苏锡常地区第四系沉积物结构变化特征与地面沉降生命周期过程研究

In this project, the land subsidence is considered as a life cycle process. From the structural characteristics of Quaternary deposits, including pore distribution, structural linking force and physic-chemical properties, the structural changes of the deposits at the different phases of land subsidence in Su-Xi-Chang area will be studied; the relationship between the land subsidence and ground water exploitation will be further analyzed; and the mechanism of later period of land subsidence in Su-Xi-Chang area will be revealed. The following achievements in the project are anticipated as: (1) the structural change law of Quaternary deposits will be grasped in the life cycle process of land subsidence in Su-Xi-Chang area; A structure-based evaluating method to determine the developing phases in the life cycle of land subsidence will be proposed; (2) the deformation mechanism of weak permeable strata will be revealed in the later period of land subsidence; (3) the relationships between the deposit deformation and ground water table changes and its exploitation will be analyzed at the different phases in the life cycle of land subsidence; (4) the final settlement of some typical land subsidence areas will be estimated. The research achievements of the project will be of great significance for understanding the life cycle process of land subsidence and proposing the scientific and rational countermeasures to control the later period of land subsidence in Su-Xi-Chang area.

本项目将地面沉降作为一个生命周期过程，从苏锡常第四系沉积物的结构孔隙特征、结构连接力以及物理化学水理性质变化，探究地面沉降生命周期过程不同阶段的沉积物结构特征，进一步揭示地下水开采量与地面沉降变形间的关系，弄清苏锡常地区后地面沉降阶段的沉降变形机理，以期取得以下成果：（1）获得苏锡常地面沉降生命周期过程中，第四系沉积物的结构变化规律，提出地面沉降生命周期过程阶段的结构评价和判定方法；（2）掌握后地面沉降阶段弱透水层变形的规律和机理；（3）掌握地面沉降生命周期过程中各个阶段的变形与地下水开采量和地下水位间的关系；（4）对苏锡常典型地面沉降区的最终沉降量进行估算和预测。研究成果对于掌握苏锡常第四系沉积物地面沉降全过程，对后地面沉降阶段提出更加科学合理的地面沉降综合治理措施，具有重要意义。

该项目经过四年的研究，按计划完成了项目书中的各项研究内容，获得了预期成果，达到了预期目标。（1）通过对苏锡常沉降区第四纪地层的系统研究，掌握了沉降区第四纪地层沉积物的物理力学性质；（2）对苏锡常沉降区第四纪地层沉积物的微观结构与土体粒度成分关系进行了定量分析，掌握了地面沉降生命过程中，第四纪沉积物的结构变化规律以及孔隙结构与固结变形间的关系；（3）采用光纤监测技术对钻孔全断面地层变形分布及承压含水层水位进行了长期监测，发现苏州地区现阶段主要含水层的压缩量已不明显，主要压缩层为与抽水含水层相邻的两个隔水层释水压缩所致；（4）开展了排灌水土体变形响应模型及排水时弱透水层变形模型试验研究，发现弱透水层压缩曲线具有明显的分段特征，变形与含水率具有良好的对应关系。当土中含水率低于液限时，弱透水层压缩速率明显加快；回灌时当含水率高于液限后，回弹速率明显加快；（5）提出了地面沉降生命过程阶段性评价理论判据。在苏锡常地区地面沉降分布式光纤长期监测的基础上，提出了孔隙比率指标法（Ecl和Esa）作为理论判据，可简单快速评价土层的压缩潜力，划分出地面沉降生命过程的阶段性，该判据的提出对地面沉降的防治具有重要意义。