考虑砂土层内细颗粒流失作用的地面沉降机理与预测模型研究

Recently land subsidence of Shanghai and the region of Yangtze River Delta area presents new phenomenon that the deformation of aquifer presents continuous increase whereas the deformation lagged the recovery of groundwater level. The existing theory of land susidence prediction cannot reasonably interpret this phenomena. This research proposal investigates the mechanism and prediction model of land subsidence via consideration of internal erosion of fine silty and clay particles in the pore of aquifer sand strata in Shanghai, which is natural sedimentary sand layer with clay lenses. Laboratory test, soil erosion coupled theory, and numerical simulation will be employed to solve following scientific problems: i) to reveal the condition result in internal erosion of fine particles in aquifer sand and the erosion patterns, and to investigate the relationship between erosion of fine particles and hydraulic gradient, seepage velocity, distribution of clay lense, and grading of soils; ii) to reveal the deformation behavior of aquifer sand after erosion of fine particles, and to establish the quantitative relation between the content of fine particles and deformation of aquifer sand. iii) to establishe the prediction model of land subsience to consider the dynamic process with the erosion of fine particles in aquifer sand strata. This study is benefit to strengthen prediction and to control land subsidence in the regions with multi-aquifer-aquitard-system, and to reallocate well of groundwater withdrawal-recharge rationally and to control the injection pressure during recharge of water.

近年来上海及长三角地区的地面沉降出现了含水层砂土持续变形增大与滞后的新特征。现有的地面沉降理论无法对此作出合理的解释与预测。本项目以上海地区含有黏土透镜体（千层饼）的砂土地层为研究对象，拟探明地下水采灌过程中砂土层内细颗粒流失作用引起地面沉降的机理并建立相应的地面沉降预测理论，通过室内试验、渗流侵蚀耦合理论、数值模拟相结合的方法，解决如下关键科学问题：①揭示含水层砂土中以"千层饼"形式存在的细颗粒产生流失的条件与变化规律，确定细颗粒流失与水力梯度、渗流速度、千层饼分布、颗粒级配等的关系；②探讨含水层中细颗粒流失后的砂土层受力变形性状的变化规律，建立细颗粒含量与砂土变形性状的定量关系；③建立可以考虑含水层砂土中细颗粒流失作用的地面沉降计算模型。研究成果可以突破传统地面沉降预测模型中仅考虑土层压缩系数的瓶颈，为多层含水层地区减少地面沉降、保护环境，确定有效地下水采灌格局提供科学依据与理论支撑。

本项目以上海地区的含有黏土透镜体的砂土地层为研究对象，通过室内试验、渗流侵蚀耦合理论、数值模拟相结合的方法，探明了地下水采灌过程中砂土层内细颗粒流失作用引起地面沉降的机理，解决了如下关键科学问题：①通过理论分析揭示了地下水开采引起的渗透压密机理及细颗粒流失的临界条件；②通过室内试验确定了含水层砂土中细颗粒流失的规律及影响因素，揭示了含水层中细颗粒流失后的砂土力学性状的变化规律；③建立了可以考虑含水层砂土中细颗粒流失作用的地面沉降模型。研究成果丰富了地面沉降的机理研究，对于提高多层含水层地区的地面沉降预测和防治设计水平，具有重要的理论指导意义。本项目共发表论文12篇，其中SCI期刊论文8篇；公开专利2项；培养研究生毕业2人。