On the radial contact pressure of piggy-back layed buried pipes for district heating

For expansion of district heating networks the focus for construction today is economic pipe laying. Cost reduction potential is still seen in earth works. Accurate and safe design must be coupled with economic, flexible and innovative pipe laying methodologies. Putting supply pipe and retum pipe vertically on top of each other in one trench is a promising pipe laying technology that can lead to a cost reduction. However, only a few investigations are available for the design of district heating pipes in such type of trenches. This paper deals with the contact pressure acting on such "piggy-back" laid buried district heating pipes. The contact pressure from the overburden earth loads is an important parameter, since it affects the friction forces which may be mobilized. It is generally expected that interaction between the pipes themselves and the trench walls increases with a decrease of the distance between the pipes and the trench width, respectively. The present investigation compares radial stresses according to current design directives for buried single pipes with numerically calculated stresses for buried pipes laid side by side and on top of each other.