Abstract: Pile runs often occur in the dynamic driving of steel pipe pile in ocean engineering, and it would bring about serious threat to the safety and to cause huge property losses to the engineering activities. Therefore it is of great significance to investigate the trigger mechanism of pile runs for the successful installation of pile foundation. Based on several project cases, this paper analyzed the popular strata condition and the mechanism for pile runs, and summarized the calculation methods for the dynamic skin friction of pile during pile running. It is found that, pile runs always occur in soft clayey soil layer, and can be classified into two categories. The first is hard layer puncture pile runs. In this case, the blow counts and the driving footage are relatively large before pile runs. The second is unstable equilibrium pile runs with less blow counts and driving footage. In either case, owing to the dynamic action in pile driving, the pore water pressure in the clayey layer increases constantly, resulting in a continuous decrease in the shear strength and a continuous loss in the structural strength of the clayey soil. When the soil resistance is not large enough, pile runs will be triggered. In the process of driving piles, the magnitude of the dynamic skin friction of pile will decide to a large extent whether pile drops or not. The dynamic skin friction of pile is often obtained by multiplying the static skin friction of pile by a reduction factor. This factor is closely related to the mechanical characteristics of the soil layer and the driving process, and is always located within [0.05, 0.5].

Key words: ocean engineering, steel pipe pile, pile runs, dynamic skin friction