Answer: If cement slurry is found flowing out from the edge of the concrete pile, and the sand and gravel sink after a few minutes, the bottom grabbing phenomenon is the segregation of the concrete mixture.
Segregation is a manifestation of poor workability of concrete, which is easy to block the pipe during pumping and reduce the strength of concrete.
The common cause of segregation is excessive dosage of pumping agent. You can reduce the dosage by 0.2% and try again.