A manhole is an important part of wastewater management. Manholes are built into an underground drainage system to facilitate inspection, maintenance and repair in the pipes and drains. Manholes are also used for other underground public utilities like water pipes, electricity, telephone and gas lines. Manhole covers were devised to ensure that these openings do not create an unsafe situation for passing pedestrians.
Manhole covers date back to at least the ancient Roman civilisation when heavy blocks of stone were used for the purpose. From stone, today we have FRP manhole covers. Indeed, composite manhole covers are the most in demand today because they are ideally suited for the purpose. There are some critical requirements that any manhole cover must meet:
- Cover the manholes so that passing pedestrians are not in any danger of falling in.
- Be able to withstand heavy traffic of passerby and vehicles.
- Be able to cover a manhole without falling in
- Be able to withstand the underground conditions like fumes from wastewater.
FRP manholes are particularly suited for the job, since these can meet all these requirement, plus some more! Here are some of the reasons composite manholes are better than the rest:
Low Scrap Value
One of the problems with traditional manholes is theft. A surprising number of manholes go missing because these are just simply lifted and taken by thieves. This is because traditional elements like cast iron and other metals have scrap value and hence, an easy source of income. FRP, on the other hand, has no scrap value. They can not be sold as scrap and hence, have no attraction for thieves. In other words, it’s an easy, effective and low cost means of making yourself theft-proof!
Strength
A manhole has to be incredibly strong since it is laid on the ground. It has to withstand heavy pedestrian and vehicular traffic. It must have enough strength to not develop any fractures in with continued and regular use. This is why composites used in FRP manhole covers are of the highest grade in strength. These are always fully traffic rated.
Thermal Resistivity
Manholes that are built for electric or telephone lines are required to be non-conductive. The only material that effectively fits the bill here are composite manholes.
Locking Mechanism
Apart from thieves, manhole covers can also be displaced by number of other reasons like heavy stormwater, flooding, vehicles and sewer backup. Although the older cast iron manholes do have a lock, it can be easily broken by vandals or just go missing due to wear and tear. This leaves the manhole exposed or the cover easy to remove. Composite manholes are designed with an integrated locking mechanism, which cannot be broken easily or even removed accidentally. Even the simplest manhole will have a simple tweak of design — a lip that stops the cover from moving easily.
Resistance To Corrosion
Manholes have to be resistant to the many corrosive elements that are found around. Manholes set on open ground must be able to withstand heat, rain and other such runoff. Then there are the corrosives that run underground. In case of sewer line, it must be able to withstand any splashing of highly corrosive wastewater and the fumes. The earth itself can be corrosive. Most metallic manholes start showing signs of wear and tear quite quickly as these factors take a toll. FRP manhole covers have a decided advantage here because these are resistant to most corrosives. It can be a very durable material.
Less Leakage
Cast iron manholes are designed to be a little loose-fitting. The problem with this is that it allows the stormwater or other drainage water to seep into the underground chamber. This can overburden the drainage system. Where the cover is meant to protect other utilities, like electricity lines, such leakage can be even more dangerous. The tight-fitting a composite manhole are the only foolproof design we have to ensure that such leakage does not occur.
Passing Radio Signals
Where metals and cast iron manholes will interrupt radio signals, FRP manhole covers allow them to pass through. This is a very important in modern manhole monitoring systems where we use radio signals to understand the flow of the water and other components underneath.