Study on the Application of Dynamic Stiffness Method in Rock-embedded Pipe Pile End Reinforcement Test

When pre-bored or center-dug method is used to construct rock-embedded prestressed pipe piles, there exists the problem that it is difficult to clean up the slag at the bottom of the pile, and the over-thickness of the slag at the bottom of the borehole seriously restricts the performance of the bearing capacity of the pile end. This paper proposes the construction method of using heavy hammer tamping to reinforce the pile bottom slag, carries out the foot-size model test, and uses the dynamic stiffness method to compare and analyze the characteristics of the change of pile bearing capacity before and after the reinforcement construction. The tests showed that the use of heavy hammer tamping and concrete pouring at the pile end could ensure that the pile end was closely connected with the hard holding layer, and the dynamic stiffness of the pile base was increased by 67%~175% after the tamping reinforcement. In addition, the on-site testing method and concrete pouring construction will affect the dynamic stiffness, and the dynamic stiffness method is used to test the bearing capacity of pile foundation with full consideration of the impact of the testing conditions and construction methods on the testing accuracy.