| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1987: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 1986: ¥1,200,000 (Direct Cost: ¥1,200,000)
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| Research Abstract |
1. The bearing capacity of pipe piles is statically indeterminate on account of increasing in diameter. The force per unit area shows a tendancy to vary as the ratio of thicknes to diameter as the load is made larger and the mechanism, which transfers end resistance to the upper part of piles between the extent which is twice as long as diameter at the tip ,is formed, but it may vary as the diameter as long as the load is small.
2. The behaviours of open or closed pile were simulated by the F.E.M analysis, and then it is presumed that the ground will be settled by the pile mainly under the cone formed by the principal stress direction due to the ultimate state of friction near the pile top.
(1) The inner soil settles with the pile so that the inner friction is negligible except the pile tip At the pile tip, however, outer or inner friction is larger than other part owing to arching of sand particles.
(2) In the case of the open pile, sand near the tip did not fail but near the top failed.
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(3) In the case of the closed pile, in which the rigid stratum at 5m under the tip which plugged by the concrete between the extent which is twice as long as pile diameter, the friction reached the ultimate value in order from the rip to the upper part and the sand near the tip was failed.
(4) From the above mentioned ultimate state of friction and the failure of sand, the usual yielding load and 'the first ultimate load', named by Kishida and Takano, were observed in order.
3. For improvement of friction element and unloading element of sand after failure in the method, the displacement control or flexibility method must be introduced. The stres values of sand near the tip reach the particle crushing range so that the constitutive law must be improved also. Errors of circumferential strain near the axis of symmetry or the precise definition of stress and strain must be investigated.
4. For the above mentioned improvement, triaxial test method with end frictionless pieces was established and the test will be conducted by strain control. Less
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