|Budget Amount *help
¥8,200,000 (Direct Cost: ¥8,200,000)
Fiscal Year 2005: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 2004: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 2003: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 2002: ¥6,100,000 (Direct Cost: ¥6,100,000)
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-
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