Construction method for underpinning of overpass framework pier columns

The invention discloses a construction method for underpinning of overpass framework pier columns. The construction method comprises the following steps of construction of foundation piles, construction of vertical columns, construction of temporary support pier columns, jacking of original box girders, construction of transverse beams, construction of cushion stones, and installation of support seats; during construction, firstly installing the foundation files, the vertical columns and the temporary support pier columns, jacking the original box girder, supporting the original box girder on the temporary pier, disengaging the original box girder from the lower structure, detaching a support seat of the original box girder, breaking down the original independent column pier, building a scaffold to construct a transverse beam and support seat cushion stone, completing the new framework structure, reinstalling the support seat, resetting the original box girder, and carrying out the equivalent-force replacement of the new structure and the original independent column pier. The method has the advantages that the construction method of safely jacking the bridge and replacing the pier columns is realized, the mechanical degree is high, the construction is standard, and the guarantee function on the period, quality and safety of modification construction of pier columns of the highway bridges is realized.