Why does the pile head break after the concrete is poured into the pile foundation?

After pouring concrete into the pile foundation, the broken pile head mainly breaks the over-poured part of the concrete to expose the anchor bar.

Pile foundation consists of foundation pile and cap connected to the top of pile. If the pile body is completely buried in the soil and the bottom of the pile cap is in contact with the soil, it is called low pile cap pile foundation; If the upper part of the pile body is exposed to the ground and the bottom of the cap is exposed to the ground, it is called high cap pile foundation. Building pile foundation is usually a low pile cap pile foundation. Pile foundation is widely used in high-rise buildings.