Soil Burial Tests: Effect of Soil Burial Exposure on the Properties of Plastics for Wire and Cable

A .soil burial study was undertaken on polyethylene and vinyl chloride plastics in order to develop a background of knowledge concerning these materials t h a t would be useful in the design of buried wire and cable. These plastics were selected for study because of their wide acceptance as coatings on communications wire and cable and because their chemical structure suggested t h a t they might be expected to possess good resistance to soil burial. In the initial phase of this program, wires with extruded plastic coatings on copper and aluminum conductors were buried at the Georgia and New Mexico test sites. Half of the samples were exposed with a 48-volt positive dc potential on the conductors and half without 63 64 T H E BELL SYSTEM T E C H N I C A L JOURNAL, JANUARY 1972 it. An interim report on the vinyl plastics in these tests was made at the end of four years of soil burial. 1 The observations at that time indicated that the nature of the conductor, potential, and variations in the depth of burial (within the limits studied) were not critical variables. On the basis of these observations, it was decided, henceforth, to examine only coatings on copper conductor without potential from a mean depth. In the second phase of this program, molded sheet samples of vinyl plastics were buried mounted on polyethylene tubes. These were introduced because they permitted the preparation of samples from small roller mill mixed lots which facilitated the study of compositional variables.