Mathematical and Physical Study of Pipe Lines Subjected to Differential Ground Movement

Soil-pipe interaction studies leading to the laboratory observations of the effects of
differential ground movement between a heavy yielding structure and a pipeline firmly connected to
it is presented in this paper. Such differential movements induce excessive stress concentrations on
the pipeline. Plastics pipes fail as a consequence of such movements, though their flexibility should
make them less vulnerable than rigid pipes. In order to evaluate the displacement, bending moment,
shear force, vertical soil resistance at soil pipe interface under these conditions, innovative
experimental techniques were developed and these are described in this paper. The soil resistance on
a pipe section is characterised by the load-displacement behaviour of the embedded pipe section
subjected to lateral displacement, vertical displacement, axial displacement along the axis of the
pipe and rotation about the pipe axis. A mathematical analysis to complement the laboratory studies
is developed and presented by treating the pipelines as a beam on elastic foundation. The magnitude
and location of the maximum bending moments arising from yielding of the heavy structure is
examined. The experimental observations of the behaviour of pipes subjected to such differential
ground movement are compared with the results from the theoretical predictions. The provision of
rocker pipe joints that entertain a permitted rotation helps to redistribute the adverse bending
moments to acceptable levels and thereby alleviate distress in the pipeline. The paper gives results
that demonstrate theoretically and experimentally the appropriateness of the use of flexibly jointed
rocker pipes to prevent such failures. Field examples of the adoption of such joints is also presented
and discussed culminating with the expression of the need for rational design procedures for
pipeline foundations including rocker pipes to be incorporated into codes of practice such as EN
1295 is emphasised.

Citation:
Wijeyesekera, D.C; Reginold, J.T. (2007) ‘Mathematical and Physical Study of Pipe Lines Subjected to Differential Ground Movement’ Proceedings of the AC&T, pp.243-251.