With the increasing of current installed capacity of offshore wind power

super-large diameter steel pipe pile foundation has been widely used. The increase of pile diameter changes the pile-soil interaction mode

thus the applicability of the method for calculating inner frictional resistance of steel pipe piles in the current code is open to question. In this study

centrifugal model tests are carried out to reveal the behavior of earth pressure and internal frictional resistance in clay with different pile diameters by using double-walled pile and pipe pile models. By using finite element numerical analysis method

the factors influencing the inner frictional resistance are analyzed

and a method for calculation of inner frictional resistance of steel pipe piles is developed. The proposed method is verified by comparison with the centrifuge test results. The results show that

with the increase of pile diameter

the inner wall earth pressure increases

and the inner frictional resistance also increases. The inner frictional resistance is exponentially distributed along the pile depth

and it is available within 5 times the pile diameter from the pile tip. The proposed calculation method of inner wall frictional resistance is found to be in good agreement with centrifuge test results.