| Budget Amount *help |
¥4,000,000 (Direct Cost: ¥4,000,000)
Fiscal Year 2004: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 2003: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 2002: ¥2,100,000 (Direct Cost: ¥2,100,000)
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| Research Abstract |
The mechanism of the liquefaction in saturated sand and soil resistance during an earthquake has been gradually made clear since 1964 when the Niigata earthquake occurred. In recent years, however, the damages due to the liquefaction caused by the large earthquakes have been reported, for example the Hokkaido-nansei-oki earthquake in 1993, the Hyogoken-nambu earthquake in 1995, the Tottori-seibu earthquake in 2000, and so on. In the Hyogoken-nambu earthquake, the large-scale liquefaction occurred in the wide area from the former coastline to the reclaimed land, and the damages occurred in the pile foundation under buildings. The cause of damages of the pile foundations has investigated by some researchers. However, many uncertainties to establish the design method for laterally loaded piles supporting a building still remain, especially when considering effective stress reduction in soil around piles due to pore water pressure increasing during an earthquake. Therefore, we devised and
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made the appropriate test apparatus for decreasing effective stress in the test sand bed by using the seepage flow, and performed laterally loading tests in order to investigate the subgrade reaction acting on the model pile.
The following points are found out from these studies :
1.The lateral subgrade reaction on the pile at a given level is approximated by the hyperbola with respect to the lateral displacement of the pile. Then the initial modulus and the convergence of the hyperbola are related to the initial coefficient of the lateral subgrade reaction and the ultimate lateral subgrade reaction, respectively.
2.Both of the initial coefficient of lateral subgrade reaction and the ultimate value increase linearly with depth (i.e. triangle distribution), and decrease linearly with decreasing the effective stress in the sand bed. From these results, we are able to present the new design method of pile foundations on the basis of the subgread reaction analysis which considers the reduction of effective stress in ground during an earthquake.
3.Furthermore, the analysis for the pile group foundation based on the three dimensional theory, which considers an elasto-plastic continuum and the ultimate lateral resistance of the soil around the piles, is also proposed. Less
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