You see them in every city across the world, but what is a manhole exactly?
Manholes have been around for decades and usually go unnoticed to the average city resident. With around 12 million sewer or stormwater manholes across the United States, these holes play a bigger role than you think.
Covered by a manhole lid, the manhole itself is the shaft channeling through the ground below. Lids are usually made of cast iron, concrete or a combination of the two. Manholes can also be environmentally-friendly materials like fiberglass or plastic which don’t cause ground contamination. These manholes may all look different, but they all serve a similar purpose.
Without manholes, repair, unground developments and general maintenance would be difficult. It doesn’t take much to create these holes and although they may seem simple, manholes are more than meets the eye.
Sometimes referred to as inspection chambers, manholes get their name from serving a similar purpose.
Manholes provide access to sewer systems or other underground facilities. Inspectors and other professionals use these holes to make modifications, provide necessary cleaning and manage routine inspections. The inspection process is somewhat complex, but there are dozens of resources to help you learn more.
The entrance below gives individuals the ability to change the direction or alignment of the sewer below. Manholes help with the development and laying of sewer lines in order for them to work correctly.
Most individuals don’t realize manholes allow a sizable amount of gases through the slits in the cover, aiding in sewage ventilation.
Drilling manholes has gotten more and more simple over time.
Once a demanding and unfortunate task, manholes are now complete in seconds thanks to the development of the Giant Hole Saw.
This saw isn’t much different than hole saws of the past, but the scale and advancements make the job ten times easier. Donned with a cutting head five feet in diameter and the ability to drill through 14 inches of concrete in 90 seconds, the Giant Hole Saw breezes through layers of street and asphalt.
The saw fills in the material around it creating grooves and ledges needed for the manhole cover to fit.
The machine is also used to raise old manholes out of the ground in order to make them serviceable again. When the cut is complete, a lifting arm on the hole saw lifts the old manhole cover and concrete out of the hole and a team work on the repair.
Manholes aren’t round for the hell of it. Their circular shape is necessary for a few reasons.
Manufacturing circular manhole lids are much easier than rectangles or squares. The weight of the manhole cover also plays a factor in making them easier to carry or even roll if they’re too heavy. There is no alignment process when putting the lid back on either as the ground covers are easy to slide into place with varying angles.
The biggest reason that manhole covers are round is to erase the fear of the cover falling into the hole below. Thanks to the lip around the rim of the hole, manhole covers can’t fall through the hole no matter their positioning.
Rectangles and squares, unlike circles, can fall diagonally into the hole and cause harm to pedestrians and drivers that may not see a vacant manhole lid without caution tape or cones. This is also a dangerous possibility for workers that are moving manhole lids by hand with a hook as the weight of the cover could drag them into the hole with it.
As redundant as it may seem, individuals who drill a manhole need to consider the type of manhole they’re about to create,
A manhole come in three sizes; shallow, normal and deep.
Shallow manholes are in the range from 75-90 centimeters at the beginning branch sewer or a place free of heavy traffic. These manholes are specially referred to as inspection chambers and have a light cover.
Normal manholes reach a depth of 150 centimeters and have a heavy cover. Deep manholes are when the depth surpasses 150 centimeters and also includes a heavy cover.
Considering the location of installing a manhole is also valuable.
Manholes aren’t drilled into the ground without rhyme or reason. In fact, plans for a manhole depend on a few variables.
They can be drilled when there is a change in the grade, alignment or size of the sewer. Manholes are also introduced at a junction of two or more sewers, but also have a purpose in a straight alignment of sewers depending on the diameter of the sewer at regular intervals.
Placement is also considered in locations that provide easy maintenance access.
They might just be holes in the ground, but manholes still need maintenance.
In fact, it’s said that 80 percent of manholes need maintenance or rehabilitation according to the Public Works Magazine. Manholes need to be maintained for public safety so a regular schedule of checks is recommended.
Manholes should be free of trash and debris both inside, in front of and across the grate’s opening. This includes vegetation, roots, or in some cases, dead animals.
Cracks in the manhole cover ensure proper function as well. Making sure the manhole sits flush on the raised rings will guarantee the safety of individuals who walk over the top of them and limit cracking from uneven weight distribution.
One of the main checks come from the structure itself and making sure the pipes are connected and working.
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