The structural capacity of flexible pipes (e.g. plastics and metals) is derived from ring bending stiffness. Owing to creep or relaxation the ring bending stiffness decreases with time. Flexible pipes are liable to failure by excessive vertical deflections, ring bending strain and buckling.
For rigid pipes, the shape of embedment determines the amount of loads on pipes. For trench condition, the side walls of the trench provide frictional support to resist the filling material on top of pipes. For embankment condition, the fill materials on either sides of the pipe settle more than the soils on top of the pipe leading to increased loads on the pipe. However, for flexible pipes, it distort in the vertical direction at least as much as the embedment. The friction effects can hardly be developed to increase the loads on the pipes more than the loads on soil on its top. Hence, the shape of embedment is generally not considered when determining the loads on flexible pipes.
This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.
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