Vitrified underground structures

This patent describes a method for making vitrified underground structures. It comprises: inserting at least one pair of electrodes into soil in the ground at spaced positions from one another; providing an initial electrically conductive resistance path in the soil across the electrodes; providing a passive electrode in the form of an electrically conductive material; passing electrical current through the electrically conductive resistance path; continuing application of current to the electrodes until the soil between them and immediately adjacent to them has been melted; and terminating application of current to the electrodes to permit cooling and solidification of substantially all the melted soil in situ between the electrode positions into a solid planar mass