Concrete surround is normally adopted for rigid drainage pipes to resist high traffic loads (e.g. under shallow covers) and to allow for using pipes with lower strength. Moreover, the use of concrete surround can minimize settlement of adjacent structures. In addition, the highest possible accuracy in levels and gradient can be achieved by using concrete surround as considerable settlement is expected in other types of beddings like granular bedding.
The distribution of reinforcement in concrete pipes may not be uniform owing to the occurrence of tensile stresses in different locations around the circumference of the pipes. For instance, tensile stresses are highest at the inner face of pipes at invert and crown levels and at the outer face of the two sides of pipes. An elliptical cage may be designed in order to optimize the usage of steel reinforcement.
This question is taken from book named β A Self Learning Manual β Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.
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