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Manholes – Research

Mar 2009
26

History:
Channels, or drainage conduits, were created underneath the streets in an effort to keep the waste away from the structures, and allow it to flow away from the residential areas. An initial problem was that the conduits leading away from the structures and to the actual underground drainage channels weren’t actually vertical. They were slanted. And waste didn’t flow easily to the channel, as there was no water pushing it forward. Maintenance workers were frequetly needed to shovel the waste clear of the conduits and into the channels.

However – there was no easy street access to the conduits, meaning the workers would have to either dig their way down, or most likely, enter through the actual toilet hole. The toilets themselves thus became manholes.

Extensive studies over many years were conducted to better determine the form and size of the conduits, and ensure that sanitation workers would have easier access to the system for maintenance.

Street level channels would lead to the waste conduits, giving access to the sewers, while also acting as ventilation to prevent gas build-up. These channels – or manholes – leading to the modern “Underworld” of society, needed obvious covers; easy for workers to access, yet hard for residents to accidentally fall in or steal. Round, cast-iron manhole covers were an efficient choice over square for a few simple reasons.

One reason were the actual conduits – the holes that had been dug and that were fortified with brick (in Victorian times), were cylindrical – the strongest form for the underground purpose (pressure equally distributed). The best fit for a cylinder is quite simply a round cover. Another reason was transportation and installation. Rolling covers could make life easier. Then – the shape could assist preventing the covers from falling in the manholes once removed (although additional ledges under the covers keep them in place).

Manhole Cover Design

Manhole cover design varies greatly from city to city, with each municipality balancing budget versus art. Some cities, such as Seattle, opted for a clever street map design on their covers, others went with city logos or seals. Most, though, choose a simple grid pattern, or checkered design. The reason behind a pattern or design on the covers is simple – traction – both for pedestrians, as for vehicles.

As of late, manhole cover design is no longer something to be treaded on lightly. Cities like Vancouver, Seattle, New York and Tokyo have decided to pursue commissioned designer covers, giving their cities more than just a curiousity. In competitions to find the best designs, these cities have their communities actively participating in waste awareness, while simultaneously promoting a brighter and livelier city.

via manholes.ca

Also in this article, the shape and patterns of several manholes covers are explained: click here


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