Rerouting A Sewer

[thomp1983]

Hi All,

As seen in the photo I need to reroute a sewer, the one located between points 1 and 2, this will need rerouting to follow the blue line from 2 to 4 back to 1.

I've zero experience of doing this so need some help, the sewer at point 2 is approx. 1.4m deep so I know I need to dig down that far to uncover the existing pipe, I will then need to dig a trench to point 4, What kind of inspection chamber do I need at point 4 to turn the flow 90 degrees towards point 1 and at what depth does it need to be?

Point 1 is approx. 2m deep, do I need to dig the trench from point 4 in a slope down to 2m or can I dig it at a shallower decline and come into the existing manhole at a higher point?

Thanks
Chris

 

[noseall]

IC's 1 and 2 Will likely need re-building if they are concrete haunched fellas. We'd replace it all in 150mm plastic (expensive), so your new chamber (4) would be plastic too.

The border fencing may not like having a 1.5m - 1.8 m trench running close by it though. A lot of digging but not a problem for a 3 tonner. Your extension foundations are going to be deeper than the standard 1m also.

Look out for incoming services. We'd definitely scan that lot first.

You will likely need some temporary Heras fencing along the footpath from IC 4 up to the street sign.
There is going to be a LOT of spoil. Some will need to be rid of but a fair chunk will need to stored. You'll need a fair tonnage of pea gravel and tonne of ballast (for the IC bases) on site. If you are clever with deliveries, you could have the pea gravel dropped straight over the pipes. All you do it cut a modest slit in the tonne bag and let the driver do the rest.

Assuming its all live as follows:

IC 1 could be grubbed out and re-built in plastic with a clever temporary diversion on the incoming so that the existing red branches in on the new light blue line. IC 2 could also be re-built the same, so that it continues to drain via the red line but out via the blue exit and is ready for when that is chopped off. Then it's just a case of digging the new blue line then doing a swap over. It would mean buying two 45 degree branches and a few extra bends that will ultimately be scrapped.

You will need a 150mm drain stopper...

Poo2

• noseall
• 9 Jun 2020

 

[bernardgreen]

There appears to be two incoming sewers from adjacent properties. If this is the case then the sewers on your property are public sewers and the responsibility of the local water company.

 

[thomp1983]

In total there are 5 other houses that join into manhole 2 besides mine, 4 come from the right in the photo and the one from the bottom.

Severn trent are aware of my plan to alter the sewer I have a build over agreement in place to do so as they won't allow me to build over the current sewer and I wouldn't want to incase of future issues.

 

[noseall]

You're welcome Chris. Let me know if you want it building for free too.

 

[thomp1983]

You're welcome Chris. Let me know if you want it building for free too.

steady on now, I work nights so Ive been in bed most of the day and dealing with the plasterer for the rest before coming back to work, appropriate thanks have now been given

 

[thomp1983]

That's the inside of manhole 1

That's the inside of manhole 2

 

[noseall]

Massive, almost civil type job and loads of gear to move both for the drains and for the extension. You could end up spending more than £20 - 30k before you even get out of the ground.

 

[thomp1983]

Not the best news, so what options do I have or is building my extension over the current pipe the best choice?

And why couldn't I just dig down to the existing pipe, cut into it and using an adapter run plastic pipe as shown by the blue line? I guess what I mean is why do I need to alter the 2 existing manholes themselves?

 

[noseall]

what I mean is why do I need to alter the 2 existing manholes themselves?

You may get away with leaving IC 1 unmolested, with some clever swept bends, but IC 2 looks like it would need the haunch-work redesigning. Not an easy undertaking and virtually impossible on a live sewer and at that depth.

 

[thomp1983]

I'm assuming the issue at no2 is that I'm needing to make a new hole in the manhole to change direction that would then need correctly sealed to ensure no future issues which as you've stated is difficult with 6 houses waste to control

 

[thomp1983]

Would it be possible to build a new manhole south of no2 and sweep the pipe from the east into it and then have the new exit run to where I needed it? Then I would only need to control the waste from the neighbour behind my property whilst doing the work?

 

[Hugh Jaleak]

Anything is possible, it's what is allowable. I think you're going to be Governed by what Severn Trent want, so see what their specification is for manholes before getting too carried away. If they are to adopt the new runs and maintain them going forward, they'll want it done properly so it doesn't leave them with an ongoing headache (and expense).

I agree with Noseall, that is a large amount of work to do, and it's not for the faint hearted to tackle. Trenches are going to need support, you've got to get falls right on new pipework, (or there will soon be a problem), and as it requires working on live sewers, you've got hazards of sewage, sewer gases, disease, etc to contend with. Any attempt to work within an existing chamber will require Confined Space training and appropriate Safety Gear.

Throw in the hazards of buried services, (which are often not accurately marked out on drawings), and it can soon get complicated, and expensive if you hit something....

 

[thomp1983]

ok, had the cover off IC 2 today,

one option is to dig outside the IC and then drill into it and reroute the pipe roughly following the red lines and then follow the blue route as planned, this would require blocking the neighbours pipes for awhile but given we've all got the same 1.4m deep IC's I can't imagine it would be an issue for a short period.

My second option is as follows,

new IC where the purple square is, nicely sweep the pipes from the east and south in, then sweep out from IC round the corner and along the fence line to IC 1, this is probably my favoured option due to being able to build the IC and run all the new pipework without having to touch the existing sewer up until the point I cut the 2 pipes to run into the new IC.

I've read severn trents rules regards the IC, it has to be either sectional concrete or brick built as it's over 1m deep and must be 1040mm by 675mm and a minimum depth from top of pipe to ground of 0.9m, I'll be deeper than this due to the depth of the current pipes.

thanks
Chris

 

[Hugh Jaleak]

Don't over complicate things. Option 2 is unlikely to be accepted by ST, for the simple reason you're putting bends in both existing runs from the neighbours, some distance outside the proposed chamber. You will still then need a chamber at point 4, to turn the drain 90°.

Cutting in a new outlet from the existing chamber, ok in theory, but have you got enough room to physically get into that chamber, and install the required new channel, and make good the benching? I certainly wouldn't want to be squashed in there, bent double, trying to bench it, especially at that depth.

In all honestly, I would be looking to get the new pipework laid, between the 2 points first, then do the final connections over the course of a day. ST may allow you to use a suitable sized plastic chamber base, set into a concrete base of the appropriate size, before constructing the chamber from suitably sized concrete sections. This has the advantage of being easier to connect up, as flow can quickly be restored through the new chamber base, allowing the remainder of the chamber to be built and benched without impeding the flow.