复杂含水层系统中地下水位变化驱动下的土层变形特征及其机制

The plain area of Beijing-Tianjin-Hebei has the greatest area of severe land subsidence, accounting for more than 80% of the total area of severe subsidence in China, so the situation of prevention and control of land subsidence is severe. Due to the limitation of the complex influencing factors and large variation in time and space of aquifer systems, the research on groundwater-derived deformation law of soil layers is weak so far, which restricts the scientific evaluation of the development trend for land subsidence and its forecast and early warning. Based on the monitoring data at typical borehole extensometers distributed in the monitoring network of Tianjin and Cangzhou, we propose to study the interaction mechanism between groundwater dynamics and the deformation of soil layers, and then classify and simulate this mechanism. Combined with soil tests of mechanical properties under loading and unloading conditions, creep tests and so on, we will conduct comprehensive analysis of the constructed soil deformation models and then obtain universal visco-elasto-plastic constitutive relations. In this work, effective methods will be explored to calibrate the hydraulic parameters using both groundwater level and subsidence data achieved from InSAR, GPS, geodetic leveling, etc. Eventually, case studies of forecast and early warning for land subsidence will be conducted by establishing 3D varying-coefficient soil-water coupling models of typical study areas. This project has great scientific value and significance to optimize the monitoring network of land subsidence, analyze quantitatively the monitoring data and improve the accuracy of land subsidence simulation, forecast and early warning, and will provide technical support to effectively relieve the disasters of ground subsidence caused by groundwater exploitation.

京津冀地面沉降严重区面积超过全国的80%，防治形势严峻。受含水层系统影响因素复杂与时空变化大等制约，迄今对地下水位变化驱动下的土层变形规律研究比较薄弱，限制了对地面沉降发展趋势的科学研判和预测预警。本项目拟从天津和沧州地区地面沉降监测网中遴选典型分层标组，研究地下水动力与土层变形互馈机制并进行归类、建模；在此基础上，结合加卸荷力学特性试验、蠕变试验等土工实验，对土层变形模型进行联合分析与综合，得到普适性强的土层粘弹塑性本构关系。探索联合利用InSAR、GPS、水准等多手段获得的地面沉降数据和地下水监测数据校正模型水文地质参数的有效方法，建立典型区三维变参数土-水耦合模型并进行地面沉降预测预警案例研究。本项目的完成，对京津冀地面沉降监测网的优化、监测数据的定量化分析、地面沉降模型仿真性和预测预警准确性的提高等方面具有科学意义，为有效缓解地下水利用引起的地面沉降灾害提供技术支撑。

京津冀平原地面沉降广泛分布，多发生在承压含水层发育的中东部平原。本项目以廊坊-天津-北京、沧州沉降区为重点，通过研究地下水水头与土层变形的关系揭示复杂含水层系统中地下水位驱动下的土层变形机制，为平原区地面沉降的形成、演化规律以及地面沉降预测预警提供了新的理论和方法。主要研究内容及结果如下：. （1）综合分析沧州沉降区地面沉降量时空变化数据，建立了沧州市区沉降中心地下水与地面沉降互馈关系模型，识别了不同地下水位变化模式下土层变形特征。根据高压固结试验数据，识别了地层主固结和次固结阶段的土层变形规律，提出了地面沉降临界水位计算的新方法。. （2）综合分析廊坊-天津-北京沉降区钻孔土样的高压固结试验数据，建立了深层黏性土压缩指数与其他物理指标的定量关系模型，求取了深层黏性土的压缩模量估算公式，提出了适用于研究区不同深度黏性土固结计算的本构模型；蠕变试验结果表明砂土变形具有蠕变特征；受试验过程无侧限影响，原位应力相对于常规条件，黏性土的固结变形更大。. （3）山前至滨海平原水-土耦合模拟表明，受地层与岩性差异影响，地面沉降由山前平原到滨海平原逐渐加重；考虑断裂、抽水影响的水-土耦合模拟得出，地面沉降、地表裂缝扩展过程与抽水位置、水位降深密切相关; 廊坊沉降区三维水-土耦合数值模型结果表明，联合开采深、浅含水层组有利于遏制地面沉降发展。