Sewage Tank Pipework

islanderre

Hello All,

So I had to replace a section of sewage line as it have gone from Round to Oval in two separate places as it was lying on timber blocks which I presume were put in 12 years ago to get the correct levels. I've removed these timber blocks now.
I’m amazed it had gone oval in these two places as it’s only a tractor lawnmower that goes over it….. To the best of my knowledge; nothing else had driven over it.

From the pics it may be seen the pipe has a slight fall towards the sewage tank until close to the AJ where the fall becomes more.
I think the AJ is sitting slightly too low as approx. 2 inches of water needs to form in the AJ before it flows into the sewage tank.
What I’d like to know is:
• Should I lift out the AJ and get the levels better or is ~ 2 inches of water okay here?
• Should I backfill the pipe in sand and then soil?

Any info / guidance would be much appreciated.

Thanks.

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salamiii

gradients

https://www.wyre.gov.uk/info/200316/building_control/166/basic_guide_to_calculating_falls_and_gradients_for_drainage

islanderre

salamiii wrote: »

gradients

https://www.wyre.gov.uk/info/200316/building_control/166/basic_guide_to_calculating_falls_and_gradients_for_drainage

Thanks for that Salamiii....
I'll study that document tomorrow....

islanderre

Dug out around the AJ this morning..... found the AJ is unsupported which is some of the problem.

So; I'm going to focus on supporting the AJ / having the fall from it to the sewage tank correct and then focus on the correct fall of the pipe into the AJ.

Should I back fill on top of the pipe with sand?

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Wildly Boaring

Sand is a poor material for under pipes or AJs
When it gets wet it gives.

The ideal material is a shingle, pebble or crushed rock (pipe bedding). For a pipe that size 10mm down.
Concrete is also a good material.

In a garden with no loading you could backfill over with soil (remove any large stones or organics)

islanderre

Thanks for that Wildly Boaring,

For the AJ; I will place a concrete block under it to give it proper support......
From the photo above; there is a block under the AJ..... but the 3 & 1/2 inch gap needs taking up so another block I'll use.
I'll chisel a groove as required into the block for the AJ to sit proper.

No traffic will be on the pipe...... Only the tractor mower goes on the lawn in the summer so I'll screen the soil as I back fill so.

Will update again once I get further on.

islanderre

So got sorted.

Got 2 half blocks and cut slots into each to match the levels needed each end of the AJ.....
Also discovered the AJ extension is missing its O Ring so have to sort that tomorrow.

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islanderre

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Put the water hose into one of the manholes and happy with how the water / waste is flowing now.... only a 1mm to 2mm of standing water now present in the AJ.

Tomorrow will hopefully sort out the missing O ring on the AJ extension and also start to back fill nice and gently with the soil..... I'll screen out any stones.

Fingers crossed that's the end of it!!!

Thanks to all who inputted.