。因此，开发适配的数值模型以模拟并预测地面沉降十分必要。本研究构建了一套解耦式三维（3-D）有限元地面沉降模型，该模型由三维地下水流模型与三维地质力学模型组成，用于模拟上海市中心城区含水层系统的三维变形。上海市中心城区总面积达660平方千米，常住人口约1000万，高层建筑密集，且运营有11条地铁线路。本次模拟的时段为1979年至1995年。针对模型侧边界，我们测试了两种不同的边界假设：一是限制位移的三个分量，二是采用自由位移条件。研究分析了不同含水层中计算得到的地面沉降与水平位移分布特征，计算得到的垂直位移与实测观测数据拟合度良好。研究证实，地质力学模型中侧边界的两种不同假设，仅对边界附近节点的计算结果存在影响。所构建的三维地面沉降模型具备合理性，可用于模拟并预测上海市中心城区含水层系统的三维运动，可为当地政府管控地面沉降与地表差异沉降提供科学支撑。