Effect of Strength of Concrete Bulb on Resistance Characteristics at Pile Toe of Steel Pipe Pile on a Thin Layer

摘要

In Japan, steel pipe piles installed using the inner excavationmethod have been widely used as one of the typical foundationsof large-scale structures. In these types of piles, a concrete bulbis constructed at the pile toe by mixing installed concretes withsoils in the bearing ground. As a result, the load-bearingresistance at the pile toe must be affected by the mechanicalcharacteristics of the concrete bulbs. In this paper, the effect ofthe strength of the concrete bulb on the resistance characteristicsat the toe of a steel pipe pile on a thin layer is elucidated througha series of numerical simulations. First, a field loading test ofsteel pipe piles with concrete bulbs on a thin load-bearing layeris reproduced through numerical simulations, to confirm theavailability. Second, a series of numerical simulations arecarried out in which both the strength of the concrete bulb andthe thickness of the load-bearing layer are chosen as variableparameters. The results of the numerical simulations show thatthe yielding that takes place as a result of the relationshipbetween the resistance and the displacement at the pile toe isdominated not only by punching shear failure in the thin loadbearinglayer, but also by the failure of the concrete bulb.Finally, a design chart is proposed that shows the relationshipbetween the unit-bearing resistance at the pile toe and thethickness of the load-bearing layer, in which the effect of thestrength of the concrete bulb on the bearing resistance can beconsidered.