非稳态管涌侵蚀下土体变形过程与渐进失稳机理

Accidents are prone to happen in engineering under rainfall and flood conditions, and because of the seepage force, fine particles are brought out so that soil’s deformation increases or its strength decreases, which lead to unsteady of soil. In practical engineering, the water levels which soil bears change with time and the occurrence of piping is also hidden, so it is difficult to predict the additional soil’s deformation and changes of strength characteristics induced by erosion. This research is only about cohesiveless soil. First of all, based on the theory that the soil is comprised by skeleton particles and movable particles, deduct the equation of particles motion and find out the laws of the migration of particle swarms under unsteady water levels. Second, the unsteady water levels of practical engineering are simulated when doing piping tests, and the samples are also under the certain stress conditions when doing tests. After piping tests, the laws of soil particles loss under different head level functions can be unveiled, which can be used to establish multiple critical development model of piping under unsteady water levels. Third, according to the triaxial compression test of piping soil, to find out the relationship between mechanical properties of piping soil and the mass of fine particles loss of piping soil. Finally, combining the relationship between functions of unsteady water levels and fine particles loss with the relationship between fine particles loss and mechanical properties of piping soil, a theory about the development of piping and the progressive failure mechanism of piping soil can be established, which will be used to analyze and control the stability of soil under seepage in practical engineering.

工程在降雨、洪水情况下容易出现事故，一个重要的原因是渗流力作用下，土中发生管涌，细颗粒被带出，土体变形增加或强度降低，导致失稳。实际工程中，土受到的水头作用并非稳定不变，且管涌发生具有隐蔽性，土体被潜蚀诱发的附加变形与强度特性改变很难预测。研究以无粘性土为对象，首先区分土体骨架颗粒间隙与可动颗粒，考虑变动水头条件，推求颗粒运动方程与颗粒群运移规律；然后，针对处于一定应力环境下的土体，模拟实际工程中的变化水头，进行管涌试验，根据不同水头函数下土体颗粒流失规律，建立非稳定水头作用下的管涌多重临界发展模型；利用经历不同管涌过程的土体进行应力应变试验，获取颗粒流失量与土体进一步变形的关系以及土体的强度变化；最后，对应已知初始基本物理性质的土体，通过水头变化函数与颗粒流失的时间规律、颗粒损失与形变发展土体失稳这两种关系的结合，得到管涌发展与土体渐进失稳机理，用于工程中有渗流的土体稳定分析。

管涌侵蚀是水利工程安全的重要威胁，目前对于非稳定流水力作用下的管涌机理以及管涌侵蚀后的力学性质研究还较少。本项目通过自主研发的循环水力梯度作用下的内部侵蚀三轴仪，开展试验研究。研究分析了变动水头对间断级配砂土管涌的激化作用，引入了涌砂量扩大系数概念，定量得分析其与正弦水头形式之间的函数关系；同时，对于在超临界循环水力梯度作用下的整个管涌侵蚀发展过程的时间效应进行了详细研究；同样，通过添加黏粒发现其对砾类土渗透变形有一定得促进作用；在整个管涌发展过程中，细颗粒的流失量在整个土体空间的分布也呈现不同的规律，细颗粒的流失百分比与土层分布呈现正相关，并且正弦式非稳定水头对于试样结构影响较大。在管涌后的力学性质研究中，以颗粒流失量作为定量参数，研究了不同颗粒流失量下的土体峰值强度和变形特征得弱化规律，建立了考虑细颗粒含量影响下的修正摩尔-库伦准则和修正邓肯张模型。同时，对模型参数进行敏感性分析，讨论得出修正的模型参数波动对模型结果的影响程度。最后利用数值软件正弦周期水头作用下管涌后土进行大坝抗滑移安全系数和最大水平位移进行数值模拟，揭示其对岩土工程稳定性的影响程度。通过项目执行，完成了既定任务的规律总结，建立了相关模型，参加国内外学术交流10多次，项目负责人参与学术交流5次，做会议学术报告4次，特邀报告1次；邀请了2人次相关境外专家到河海大学进行学术交流；完成项目年度报告3份，结题研究报告1份，行业工程研究报告10余份；发表相关论文15篇；获得科技奖励4项，培养年青科技工作者2名，硕博士10余名。成果应用到了土木水利等多个工程，解决了上海青草沙水库大堤的渗漏导致沉降开裂问题、上海苏州河入海水闸渗漏沉降开裂等在内的20余个土木水利工程相关问题，成果被新疆水利部门、黄河水利委员会、淮河水利委员会等多家单位认可，产生了巨大的社会经济效益。