After the water bored pile is poured and the conduit is pulled out, the concrete at the top of the pile sinks and the core of the pile is poured. What is the reason and how to deal with it?

The reason why the pile center won the prize may be that the concrete slurry was separated from the coarse aggregate during tube drawing, and the concrete self-compacting cement slurry appeared; Aggregate sinking, mainly because the tube is drawn too fast, and some concrete below is not dense enough; The slump of concrete is too large, which will also happen when pouring.