How can plastics manholes withstand traffic loads?
Traffic loads onto the top cover are not supported by the plastic manhole but by the compacted soil around the manhole.
- The cast iron cover will be often placed directly on the concrete manhole body ring. The traffic loads are transferred directly to the manhole construction. Concrete “accumulates” all stresses in the construction which will break if over loaded.
- Contrary to that is the stiffness of plastic manholes which is smaller than the stiffness of the compacted soil surrounding the manhole. Traffic loads are therefore supported by the soil. Settling of the surrounding soil has no negative effect on the behaviour of the plastic manhole; they follow the movements of the soil, contrary to the behaviour of rigid concrete manholes, similar to the well proven behaviour of plastic pipes.
- Telescoping solutions used in plastic manholes allow small movements to reduce stresses further.
- For the best installation a good compacted layer of sand or gravel is necessary to secure an equal spread of the load from the traffic. The best degree of consolidation is achieved by backfilling in layers around the plastic manhole.
Want to know more? Refer to Manufacturers documentation.