Drainage and Manholes
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Let us travel back in time
History tells us that we all used to literally throw sewerage into the streets, from what we understand, with an open gully running down the centre of the street, which finally, via various ducts, made its way into the sewers, which were typically local streams.
Let us talk about drainage pipes!
The drainage pipe was the invention that took us from open gullies, exposed sewerage systems and rainwater systems, to the more civilised drainage systems that we see today, or to be more precise, don't see today.
Clay drainage pipes
Clay drainage pipes were originally used, being butt-jointed, which means laying them next to each other and which means an element of leakage on very old pipes. These ran as things progressed, socket joints were used, as well as bedding materials. We are generally talking here about four and six inch pipework. Larger drains used hard rope to seal the joints.
Brick pipes
Larger pipes tend to be formed of brick, often used in action films as the escape route, i.e. Teenage Mutant Ninja Turtles. They were originally formed in vitreous clay. Interestingly, the original pipes were far rougher with falls for four inch pipes (100mm), being recommended at 1 in 40 and for six in pipes at 1 in 60, although with modern smoother pipes it is said you can have a fall of 1 in 100.
How is the fall in a drain really worked out?
We would like to recount our very first experience of drains, when we were asked to hold the staff by the surveyor so that he could work the levels out. They didn't work, so when the clerk of works came to check he asked us to put the staff on top of our boot to make it appear as if there was a fall. What we didn't appreciate at the time was that we were an accessory to the property having poor drainage forever and a day
Pitched fibre pipes
We have spoken to a contractor who regularly digs up the ground to replace pipes and he advises that he often finds pitched fibre pipes that have collapsed, or been compressed, by the weight of the earth. They are no longer used and we have just about replaced all the ones that we did use.
Plastic pipes
The most commonly used pipes today for smaller work. Interestingly, when we spoke to the contractor about its use he said that the handling, as they are lighter, was much better and they cut much easier, using a wood saw, whereas in days gone by you had to use a pipe chain to cut clay pipes, which was far harder, we are advised by someone who had to use them.
How do our drainage systems work today?
The systems are generally split into sewerage or foul water and rainwater or surface water.
Combined drainage
In years gone by both the foul water and the rainwater used to be collected and discharged into the same pipework, but as the years have gone on it was decided that it would be best if the two were collected separately. From what we understand, this has a few benefits; the first being that where there has been a heavy downpour there wasn't a back up of sewerage in the system and, secondly, that the sewerage systems didn't spend forever cleaning the relatively clean rainwater and surface water.
Septic tank
It is worth talking about septic tanks, as there are still a lot of these about. We would describe this as your own private drainage arrangement. Septic tanks can be of brick, concrete or modern GRP construction but should all operate on the principle of solids being broken down by bacteria, the partly treated foul water then being disposed of by discharge into adjacent ground by a system of soakaways, land drains or perforated pipes. The solids are then collected.
A brief history of septic tanks
These came originally from literally a hole in the ground. They were then formed in brickwork, some of which were lined, but more recently they have been formed in glass reinforced plastic, where the trade name of Klargester has become almost a household name (like Hoover and Dyson).
Brick septic tanks problems
We have come across problems with brick septic tanks, where they have not been maintained and the joints have weathered over the years. This allows groundwater into tanks, meaning that during the winter months they fill up very quickly. One key feature of septic tanks is the land drains or the drain fields. These are underground pipes that allow the liquids to filter in a designated area. This, of course, very much depends upon the ground they are going into and in clay areas it is usually not considered good practice to have land drains.
Seepage pits
You may, on rare occasions, come across seepage pits. These were the forerunner of the septic tank systems, which are large pits with honeycomb type brickwork, perforated concrete, which allows the sewerage to seep into the ground. Of course, the ground conditions have to be appropriate!
Septic pool
The modern seepage pit, where a property's foul drains discharge to a cesspool, traditionally an underground chamber designed for the storage of foul water. Once the chamber has filled it will require pumping out by the Local Authority or a private contractor.
What are manholes (more commonly known as access chambers) for?
This is a requirement where drains meet, or they turn a corner, as these are likely areas for blockage and it allows an area that can be accessed for inspection.
Brick manholes
Although very common, they are rarity a in new construction works. They are generally considered a pain to carry out the building of the manhole in brick.
We do come across brick manholes where the sides have spalled, we assume due to groundwater pressure, and repairs are needed.
Plastic manholes
The circular plastic manhole; probably more correctly referred to as an access chamber, and you certainly couldn't get down inside it. This has taken over as the most commonly used form of manhole. These arrived with a number of pre-formed pipes.
Concrete ring manholes
Also relatively common, these are pre-cast, pre-formed manhole rings, that you literally just stack on top of each other. The benefits are that you can still form the haunchings, so you can have a tailor made drainage system, in a similar way to the brick manholes.
Drainage tests
Air test
A bung or balloon is used to test the effectiveness of foul water drains. It tends to always be foul water drains, as this is to stop sewerage leaking into the water table level, which would not be good for our drinking water. This involves putting bungs on the ends of the pipes and then filling with air. A manometer is used, which is a u-shaped tube filled with water to see how quickly/slowly the air escapes.
Water test
Again, this is carried out to ensure that sewerage isn't leaking into the ground and therefore into our water table. This is where bungs or balloons are put in to pipes. It is filled up with water to see if the water leaks out.
What are rodding eyes for?
In recent years, possibly for economics, possibly because manholes were considered not necessary, a smaller rodding eye has been used where there would sometimes be a manhole. This does allow drainage rods to clean a blocked drain.
Methods of cleaning the drains
Pig tails, etc, and pressure jetting
We have seen various drainage rods over the years, but the pig tail is the one we remember, which is like a cork screw on the end of the drainage rod and is literally for rodding and cleaning out the drains. We have also heard stories about them being pressure jetted. Pressure jetting works very effectively but sometimes wrecks the joints.
Checking the condition of your drains
Closed circuit TV cameras
We found closed circuit TV cameras to be an excellent way of checking the condition of drains. Firstly, the cameras will look through the drains and you will be offered a report on the condition; any cracks, any joint problems, etc, and at the same time they do actually clean the drain, as it is the only way you can get the camera down, so it is well worth having a closed circuit TV camera report carried out on your drains, particularly if they are old.
You may also be interested in these other articles:
Resolving Dampness in your Basement
Dampness in Buildings - Basics Article
Dampness in Buildings - Technical Article
Dampness Defects Report
Dampness Problems
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