Plastic pipes used in gas utility distribution lines have relatively small diameters and they are buried at relatively shallow depths, usually less than one meter below the ground surface. All existing methods used for estimating plastic pipe deformations are approximate and not well suited for small diameter piping. Applicability of ring-deflection theory in determining plastic pipe deformations was investigated. Laboratory tests were performed to monitor the deformation of high density polyethylene pipes during burial. Diameter changes of the pipes during burial in sand box were monitored using an instrumentation cage. Pipe diameter changes from ring-deflection theory and diameter changes measured during the laboratory tests are presented.