Forming a new inspection chamber

[Adrawk]

Following on from my salt glazed pipe thread this one should be interesting. My negotiation with the water company didn't go very well. They are happy with the size of the inspection chamber being 600 x 450 as opposed to the monster specified needlessly on my design drawings.

My problem is they will under no circumstances countenance plastic being on the main drain run. I can either go brick built or precast concrete and I think the 300mm deep 600 x 450 sections may be just about managable with some help at 80kg or so.

So, how the hell do I form a new inspection chamber with all the required benching and pipe connections whilst having a live sewer running through the space I'm going to be working in. Does anyone have any experience in doing such a job? I'd love some guidance.

 

[John D v2.0]

Not sure how many people feed into it? You could always knock on a few doors, ask people not to flush for a day. Ours is only us and next door so we could do it easily, but it could get silly.

 

[Adrawk]

I haven't noticed too much running through it to be honest, I spent my entire weekend last week digging around it and didn't really hear/see too much going through it.

 

[noseall]

First dig a mahoosive hole and expose the pipe completely (full depth) and excavate 100mm of material beneath it. Your hole will need to be as big as the external size of the manhole (MH) plus some wriggle room.

Buy 150mm clay channel complete with channel junctions as necessary. Buy a 6" drain plug. Hire an angle grinder. Mix up a couple of barrows of strong semi dry concrete. At 9:30 a.m. Cut through the pipe at two points about 500mm apart, thus removing a 500mm section of pipe (the size of the cut out should be 100mm less than the inner width of the MH section). Fit your drain plug on the upstream pipe.

Fill the excavated area with the semi dry concrete on the whole footprint of the MH including the area between the pipe cut-out. This forms your MH base. Place the channel and junctions so they butt up snug against the cut-out sections of pipe. When satisfied with their positioning, ensure that the channel invert runs through in line with the invert of the existing pipe each side (upstream and downstream). Then carefully pack more semi dry concrete around the channels ensuring a full fill. It is wise to add a bit of concrete sand (sharp sand) and a bit more cement to the mix for this packing procedure.

Fit small lengths of pipe onto your channel junctions or connect to any existing pipes as necessary, so that they are long enough to exit the footprint of the MH.

Next, cut two slots out of the first MH section (up and downstream) and any other pipes entering onto your channel junction/s. You should have about 50mm or so of pipe protruding into the MH. Mix up some strong firm mortar and bed the first MH section over the pipes and onto your base concrete. You can now bench around the pipes using a mixture of concrete, sharp sand and strong mortar mixed together. Don't cheat on the cement.

Release the stopper as late as you possibly dare.

You can fit the remaining sections and lid at your leisure or do it on the day. Don't forget to release the stopper before fitting the remaining sections!

 

[stuart45]

Release the stopper as late as you possibly dare.

And keep your face well out the way.

 

[bernardgreen]

My negotiation with the water company didn't go very well.

If other houses are served by this sewer then it is the responsibility of the Water Company to maintain it, not yours even if it is on your land.

Relocation may not be classed as maintainance by your local Water Company but the work on the shared sewer has to be done by a person the Water Authority accept as being competent, such as their own staff or approved contractors.

If anything goes wrong and the Water Company have to come out to restore sewage service to your neighbours then it would be expensive for the person who altered the shared sewage system

 

[r896neo]

Just one thing to add to nosealls excellent post, put a rope on the bung for the final release...

 

[noseall]

And keep your face well out the way.

You can release the fluids first via a small central vent before freeing the whole stopper.

 

[Nige F]

You can release the fluids first via a small central vent before freeing the whole stopper.

Unless there is a golf ball sized/hardness t urd amongst the fluids

 

[stuart45]

I prefer the inflatible bungs, or get the labourer to release it.

 

[mfarrow]

I did this on my own, smaller connection (branch versus manhole) and using my own 4.5" angle grinder.

I took the top off first then angle grinded the bottom half from the inside. It worked quite well, and I'd suggest packing something under the pipe to stop it snapping at an unforgiving point (e.g. with a huge shard missing/cracked under a retained section)!

 

[Adrawk]

I'm considering doing this at the weekend weather permitting. The socketed channels, do they allow the rocker pipes to be seated nicely to ensure the invert isnt misaligned?

The plain ends of the channel just butt up to each other then?

So I'll have 2 x straight and 1 x oblique double junction to give me the outlets I need. That also reminds me that I'll need 100mm pipe for my own services too.

 

[tomfe]

You'd be better off hiring a pipe cutter rather than a angle grinder, you will struggle to get all the way around the pipe with just 100mm cutting, unless you get a ring saw.
You could get some quick drying cement to grout your pipe joints in the channel.
You should really use a grano mix for the benching, I use some SBR in their too.

This can be a really stressful job nothing worse than people jot being about to use the toilet!

 

[Adrawk]

I'm going to hire a pipe cutter for the new pipe cuts but the older salt glaze stuff I'm concerned any small hard to see fractures could end up in it shattering and me chasing the pipe into the next properties garden! I think a couple of new grinder blades and a slow and steady approach for the salt glaze is in order.

Just looked up grano and SBR, it sounds like that could be perfect to get the benching spot on. They didn't teach me how to get cement nice and smooth in electrician school

Again thank you to everyone who has contributed to this thread. I might begin to post some pictures of my progress with the extension once it actually gets moving.

 

[Adrawk]

One last question, I hope.

The salt glaze is currently situated in a fashion that will mean a joint will be in the inspection chamber. Would it be advisable to renew the pipe and work with the new stuff?

That would allow me get rocker pipes in place a lot easier too. A couple of people I've spoken to reckon rocker pipes aren't necessary. These are people who reckon they are experienced.