The surface settlements are uneven after improving the surface-layer of the newly hydraulic mud fill and the named “soil piles” are usually produced. Based on the monitored data of pore water pressure and CPT in the soft foundation treatment engineering, this paper analyzes the formation mechanism of soil piles. It is shown that the soil piles are essentially caused by the uneven settlement between the soil around the plastic drainage plates, and the figure of pile seems to be an inverted cone and the cross section is in shape of ellipse approximately. The depth of piles is less than 1.6 m, and the strength of the soil beneath 1.6 m is more even. In the horizontal direction, the strength of soil decreases as the distance to the plastic drainage plates increases. The research indicates that the numerical results agreed well with the facts observed in the field when considering the variations of the soil parameters with the consolidation process. The advices of avoiding or decreasing soil piles are put forward and the conclusions would be helpful for similar engineerings.