Theoretical and experimental study on seepage failure mechanism of soil in three-dimensions

在地下水位较高的土层开挖中，基坑底部的管涌、翻浆等渗透破坏是一个难题。即使在技术进步的最近几天，渗透破坏也会发生。由于原位条件通常是三维的，因此渗透破坏问题应按三维来处理。渗流问题应从一维流、二维流（2Dflow）、二维集中流（2DCflow）、轴对称集中流（AXSflow）、二维径向流和轴对称径向流等流动条件的观点来讨论。本文以AXSflow为三维渗流模型，讨论了土的渗透破坏问题，从理论上将棱柱体破坏的概念推广到轴对称渗流条件。讨论了二维流、二维直流流和AXSflow条件下的渗流流型和临界水头差H_c。三种影响- ...更多信息 阐明了渗流在等位线上的空间集中度、临界水头差H_c、破坏模式等，并在AXSflow条件下进行了25例渗透破坏试验。考虑了等势线随水头差H增大而变化、土的振型随水头差H增大而变化的情况。阐明了H-Q关系、变形水头差、破坏水头差等问题，指出了进一步完善渗透破坏理论的必要性。<15>通过实例分析，对了解土体渗流情况，弄清破坏原因，找出防止渗透破坏的方法具有重要意义。本文讨论了以下三个案例：（1）第一新川大桥桥墩地基开挖中的沸腾案例;（2）沉箱式桩施工（K线桥台施工）过程中的土粒涌出案例;（3）Misono竖井开挖土的渗透破坏稳定性案例。案例研究对于理论与实践的结合以及理论与实验研究都具有重要意义。根据本文的研究结果，有必要建立一套完整的渗流破坏理论。少

In excavation of soil with a high groundwater level, seepage failure such as piping, boiling etc. is a problem at the base of excavation. Seepage failure occurs even in recent days when technology has proceeded. Because an in situ condition is usually three dimensional, the seepage failure problem should be treated three dimensionally. Seepage flow problems should be discussed from a view point of flow conditions such as one-dimensional flow, two-dimensional flow (2Dflow), two-dimensional concentrated flow (2DCflow), axisymmetric concentrated flow (AXSflow), two-dimensional radial flow and axisymmetric radial flow. In this study, the seepage failure of soil was discussed for the AXSflow as a model of three dimensional flow.From a theoretical point of view, the prismatic failure concept was extended for an axisymmetric seepage flow condition. Seepage flow patterns and critical hydraulic head differences H_c were discussed for 2Dflow, 2DCflow and AXSflow conditions. The effects of three- … More dimensional concentration of seepage flow on equi-potential lines, critical hydraulic head differences H_c, modes of failure etc. were clarified.Seepage failure tests were conducted for 25 cases in the AXSflow condition. Changes of Equi-potential lines, changes of modes of soil with increase in a hydraulic head difference H were considered. H- Q_<15> relationships, hydraulic head differences at deformation, hydraulic head differences at failure were also clarified.Case studies are necessary for improvement of the theory of seepage failure. From case studies, it is important to understand the situation of seepage flow through soil, clarify the causes of failure and find out preventive methods against seepage failure. The following three case studies were here discussed : (1) A case study on boiling in excavation of subsoil for Daiichi-Shinkawa bridge pier, (2) Blow-out of soil particles during construction of a caisson type pile (K-line bridge abutments construction), (3) Stability for seepage failure of excavated soil within Misono Shaft.A lot of problems have remained in the present theory of seepage failure. The case studies are important for application of the theory to practice as well as the theoretical and experimental studies. Based on the results obtained here, it is necessary to establish the theory of seepage failure comprehensively. Less