Granular bedding is commonly used as bedding for flexible pipes. Granular material is self-compacting and it helps to reduce the pressure acting on the wall of pipe trench. Granular materials have higher modulus of soil reaction than adjacent in-situ soils and this allows it to carry higher loads than in-situ soils without deformation.
However, for poor in-situ soil conditions, the in-situ soils may not provide adequate lateral support when the flexible bends deform vertically and push the sides of pipe outwards the wall of pipe trench. As such, additional trench width is required so that thicker granular bedding on the sides of trench can be backfilled. As such, the thicker layer of granular bedding enhances the spreading of the force over a larger area so that the strength of poor soils is adequate to support it without failure.
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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