Replacing a manhole cover in the carriageway, step by step

Replacing a cover and adjusting its height are two different jobs, although they look similar and often go together. Adjustment changes the seating level. Replacement means taking off the frame and lid, because the part is damaged or does not match the load.

How do you know a cover is due for replacement?

The lid knocks as traffic passes, so it is working in its seat and breaking up the frame.
A visible crack in the cast iron body, or a loss on the edge of the seat.
The frame turns or shifts relative to the load-relief ring.
A load class lower than the traffic on the road, for example B125 in a carriageway.
A ring of cracking in the surface that comes back after every repair.

The last one is most often mistaken for a surface problem. If the cracking returns in the same place, the cause usually sits in the seating, not in the asphalt.

What class to look for?

Manhole covers are classified by EN 124. In road and street carriageways class D400 is normally used, that is a test load of 400 kN. Lower classes are intended for pavements, car parks and kerbside zones, higher ones for industrial yards and heavy traffic.

Dropping to a lower class to fit the budget saves money for one season. A cover that does not match the traffic breaks up its own seat and comes back for replacement together with the surface around it.

How does the job run?

Signing and securing the work area, closing the lane if required.
Opening the surface around the cover through the wearing and binder courses.
Lifting the material out and exposing the frame and the load-relief ring.
Removing the old frame and lid, assessing the condition of the ring and the shaft.
Seating the new frame at the correct level, on rapid-setting mortar or with a mortar-free system.
Restoring the surface in layers, compacting, sealing the joint.
Checking it is flush with the surface and reopening to traffic.

Where does it usually go wrong?

Too large a demolition area

The bigger the opening, the longer the joint perimeter and the more places where water can get between the old and the new asphalt. Breaking out with a hammer almost always takes more surface than replacing the frame requires.

A ragged edge

New asphalt needs a vertical wall to bond to. An edge left by a hammer is irregular and weakened by micro-cracks, so the joint works from the first frost. Mechanical cutting, straight or circular, solves that at source.

A damaged load-relief ring

The ring transfers load from the frame to the structure of the shaft. If it is chipped during demolition, the new cover will settle despite correct installation. That is why bearing the tool on the manhole frame rather than on the surrounding surface matters practically, not aesthetically.

Compaction in the ring around the frame

The narrow ring of material around the new frame is the hardest place to compact in the whole repair. The smaller and more regular the opening, the easier that ring is to close.

HornetCut R650 opens the surface to a depth of 100 mm in one pass around the rim, on diameters from 1100 to 1300 mm, for manholes from 500 to 900 mm.

How long does it take?

The time for replacing the frame and lid itself is fairly constant and depends on whether the level is set on mortar or with a mortar-free system. The variable that really decides how long the lane stays closed is opening and restoring the surface. That is where the hours are worth looking for.