1, its main function is to connect the pipe pile into the pile cap, to avoid the hollowness of the pipe pile, to increase its adhesion and friction with the inner hole of the pipe pile, and the steel bar of the filling core also extends into the pile cap, so that the pile cap concrete poured subsequently can be effectively and reliably connected with the pile head through the expanded reinforced concrete of the filling core to prevent the pile head from shifting and falling off.

For pressure-bearing piles, its function is mainly to improve the stress state of the pile top, which is beneficial to the connection between the pile and the cap. For uplift piles, it is also necessary to transfer the uplift force evenly to the pile body.