Foundation treatment method adopted when old residual pile foundation exists during building construction

The invention relates to a foundation treatment method adopted when an old residual pile foundation exists during building construction. The method comprises the steps that 1, a newly-built foundation bottom face is adopted as a base, and overexcavation is carried out towards the lower portion and the two sides; 2, the old pile foundation exposed after overexcavation is chiseled away through a concrete chiseling machine, and exposed steel bars in an old pile are cut away through electrical welding; 3, after the ground obtained after overexcavation is leveled, gravel refilling is carried out, graded gravel with the maximum particle size of 50 mm is adopted for refilling, refilling gravel layers are ground by a vibrating roller layer by layer, the thickness of each layer is 200-300 mm, and the degree of compaction of the refilling gravel layers is not smaller than 0.97; 4, foundation pad layers are laid on the refilling gravel layers, and the strength grade of concrete is not lower than C10; and 5, newly-built