Necessity of reinforcement in precast concrete manhole units

Precast concrete manholes are generally constructed by placing the bases of manholes firstly. Walls of precast manholes are formed by placing the precast concrete rings one on top of other up to the required height. Someone can notice that reinforcement used for resisting the lateral earth pressure and surface loads aren't considered in a number of designs. It is discussed in Concrete Pipe Association of Great Britain which analysis of soil pressures shows that standard unreinforced precast units are capable of resisting uniformly distributed pressures (for example loading condition in a manhole) down to a depth of 150m. If very great road traffic and side loads are encountered, an extra concrete surround of about 150mm may be provided.

Fig: A precast concrete manhole