地面沉降的三维离散元模型建立和模拟研究

On the basis of the characteristic that soils are loose debris in micro scale, discrete element models for sand particles and clay particles will be built in the project, with which a three-dimensional discrete element model can be established for the simulation of land subsidence. A software "MatDEM" will be developed to run specific three-dimensional discrete element simulation. According to the analysis of composition and gradation of soils, corresponding discrete element models will be built to simulate the processes of soil compression and subsidence, which can be compared with the characteristics of soil compression and variation of micro structures during soil experiments. Both three-dimensional numerical simulations and experiments of soil ground water extraction and reinjection processes will be established, to reveal the irreversible changes of soil structures and the macro response during water extraction and reinjection processes. The project provides a new research method for the study of land subsidence.

本项目从土体结构系统为松散堆积物这一特点出发，建立具有一定力学性质砂颗粒、粘土颗粒的离散元模型，并构建用于模拟地面沉降过程的三维离散元模型；自主研发软件"MatDEM"以进行特定的三维离散元模拟；根据土体的成分和级配，建立相应离散元模型并模拟土体压缩沉降过程，与实验中土体的压缩沉降特性及其微观结构变化进行对比分析；开展土体地下水抽取和回灌过程的模型箱试验和三维离散元模拟，揭示土体结构系统在地下水抽取和回灌过程中的不可逆变化及宏观变形响应，为地面沉降的研究提供一种新的研究方法。

地面沉降及其诱发灾害已成为影响我国区域经济可持续发展的重要因素之一。本项目围绕地面沉降的三维离散元模型建立和模拟研究这一中心课题，针对地面沉降砂粘土层离散元建模，砂粘土层压缩特性和离散元模型，以及抽灌水过程中土层变形规律这三个方面的科学问题，开展了系统研究。在本研究中，(1)提出了土体三维紧密堆积离散元模型微宏观力学关系，以及能量转化原则；研发了岩土体大型三维离散元软件MatDEM，并建立了砂土和粘土的离散元模型；(2)改进传统的固结仪，实现了砂土压缩过程中微观结构提取和量化，掌握了砂的级配和形态等参数对其压缩性和蠕变性质的影响，并建立三轴试验和固结试验离散元模拟器，开展数值模拟测试和试验对比分析；(3)通过结合野外监测、室内抽灌水模型箱试验和离散元模拟，揭示了抽水过程中粘土层负孔隙水压力对其压缩沉降的重要作用，提出了苏锡常地区地层在抽灌水循环中持续沉降的机制。项目达到了预期目标，研究成果对于认识地面沉降过程具有重要的理论和现实意义。