Building Chambers
Digging for a small chamber is not really any easier than digging a large chamber, a digger is designed to dig a rectangle not a circle.
Remember you do not have to follow the spreadsheet recommendation rigidly, you are allowed to think. It may be necessary to upgrade a small chamber to a large one if it is a place where it might get driven over or where Limousin bulls stomp around. The recommended size of chamber is based on the size of the bullet that goes in it, so if there are a large number of spurs, or a fibre count change, then it will need a large chamber. And if a chamber is really busy it might need an extra segment added. Also, if a large chamber is needed mainly for a fibre change and there are hardly any spurs, then you could get by with just 3 sections if you had to (we had one or two reach bedrock for example).
When a chamber is dug there will be a lot of soil left over. On a hillside, this can usually be used for landscaping, otherwise maybe there is an obvious gateway or hollow around that can take some extra. This should be something the diggerman is used to dealing with. In an urban situation it may have to be taken away entirely. Putting a chamber on a slope probably means the chamber has to tilt slightly down the slope for it to blend in more naturally, just looking at it will tell you the right positioning, a spirit level will not.
Chamber preparation – two parallel saw cuts about 100 mm deep, remove section with hammer. Can be done on site or pre-cut. But if you pre-cut them, have the right tools with you when you install the chamber just in case you need to adjust the hole positions.
A small neat hole circular hole cut with a drill attachment seems a good idea, but is not as good as a nice large rectangular chunk knocked out with a hammer (LCH). The LCH method gives you a chamber section that is easier to assemble with the duct and gives maneuverability for the duct when settlement occurs. It is also very quick. There is a rubber seal on the small chambers, this just makes it difficult to assemble the sections - as the chamber is not waterproof, this rubber ring can be taken off and discarded.
A chamber is only a compartment for spare coils of fibre and for a watertight bullet, it does not expect to be a dry chamber, and in fact some chambers spend a lot of time being full to the brim with water. (The bullet only contains fibre joins, so that could still leak and function)
Installing a chamber
It is useful to have a marker on your spade handle to indicate the depth of the hole needed for a chamber. A metre and a half of 16mm spare is more than sufficient at the chamber, anything more than that is unhelpful. The 7 mm ducts ends should ideally all be the same length and be able to reach to a convenient place for B4RN's horse box trailer, so several metres will be needed, the longer the better. B4RN will sort it to their liking when they arrive, they will join pieces on if necessary. Coiling this lot up can be difficult, especially as you really want all this inside the chamber with the lid back on before you backfill round the chamber.
Watch out for the duct wanting to bend down where it enters the chamber as the backfilling occurs. It may need a careful bit of handwork or footwork for tamping down. Standing on the chamber lid as it is being backfilled stops the chamber tipping to one side or the sections separating.
We have always tried to finish off a chamber in one go, installing it and backfilling on the same visit. This works best if all your ducts in and out are ready waiting. (There would be no point putting the chamber in before at least some of them are ready) If there are still ducts to come, then you should prepare the entry hole for them and either, leave a section of outer duct poking into that hole so that the orange duct can be fed in later, or stuff a couple of feed bags down next to the correct chamber hole so that that section can easily be re-excavated when you are ready. Make sure there is no access left available for mice to get in though!
(At some later stage of building you may have to deal with a fully loaded live chamber – one with a mass of ducts and a working bullet. It will be daunting at first to touch any of this, but confidence will grow - you really need to see a B4RN person doing it first, he will have no hesitation in grabbing and pulling it all out. If you ease everything out gradually it will come to no harm. Getting it all back in will be trickier, make sure you don’t trap anything under the lid.)
Bases. It sometimes seems wrong to just plomp chambers on top of soil, but since chambers are not meant to be watertight it does not matter. The bullet is the part intended to be watertight. Things will get slightly grubby if a chamber floods but the manhole is not meant to be visited many times in its lifetime. Concrete platforms have been suggested. Gravel has been added by some people to make a base, but this is not necessary. Ground-control fabric has even been mentioned. A circle of cardboard or adding newspaper would be as effective. There is no light, nothing will grow in the manhole.
A lot of soil to get rid of, mainly because it was dug too deep. We had to add an extra section in the end. The soil was spread along the wall base.
The diggerman is peeling back the turf further along the wall so he can tuck some of the excess soil under it. (Not his field, got to leave it tidy)
A neat urban example, where the soil had to be carted away.
Here the excess soil has been spread out in the corner of the field
We had no chamber available so we just left the hole. And had to install it because of sheep, when it was this full.
Several duct directions from a chamber can make it complicated and messy
After time the manhole will blend in and can get completely overgrown
It's easier to dig a rectangular hole than a circular hole.
Two vertical cuts, then hit the section with a hammer
Someone took our rectangular slot idea a bit too far
The small chamber is notched in the same way.
It's easier to dig a rectangular hole than a circular hole.
They can take a lot of storage space, but they can be left outdoors.
A lot of people cut holes in chambers using this method, it's fine, as long as they know about the other method of just using a handsaw - which has some advantages.
