Underneath-buried shallow-buried bridge expansion device

The invention belongs to the field of bridge construction, and particularly discloses a buried shallow-buried bridge expansion device which is characterized in that a web plate of a middle beam is provided with a connecting hole for a cross beam to penetrate through, the cross beam is welded with the middle beam after penetrating through the connecting hole, and a middle beam reinforcing plate is fixed to the lower end of the middle beam and located under the cross beam; the upper end of the supporting box is lower than the upper end of the middle beam, a limiting hole is formed in the position, located on the upper elastic supporting piece, of the upper end of the supporting box, the upper end of the upper elastic supporting piece is inserted into the through hole and limited by the inner wall of the limiting hole, and a cover plate used for sealing the limiting hole is fixed to the upper end of the supporting box. And the upper end of the cover plate is lower than the upper end of the middle beam. By the ad