The pipeline in its surrounding soil interpreted as a geotechnical structure
The main mechanical function of the soil surrounding the buried pipe is to support the pipeline. Without the soil the pipeline is a very weak and vulnerable structure that then needs artificial supports. On the other hand the soil loads the pipeline as well. Here we will focus on the support function of the soil.
In case the pipe displaces relative to the soil, the soil will provide a counteracting pressure, the soil reaction. For small displacements the soil body around the pipe will perform linear elastically, meaning that the soil reaction is linear dependent on the displacement and in case the pipe displaces in the opposite direction, the soil reaction will diminish in the same way as it has been built up. If the displacement of the pipe becomes larger, the soil skeleton will start to fail. In first instance only a small part, but if the displacement grows further the soil will further fail, until a situation is found where the soil resistance does not grow anymore because the full failure mode of the soil has been reached. This applies for all directions in which the pipe may move, but for the various main displacement directions, the failure modes differ and thus the magnitude of the ultimate soil resistance and the related soil stiffness.
There are four main directions that each have their own failure model, Upward, Sideward, Downward and Axial (translation as well as rotation)
Upward relative pipe displacement
The upward soil resistance results from the failure of the soil wedge above the pipeline.
Sideward relative pipe displacement
The sideward resistance results from the failure of the soil wedge next to the pipeline.
Downward relative pipe displacement
The downward resistance results from the failure of the soil underneath the pipeline.
Axial or rotational movement of pipe
The axial transitional or rotational resistance results from failure of the soil around the circumference of the pipe wall.
PipelineSoil, last changed: 1/13/2020