Manholes are the most commonly featured thing which can be seen in a metropolitan city road. You can definitely find that apart from the buzzing traffic, the people of the city streets and alleys, the roads are heavily fitted with heavy-duty manhole covers. In several movies, we can see that lead actor is sprouting from a manhole cover for saving the world from vicious and treacherous villains. But in reality, the manhole covers play a serious play which makes the lives of the civilians much easier.
Manhole, as the name implies is an entry for maintenance personnel from the ground surface into the subterranean world of pipes, cables and utility lines. Installed out of sight, this underground labyrinth of pipes crisscrossing each other is the spine of our cities, keeping them clean and healthy. To keep it running and functioning day and night, regular maintenance and repairs is a must. The purpose of manholes is that every length of pipe is accessible for inspection and maintenance.
Manholes are provided:
Where there is change in pipe diameter in the pipeline
Where drains or pipelines are changing direction
Where drains are changing gradient
At the drain head for each pipe length
At drain junctions that are difficult to clean
Civil engineers in Rome invented the concept of underground sewer to rid their cities of plagues caused by human contact with waste. Their water sources that they used for consumption were also contaminated as they served as open sewers. The underground sewers made sure that that waste stayed out of reach of humans and was deposited by these sewers further downstream. For periodic cleaning, they also provided access ways that were covered with stone lids that we call manholes today. Incidentally, these stone access way covers are still seen in Jerash, Jordan which was a Roman city in the old days.
Heavy-duty manhole covers are made out of glass-reinforced plastics and other composite materials. These manhole covers may be different in form, detail, and composition but the significance and importance are all same. Manholes are made out of cast iron, concrete, or a combination of both. They usually are strong, cost-effective, and heavy. On average a manhole mainly weighs more than 50 kilograms (110 lb). Its huge weight helps to keep them in place when traffic passes over them and makes it difficult for anybody apart from authorized people to remove them without suitable tools.