Extremely wet under broken gully.

2 Apr 2016
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United Kingdom
Hi there. I'm doing a DIY job on replacing a broken salt glazed gully. The gully in question has probably been broken for many years, possibly decades and the soil surrounding that area is extremely wet. The soil has a mud or wet clay consistancy. There doesn't appear to be any movement in the back of the house where the gully is located.

My main questions are:

1 - Should I be concerned about the wet ground and after fixing the gully will this still be a problem?

2 - With a new gully in place, will sub-base suffice in supporting the pipe work after replacement?

I have the pipe, gully and 110mm ceramic converter plus an angle grinder to carry out the work. See attached photos.

Many thanks in advance.

Pic of gully and back yard
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There is not much you can do about the wet soil. If you attempt to remove it, you will end up with void that needs to be filled with gravel well thumped down, but as you do this, it will sink. Providing your new pipes are self supporting, just let it be and in a couple of years a depression might form as the soil dries out. So I would not lay a solid path or concrete over this area for the time being.
You need a bottle gulley, and it should be set on a semi-dry concrete bed with a partial concrete surround.
That gulley drain leads to a manhole.
From the gulley, how far away is the manhole? Is that the manhole cover just peeping into view at the bottom of the second photo?
Now you've exposed the line why not replace all the salt glaze drainage to the manhole?
Always lay drainage on a bed of 100mm - 150mm gravel.
Thanks for the replies Frank and Vinn. This has all come about because I wanted to lay a new patio this spring and this made me discover the situation, it's looking like this year is a no-goer as far as that is concerned!

There isn't a manhole in my garden, my two neighbours do have manholes though where you might expect but this house having been owned by some bodgers has either never had one, been removed, filled in or covered over by the concrete.

So following your advice I went ahead and angle grinded the concrete away breaking the salt glaze pipe in the process, luckily not so much that I couldn't attach the converter, removed the old salt glaze hopper, angle grinded a clean cut on the pipe and fitted the new PVC gully, hopper, angle attachments and converter. Made level the hopper, filled in some holes with sand/cement and job appears to be good enough. I've put some sub-base and hardcore underneath the pipe work and rammed with a sledge hammer before installing. I will dig a well for the water to drain into and remove the water periodically when needed to aid with drying.

Do you think I can expect subsidence problems with drying? There doesn't appear to be any sign of movement at the moment.

Picture of new gully
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Thats not a bottle gulley, its a P-trap gulley and that gulley could give you problems if rodding is needed.
Is the hopper grating set at that height to be level with a new, future finished ground level?
The hopper could be higher'ed on a "Raising Piece".
At the moment the crown of your trap is almost level with the hopper grating - there is no ground cover.
The last reducer fitting is incorrectly fitted it will leak.
Large lumps of jagged concrete are not suitable bedding.
Where is the concrete bed for the gulley?
Using a bottle gulley you would have had no need for the arrangement in the photo. It would have been simpler and cheaper.
Whilst Vinn is correct in all of his points, aside from the bedding I wouldnt worry too much as its done now, especially if its only taking rainwater. The gulley looks like it might be sitting on the edge of the wall footing which would omit the need for concrete bedding but if thats not the case it really needs bedded on something to stop the same thing happening again in 10 years.

You will get very little settlement from a trench that shallow if you back fill it properly but to counteract it when doing any new drainage work on patios I always fill trenches with clean stone and then cap them with 150mm of leanmix concrete. It takes most of the settlement out of it.
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Thanks for your input. I'm convinced I need to do this again with a bottle gully to bring the whole pipe lower and in line with the original. I can get a refund on all of the items I have used as they won't be damaged.

@r896neo, you are correct that the trap is sat on the wall footing and not on the hardcore and sub-base. So can I expect settlement problems if I don't back fill the trench in a certain amount of time? Is leaving it exposed problematic and if so why? Is it to do with shrinkage of brick mortar?

Im working away this week so shall be tackling this weekend and will post the result.

Vinn in answer to your question about hopper height and relation to a new patio level, I haven't given it much thought at this stage, I've just installed at the same height as the previous.
No worries about leaving the trench exposed at all. Its more how you fill it than when. aim to surround the pipe with 100mm of 10-20mm clean stone on all sides and then cap the trenches with 100-150mm of lean concrete (5 gravel 3 sand 1 cement)
This weekend I've spent some time fixing in place the bottle gully you recommended. Here are the steps ive taken:

* Dug a lilttle further down to accomodate some sub-base.
* Installed some bricks loosely around the area that will contain sub-base.
* Applied sub-based and compacted with a sledge hammer.
* Set bottle gully in position on a bed of concrete (5 balast, 3 sand, 2 cement)
* Checked for level on the gully grate, there is a slight fall towards the pipe.
* Checked for fall on the PVC pipe, there is a slight fall away from the gully.

I would like some feedback on this before I go ahead and fill with gravel and cap with concrete.

Many thanks.

can I expect settlement problems
The way I read this 'hole' (you get it) post was that your house might collapse due to this broken drain. If that's what you where asking I don't think you have anything to worry about.
It looks like you have another waste pipe coming in from the left of your first picture so you where correct to redo the drain correctly you can almost guarantee that as soon as you started to back fill that clay to plastic converter would have popped off.
Your grate should be level as the gradient is already built in but it wont matter.
Maybe post a picture?
But if you followed the advise on here and you are happy about it they I am sure it's fine.
As tomfe said, it looks as if you have another waste pipe coming out from under your house just behind the drain cover? If this is still in use, I'd be sure to connect it up before you back fill.

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