The utility model provides a work machine for pile foundation engineering, used for enlarging the pre-drilled holes on bored concrete piles so as to increase the bearing capacity of the bored concrete piles. The hole enlarging device has a hydraulic cylinder that is installed on a bracket that is composed of longitudinal beams, an upper circular hoop and a lower circular hoop. The piston of the hydraulic cylinder pushes driving blocks to make hole-enlarging crank arms extrude hole walls, a row of mud frame is simultaneously installed for send the in-extruded mud out of the bracket, and a filling pile that has a plurality of side wings is formed by casting reinforced concrete after the holes are enlarged. Compared with the past filling piles, the utility model can shorten the length of the pile body and save engineering cost by 40% more or less under without changing the bearing capacity of foundation piles.