Abstract: A polymer geo-injection apparatus for protecting an underground structure is provided. The apparatus includes: a mechanized vehicle for moving on the ground in order to transport the apparatus while the apparatus forms a subsurface polymer layer that protects the underground structure; a polymer supply tank coupled to the mechanized vehicle and configured to supply solid polymer during the forming of the polymer layer; a polymer melting unit coupled to the mechanized vehicle and configured to receive and melt the supplied solid polymer and to supply the molten polymer during the forming of the polymer layer; and a subsurface ripper coupled to the mechanized vehicle and configured to move through the ground in response to the movement of the mechanized vehicle while receiving and injecting the supplied molten polymer into the ground above the underground structure in order to form the polymer layer and protect the underground structure.