Getting a manhole exactly at the right height is not easy. Too low is better than too high. Some chambers never have to be visited again if all the spurs are connected into the bullet, so it can get overgrown without a problem.
Again a perfect height. It's easier in a flat field, on a slope it never looks quite right.
This one is going to end up high. You may have some landscaping in mind or you may be able to get away with 1 ring less (in some cases, maybe not here)
If you don't screw the frame to the chamber, then anything can happen.
A 5 ring chamber, With that number of ducts, it would be crowded with only 4.
B4RN used to supply frames ready assembled
this will be too high
gravel base
That's okay. Apart from the fact it's upside-down.
Virtually all the small chambers we have put in have had the lid frames screwed on at the last moment. And every time you wish this had been done well beforehand. That would have eliminated this fault.
Related faults
- not screwing lid on properly (- the supplied screws are not very good)
- losing the lid screws
- not having thought ahead as to the side holes
This looks as though it is going to be a bit low. It will be a tough job to raise it, and you wouldn't bother. You might do a bit of landscaping, but the simplest solution is to add another segment. You will probably find it fairly difficult to dig round to lift just that one top segment, it will be easier to unscrew the frame and put the new segment at the top.
A reminder that you don't blindly stick a small round chamber in a field because it 'says so on the Spreadsheet'. You upgrade it to a Large if it is likely to have traffic go over it, or bloody great bulls.
Just decide, don't fuss about clearing the decision with B4RN. Just send Edward a note saying it is now a large chamber.
Cut a slot out of your chamber side, don't make a circular hole. It's easy. Two parallel cuts with a saw and knock the segment out with a hammer. It makes it a lot lot easier to get the duct into the chamber.
In this case it's going to be really difficult to get those ducts through circular holes. If you have a slotted chamber section, then you feed all your ducts into the chamber and then place the next section over them
This is the actual chamber section that they used as the second section.
Chamber segments are really strong and overlap a bit, you could cut a whole section out from the side of a chamber and it would be just as solid. If the hole was huge it would allow unnecessary dirt to seep into it, that is the limiting factor in hole size.
(In this case you could cut your slot at an angle to make it easier for the ducts to enter the chamber)
Small or Large Chamber? It may be listed as a Small Chamber on your Spreadsheet, but this is based mainly on what size bullet it will need to house.
If the chamber is in an area used by vehicles you should put in a Large Chamber. Also the fibre blowing operations can easily be carried out from over a wall, so you may be able to locate a chamber in the next field and still use a Small Chamber. Here they are installing a small chamber in what appears to be a car park.
Bases for Chambers. It sometimes seems wrong to just plomp chambers on top of soil, but since chambers are not meant to be watertight it does not matter. It will get water and dirt entering from the duct holes in the sides. The bullet is the part intended to be watertight. Things will get slightly grubby if a chamber floods but the manhole is not meant to be visited many times in its lifetime. Concrete platforms have been suggested. Gravel has been added by some people to make a base, but this is not necessary. Ground-control fabric has even been mentioned. A circle or rectangle of cardboard or newspaper would be as effective. There is no light, nothing will grow in the manhole.
Not sure what this chamber is actually doing (- blowing chamber maybe?)
Adding extra protection where the orange ducts enter the chamber
You may have been told to be careful back-filling in this area in case the duct eventually kinks as the back-fill consolidates over time. It can and does. The soil pushes down on the duct outside of the chamber and the duct bends over the chamber edge. You will have noticed how impossible it is to fill round a chamber - there are always air gaps when you leave it - these slowly fill up as time goes on.
Adding just a short collar at the entry point is easy, Odd bits of 25mm fit over 16 mm, and you will have some bits of 16 around to go over the 7s.
Water in duct
If water gets into the 7mm duct then the fibre will not blow freely. The house fibre is flimsier than the core fibre and sticks to the side of the duct, sometimes making the process grind to a halt.
It is unlikely to have got in at the chamber end. But there are many houses that are below the height of a chamber and syphons can start. Once you have a syphon then debris also enters the duct. In the chamber you have 6 metres of duct in a coil, air pockets will generally stop water getting in there even if the duct was unsealed and the chamber was permanently flooded to the brim. (It is better advice to tell people to try to leave coils in the chamber as vertical as possible this helps create air pockets to stop water entering)
Water can have got in during construction, a spare end left untaped for a while, a join you had no choice but to make quickly underwater in a flooded trench – these are bound to occur sometimes. You will pay the price on blowing day.
Water is also likely to get into the duct at the householder’s end. You are leaving a coil of duct with an inexperienced person who hasn’t seen your Powerpoint Presentation. You may have left a coil flat on the ground to be less obtrusive, but water can get in more easily in a horizontal coil and this coil may be there for months, leave the coil vertical if possible.
If you leave him with an end-cap then that can easily pull off, so you have to leave it taped over the top of the end cap. Whatever you do you have still left this person out of your watchful eye. You may never meet this person or the person installing the house end. But is this end of the proceedings you should be concentrating on by leaving clear short instructions, verbally and written.
You are a volunteer. You do your best. Water will sometimes get in. It doesn’t happen often. It’s a nuisance when it does.