In the slag formation of a pile foundation engineering of Chengde, dry hole-forming operation could not be applied in extremely thick fill soil layer, double liquid grouting method was used first for consolidation and then dry hole-forming construction was made by rotary drilling rig. The practice shows that this method is feasible in the loose extremely thick fill soil consolidation with good treatment effect. In this case, the ratio and volume of solution are the key factors. The self-stable ability and the bearing capacity of the soil are improved by consolidation.