Decommissioning a manhole

[nickjb]

I've got a manhole where my new kitchen is going. It's where the current kitchen drains join the main soil pipe. The kitchen plumbing is moving into the extension and I'm putting in a new manhole outside the footprint. The old manhole is now not required and will be buried under the new floor

I've had a chat with BCO and he suggested putting a half section of pipe in the bottom of the manhole to make a closed pipe. What would the method be? Mortar to hold it in place then a bit of pea shingle then fill the manhole with hardcore?

 

[dann09]

1. can you scan and post a plan of the existing and proposed drainage?

2. Abandoned drainage lines are typically filled with a semi-dry mix of 4:1. Manholes may be part -filled with rubble, and 6" to 12" topped-off with the 4:1 mix.

3. Carefully work everything out before switching the drainage, all new work must be ready, esp. if a wc is involved.

4. i dont understand your/bco proposal. Dont attempt half hearted measures, or rats will possibly find a way through.

 

[nickjb]

The current gulley that feeds into the existing manhole is going. The main pipe through the manhole is staying but will be buried under the floor. A new manhole will be about 2m further downstream where the new gulley will feed in. Hope this makes sense

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• nickjb
• 6 Dec 2012
• 1

BCO is suggesting capping the over the invert in the manhole to effectively make it a tube.

 

[dann09]

1. Have a shufti at this site: pavingexpert.com/drain15
"inserting an IC into an existing line."
Scroll down to cutting pipe and making the connections.

2. I say the above, because you might be best advised to open the existing IC base, and drop-in a length of pipe. That way no come backs or blockages.

3. pack the abandoned line with semi-dry, as above.

4. what do you mean by a "sub-stack"? does it vent to terminate above, say a flat roof, or is it AAV?

5. I presume that the line from the utility room to the WC conn. is AAV vented, say in the utility room?

6. How is the WC discharging - at right angles?

7. before any work whatsoever takes place, take care of any roof issues above the proposition. Any guttering and RWP issues ( remember that the gulleys will now be re-located). Painting or replacing the fascia. Any pointing or window frame issues.

 

[Hugh Jaleak]

I'd go with suggestion 2 above, break out old chamber completely and graft a new section of pipe in its place, using proper connectors. Bodgejobs on a foul line run the risk of causing repeated blockages, you dont want it coming back to haunt you once it's buried under the new floor.