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

在高地下水位土的开挖中，管涌、沸腾等渗流破坏是开挖基础的一个问题。即使在技术进步的最近几天，渗漏破坏也会发生。因为原地条件通常是三维的，所以渗流破坏问题应该用三维来处理。渗流问题应从一维流动、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角度来讨论。本文将轴对称渗流作为三维渗流模型来讨论土体的渗透破坏问题，从理论上将柱状破坏的概念推广到轴对称渗流条件下。讨论了二维流、二维流和轴流条件下的渗流形态和临界水头差Hc。3-…的效果明确了等势线上渗流的更多维集中、临界水头差H_c、破坏模式等，并在AXSflow条件下进行了25例渗流破坏试验。考虑了等势线的变化、土体形态随水力压差H的增大而变化。阐明了H-Q&lt；15&gt；关系、变形时的水头差、破坏时的水头差，为完善渗透破坏理论提供了依据。通过实例研究，了解土体渗流情况，明确破坏原因，找出防止渗流破坏的方法是非常重要的。本文讨论了三个实例：(1)第一新川大桥桥墩底土开挖中的沸腾问题；(2)沉箱桩施工(K线桥台施工)过程中土体颗粒喷出问题；(3)三野井筒内开挖土体渗透破坏的稳定性问题。案例研究对于理论应用于实践以及理论研究和实验研究都具有重要意义。在此基础上，提出了全面建立渗流破坏理论的必要性。较少

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