Gravel feeding mechanism and gravel pile machine

The gravel feeding mechanism comprises a pile pipe, a pneumatic cylinder, a short connecting rod, a long connecting rod, a feeding door, a door frame and a feeding hopper, the door frame is arranged on the inner wall of the pile pipe, the feeding door is installed on the door frame in a hinged mode, the feeding hopper is arranged on one side of the outer wall of the pile pipe, and the pneumatic cylinder is arranged on the portion, above the feeding hopper, of the outer wall of the pile pipe; opening and closing of the feeding door are controlled by jacking and contracting actions of the pneumatic cylinder, and when gravel is injected into the inner cavity of the pile pipe, the pneumatic cylinder jacks the connecting rod and then pushes the feeding door inwards to be opened inwards; when the inner cavity of the pile pipe is inflated and pressurized after gravel filling is completed, the pneumatic cylinder pulls the connecting rod outwards to pull the feeding door to be closed outwards, and the pneumatic cylind