Measurement of normal pressures and friction forces acting on buried pipes subjected to cyclic axial displacements in laboratory experiments

The earth pressure acting on buried pipes is decisive for the pipe design. For pipes shifting in the ground, such as district heating pipes, which are subjected to cyclic temperature loading, the mobilizable friction force, which is also dependent on the earth pressure load, is a very important quantity. Friction force changes with cyclic axial displacement of a pipeline in operation. A special testing device was designed to investigate the friction forces and the normal pressures on a pipe buried in sand and how these change during cyclic axial displacement dependent on system and soil parameters. The experimental setup is presented, and in particular the application of the tactile pressure sensor, the special measuring technique used, is described. The dependence of the decrease in friction force on pipe diameter, soil overburden height, and relative density of the soil was investigated in the tests. The results are presented and the findings are discussed.