There is nothing special to install our BMC/Polymer concrete manhole covers, sewer and drain covers, trench covers, gully gratings and grids inlets, comparing with the installation of iron cast or other types of manhole covers. However due to LESS FLEXIBILITY OF POLYMER MANHOLE COVERS, the installation has to be done more strictly than the cast iron ones for the manhole covers to work better and last longer:
The polymer manhole covers have to be installed properly, especially in busy walkway and driveway. Unfortunately we do not provide the installation services for our manhole covers sold.
The above image shows five kinds of incorrect installation of polymer manhole covers. There may not be any problems if no vehicles access to the places, should the vehicles be driven over the manhole covers installed in such ways, the manhole covers would be damaged and not last longer.
Polymer or BMC manhole covers are not as flexible as cast iron ones, without the support and protection of the surrounding concrete the edges of the cover and frame may be damage if they expose to high "point force", when the wheels "hit" or crash them. When the wheels of vehicle start to move, stop suddenly, or "jump" onto the covers as crash, the wheels apply higher point force to the cover or frame than they roll over as usual. Should such a crash force be over the load capacity of the manhole cover, or the force limitation it can stand, the damage may be caused.
Grid inlets are usually placed together for the long open trench. The load capability of each grid inlet decreases because two sides of the inlet do not get the support from the ground. Incorrect installation of the grid inlets may cause its load capacity to be even less, to our recommended vehicle GVM figure.
The orientation of the grids is important when they are placed on the trench, wrong direction may cause damage as shown in the above image:
Therefore all the above-mentioned three points indicates the major steel bars should be placed in the way to cross over the trench. The concrete bars may be installed under the grid inlets where they join with each other in order to have their full load capability. There is no orientation problem for single grid inlet.
In the above image, the left picture indicates the distribution of force when the wheel rolls over the manhole cover. We find 30% of the force go sidewards, this may explain why the concrete surrounding the manhole covers usually start to be broken earlier, this make the manhole covers not be protected and easily be damaged as shown in the right pictures of the above image. The duty of the concrete mix to be made should be well considered.
A steel framework is recommended to be made and placed along with the manhole cover to strengthen the surrounding concrete, especially for the manhole covers installed in heavy traffic areas such as filling stations. (Shown in the middle pictures of the above image)
There is no maintenance required for the polymer manhole cover itself but the surrounding concrete and the base holding the frame which should be repaired in time if damaged or loosen, before the manhole cover would be broken without its protection and support.
Posted By Admin
The clear opening of the manhole cover (C1 x D1) should NOT be less than the one of manhole (C2 x D2). Should there be no duty required such as in walkway or heavy duty one to be used for medium duty function, two sides of opposite may be less (C1 < C2) while the other two have to be NOT (D1 ≥ D2) if the manhole covers of correct sizes would not be found. It's not recommended to have the manhole covers with shorter clear opening of all sides installed in any situations.
This manhole cover was installed on the driveway, the frame was damaged because it did not have the fully support from the base, one side of the frame apparently hanging over the manhole, i.e., the clear opening of the manhole cover/frame is shorter than the manhole.
I found many times that the polymer covers or grids were placed up side down into the frames on site by the staffs, the back sides are easily broken by the vehicle wheels due to its structure and the thinner material on the framework. The grid inlet wrongly installed with its back upwards in the above image finished just a few months.
Here are the examples of damaged frames due to the incorrect installation 3 and 4 described above. We all know to break into the door, it's more easier to success by kicking than pushing, that's why jumping wheel may cause edge damage especially to the frames while rolling one doesn't.