With the increase of platform size

pipe piles with super large diameter and deep penetration are increasingly used in practice. In order to make accurate prediction of pile drivability

it is essential to evaluate the change of the soil properties under pile driving exactly

and it is the premise to predict the pile bearing capacity after pile driving. In order to learn more about the change of clay properties during pile driving

analysis on the pile driving record of 36 piles in Bohai area is conducted. According to the analysis

the soil resistance in the clay layers decreases as the depth increases

and it is very different from that in the sand layer. The FEM method is used to discuss the mechanism of this decrease. The back analysis is carried out to get more information. The results show that the clay properties are affected by the dynamic effect. The undrained shear strength of clay approximately decreases with the increase of thickness of the layer linearly. At the same time

a prediction is conducted based on results

and the result is closer to the pile driving record than that calculated by method normally used today.