Inspection Covers & Manholes

Inspection Covers & Manholes

There are seemingly very few paving projects that do not have some kind of inspection cover above a wide range of underground services – everything from foul drains to telecom, gas or water, or simply as access to pipes that may require periodic rodding. They come in a variety of sizes, the largest (probably) being Telecom rectangles to circular mains water turn-off points. The manholes they cover may be only a few centimetres, or several metres deep.

Note the load bearing weight shown on the covers. In some driveways, there may be heavy duty cast-iron covers, and these should not be changed without strict examination as to why there were installed in their positions. Load ratings vary from 1.5 to 90 tons.

It is common to see that existing covers are required to be replaced with recessed covers that allow for infilling with block/brick paving (100 – 75mm deep trays) or paving (45 – 75mm deep trays) in order to blend in with the chosen surface materials, and thought must be given to the weights and pressures they may have to contend with.

When surveying and setting out in preparation for a paving project, great care must be taken to ensure these covers are set to levels and falls within the pattern and scope of works. These levels will invariably require falls and crossfalls to cope with water drain-off.

When setting out levels, adjustments may be required to ensure a smooth flow of work, and it these adjustments that can cause many problems, both at the time of working, but also in future, if anything is allowed to enter the pipelines or systems, especially those carrying foul water, as even the smallest item can cause major blockages.

It is all too easy to ‘lose’ a tape measure or pointing trowel into the depths of a pit, only to see them wash away with the next flush of the toilet before you can extricate it. One way to prevent this from happening is to board up the pit using a sheet of plywood. As most pits are not true squares or rectangles, it is very difficult to cut a piece that will fit the dimensions precisely.

Take one suitable sized bicycle inner tube, and pump it up inside the hole, at a point around 30cm deep, as level as possible. (Less shallow if you wish, dependent on how much of an adjustment is required) Pump it up until it is firmly wedged into the corners. Then place a piece of 13mm ply (with a screw eye in the centre for ease of lowering and lifting) over the inner tube, so that it completely fills the void. Photograph the bottom channel before you start any work, as frequently, there will be loose bits of rendering and rubbish on the concrete benching left over from the original build.

Add a second inner tube to the upper side of the plywood, to provide a double seal against any detritus from falling into the chamber. Once you have completed the works (including setting the cover and laying the paving) clean off the plywood, hoovering the board to remove all detritus. Let the air out of the tube, remove it and double check for cleanliness. Remove the ply and second inner tube. Photograph the clean channels to prove that you have not created a mess during operations and to protect yourself from future claims.

It is very rare that the inspection covers will align with your desired laying pattern regarding lines and orientation. Provided that you do not move the majority of the existing frame from its original bed, it is often possible to make slight adjustments to the alignment during the raising/lowering operations, as long as you ensure that the chamber is not compromised.