The problem that occurs during open-ended steel pipe pile installation is that soil enters the pipe and develops frictional resistance that further prevents soil intrusion, causing plugging and increased piling resistance. The steel pipe pile with tapered tip (tapered tip pile) restrains plugging and piling resistance. To apply the tapered tip pile as end-supported piles, it is essential to clarify the bearing capacity mechanism suitable for tapered shapes. In addition, it is not possible to apply the bearing capacity mechanism of the flat tip pile (straight pile). The purpose of this paper is to reveal the piling performance and the bearing capacity by experiment and to propose the bearing capacity model based on the mechanism in a fully plugged mode. Experiments were conducted on model-tapered pipe piles installed in sands with different soil conditions to investigate the effects of the pile shape on piling performance and bearing capacity. Extending the combination theory of Prandtl and cavity expansion, bearing capacity model and formula incorporating shape parameters were derived. Theoretical values were good agreement with the experimental results.
In the 2011 off the Pacific coast of Tohoku Earthquake, especially coastal areas of the Pacific Ocean suffered extensive damage by tsunami. Then, there were needs to develop reinforcement methods for existing breakwaters against tsunami force. The authors proposed a method to reinforce a breakwater against tsunami with a steel wall behind the breakwater. This report presents the experimental results of the breakwater reinforcing method. In the proposed method, steel piles are inserted behind the breakwater and rubbles are filled between the caisson and the piles. The model caisson failed in sliding mode without this improvement method. When it was reinforced with steel walls and filling, the horizontal resistance of the model caisson improved effectively. The failure mode of the caisson changed from sliding mode to ground failure mode. By analyzing the bending moment of the steel wall, the stress distribution in the wall from the caisson via filling and the ground was obtained and failure surface of the ground can be estimated.
A large earthquake such as Nankai Trough Earthquake is concerned to occur in the near future and there is fear that coastal levees will sink by liquefaction. Authors proposed installing double sheet-piles into the levee and additionally combining another sheet-pile as a partition wall perpendicular to the extension direction to the levee. It has been confirmed by model tests that this countermeasure is very effective for the deformation/settlement reduction of levees during an earthquake. However, since the partition wall was modelled by the steel plate in the model tests, the effect of the joints between sheet-piles could not be taken into consideration. Authors also reproduced the model test results by using a two-dimensional effective stress analyses (code:LIQCA2D12) with high accuracy. In the numerical study, the slippage effect of joints between sheet-piles for the partition wall was taken into account. As a result, it was confirmed that the shear distortion generated between the joints weakens the constraint of the ground inside double sheet-piles, but in spite of this negative effect, the settlement of levee was reduced down to 15% compared to the case without countermeasure.
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