A device for producing underground cavities, comprising a tubular drive shield adapted to be advanced into the cavity and having an interior support wall, a support member rotatably and axially movable supported on said support wall and having a radially extending arm portion, a gas jet lance supported on said arm portion, nozzle means associated with said gas jet lance directed ahead and transversely of said lance and said shield, means for supplying hot gases to said nozzle means, and means for rotating said support member and for shifting said support axially with said nozzle means to direct the gases therefrom to form an annular slot in the ground ahead of said shield of a size to accommodate said shield, said nozzle means including at least one discharge nozzle discharging axially ahead of said lance, at least one nozzle discharging radially of said lance, operating independently of said axial nozzle.