Buried district heating pipelines: Soil-pipe interaction of district heating pipes - Suggested framework

The existing framework regarding the pipe-soil interaction, and some current research options concerning the district heating pipe installation and bearing behavior, are presented. District heating pipe systems consist of three bonded components that include an inner steel pipe, in which the heat medium is transported, a polyurethane (PUR) foam insulation und a coating pipe of high density polyethylene (HDPE). The outer HDPE-coating has to prevent mechanical influences on the insulation foam and must avoid moisture in the foam from groundwater. The axial displacement of a district heating pipeline during operation in arc or junction sections leads to lateral (horizontal) displacements perpendicular to its axis. It causes a bedding resistance of the surrounding soil so safety cushions have been used in such sections to reduce the resistance, and the reaction stresses have sometimes been neglected in the design.