|Budget Amount *help
¥7,000,000 (Direct Cost : ¥7,000,000)
Fiscal Year 1997 : ¥400,000 (Direct Cost : ¥400,000)
Fiscal Year 1996 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1995 : ¥6,100,000 (Direct Cost : ¥6,100,000)
Seepage failure is a problem in hydraulic structures, cofferdams at the location of high ground water level. Once the seepage failure occurs, it causes serious damage to the work itself and/or neibouring places from the economical point of view. There are still many problems unknown, in the seepage failure phenomena, which have to be made clear.
In this study, the seepage failure problem of soil within a cofferdam was mainly considered. First the existant theries of seepage failure given by Harza and Terzaghi are investigated precisely, and Prismatic failure -A new method of calculating stability against boiling of sand within a cofferdam is presented. Typical three examples (isotropic and antisotropic one-layred soils, and two-layred soil) were analyzed using these theories, and the characteristics of these theories of seepage failure were then clarified precisely.
Second eight examples of case histories on seepage failure were reported and analytical considerations of these problems we
re given. The possible causes of seepage failures for these examples were discussed and classified as follows : (1) Desige was mistaken or wrong countermeasures were taken. (2) Unexpected situation occurred. (3) Creep length was too short. (4) Inhomogeneous subsoil (including multi-layred soil) was encountered. (5) Seepage flow concentrated three dimensionally into the soil surrounded by a cofferdam. (6) Permeability of soil was highly anisotropic. (7) Rock foundation was weathering in deep excavation. (8) Seepage flow concentrated into the end of a structure constructed within a cofferdam during dewatering. (9) Filter was clogging with the passage of time.
Finally, 47 cases of experiments were made on seepage failure of soil within a cofferdam. Analysing the state of soil (homogeneity, anisotropy of soil), changes in formation of soil surface and distribution of equipotentials, the relationship between hydrautic head difference and discharge, hydraulic head differences at which soil starts being deformed and failure occurrs, and angle of repose of soil in water. The hydraulic head difference at which the soil starts being deformed is estimated from Prismatic failure (Friction). Relative density of soil makes effects on modes of failure, hydraulic head differences at being deformed and at failure.
大型二次元浸透破壊実験装置を用いて、琵琶湖砂2について、矢板の長さ、根入れ深さ、相対密度を変えたE0001〜E0047の実験を行った。まず、全ての実験に関して地盤の浸透流特性(均質性や異方性)を明らかにした:(1)地盤の均質性、(2)地盤の異方性、(3)水頭差の増加に伴う地盤形状の変化、等ポテンシャル線分布の変化、(4)変形時水頭差、破壊時水頭差、(5)水中安息角。そして、実験結果が矢板の根入れ比と限界水頭差の無次元量を用いて無次元化できること、変形時水頭差が著者らの提案したPrismatic failureの考え方を用いて説明できることを示した。また、地盤の相対密度と浸透破壊特性について考察し、相対密度が破壊形態、変形時水頭差、破壊時水頭差に及ぼす影響について明らかにした。 Less