Testing Research On Load Transfer Mechanism Of Marine Open-ended Steel Pipe Piles

With the development of economics, the appearance of high buildings, large-span bridges and large scale deep water piers make the widely use of open-ended steel pipe piles. However, up to now, the load transfer mechanism of this type of pile is not clear out, and there is lack of experienced parameter of regulations to confirm the bearing capacity.Study on the load transfer mechanism of pile and the bearing properties of open-ended steel pipe pile, and analyzing the static load test results of open-ended steel pipe piles, this paper analyzes the load transfer mechanism of this type of pile. The Q-s curves of the open-ended steel pipe piles are both gentle style and drop style.Using the stress test results, this paper analyzes the distribution of shaft axis force and lateral friction resistance, and the exertion properties of lateral friction resistance and bottom resistance. The research result shows that the distribution of shaft axial force is decreased with the deep of pile, and the exerting of lateral friction resistance is in different levels at different depth. Also, under the ultimate load, the bottom resistance is taking small proportion in bearing capacity of pile.Analyzing the load transfer curve of lateral friction resistance and bottom resistance, this paper make a conclusion that the load transfer model of both lateral friction and bottom resistance are hyperbolic models.The static load test results show that it is not necessary to take into consideration the reducing effect of soil compaction on lateral friction resistance, and the tip pile blocking effect is very weak.Combined with the static load test results, this paper creates trial pile modeling with FLAC3D software, and compare with the test results, the effect of simulation is viable.Analyzing the difference of load transfer mechanisms between open-ended steel pipe pile and closed-ended steel pipe pile, and drawing a conclusion that the Q-s curve of closed-ended pipe pile becomes gentler, and the decay rate is decreasing while the shaft axis force pass down, also the axis force at the pile toe is larger, in addition, the exerting of lateral friction resistance is degradation, further the bottom resistance can reinforce the lateral friction resistance at the pile toe.Analyzing the influence of load transfer mechanisms in isotropic soil while of large open-ended steel pipe pile while its length changed, and drawing a conclusion that with increase of the pile-length, the Q-s curve becomes gentle, and the decay rate is decreasing while the shaft axis force pass down, also the exerting of lateral friction resistance is degradation. For the open-ended steel pipe pile, it is incapable of purely increasing the pile-length to enhance the bearing properties. This type of pile has effective length, and we should choose the appropriate pile-length in design.