Land Drainage

[G-MART]

Good morning everyone.

Having dug an exploratory hole to expose the footings on a bungalow. I have exposed damaged or damaged while digging 2 x 12" lengths of 3" OD clay land drain...... this is obviously historic from when the bungalow was built (1960's) while the pipe was exposed the hole filled with water flowing in from both ends of the pipe. These were simply but jointed to the next pipe in the run. I have repaired this section with flexible couplings and pvc pipe (pictures below) and partially refilled the hole. It is still waterlogged and water sitting on top of the partially filled hole.

I would like some advice as to if this is to be expected until fully filled or if there is something I can do to stop this.

Any experience or advice gratefully received.

 

[Chuck]

I have repaired this section with flexible couplings and pvc pipe (pictures below) and partially refilled the hole. It is still waterlogged and water sitting on top of the partially filled hole.

Drains are not my thing but I do know that land drains are normally perforated with holes and surrounded with gravel, which is how the water is taken out of the soil and into the pipe. Also, Jubilee clips aren't going to last long if they're buried in wet ground.

Needs fixing properly using the right materials and methods IMO. Might be a good time to figure out or trace where the water in these drains is supposed to end up and check that there aren't other blockages.

 

[exedon2]

The clay pipes you have found (correctly called land tiles) were laid with a small gap then surrounded by 30mm porous infill . This could be gravel crushed limestone crushed concrete depended where you were.
Strictly speaking you should have jointed sections with a section of porous pipe then surrounded with in fill.
Maybe drill some 10mm holes in new pipe then surround with porous material.

 

[G-MART]

Drains are not my thing but I do know that land drains are normally perforated with holes and surrounded with gravel, which is how the water is taken out of the soil and into the pipe. Also, Jubilee clips aren't going to last long if they're buried in wet ground.

Needs fixing properly using the right materials and methods IMO. Might be a good time to figure out or trace where the water in these drains is supposed to end up and check that there aren't other blockages.

Hi Chuck, thank you for weighing in. As I understand it modern land drains indeed are a perforated corrugated pipe - the clay pipes here are their predecessor and the butt joints aren't sealed and do the same job as perforations on a modern system.

The existing pipework doesn't have any gravel surrounds.

I have bedded the new pipe on gravel and had hoped the solid pipe would give a path for water to flow. The couplings are for underground use with stainless clips so should be fit for purpose

I think the issue is when both ends of the clay run are open water flows from them and isn't flowing to an outlet and is taking the path of least resistance into the sump that is created by the hole.... Though it was dry while digging!

The run is parallel to the back of the house and I believe extends into the neighbouring property (which is lower and so should lead to a drain)

I can source and replace with clay pipe to match. My concern is can it be left if reinstated as it was before?

 

[G-MART]

The clay pipes you have found (correctly called land tiles) were laid with a small gap then surrounded by 30mm porous infill . This could be gravel crushed limestone crushed concrete depended where you were.
Strictly speaking you should have jointed sections with a section of porous pipe then surrounded with in fill.
Maybe drill some 10mm holes in new pipe then surround with porous material.

The clay pipes you have found (correctly called land tiles) were laid with a small gap then surrounded by 30mm porous infill . This could be gravel crushed limestone crushed concrete depended where you were.
Strictly speaking you should have jointed sections with a section of porous pipe then surrounded with in fill.
Maybe drill some 10mm holes in new pipe then surround with porous material.

Thanks Exedon2. You are right the 3" pipes are known as land tiles Its great to hear from someone familiar with them.

They are only short 12" and I have put a camera up each open end and seen the next joint. They are butted (not sealed but not with a gap) and just seem to be laid in heavy clay with no infill gravel etc.

I can source some old salvage replacements and reinstate them. However the flow of water seems to be into the hole not along the drainage run.

I assumed perhaps wrongly that losing 3 butt joints wouldn't adversely affect the system too much and any ground water would run to the next joint and then follow the channel the land tiles form and away to a drain.

They run parallel with the house back wall.

I think I will have to put a inspection camera along the run ech way and see if I can find the eventual drain point.

Do you think these would always flow to a drain or perhaps just direct water away from the housing?

 

[Ric2013]

I'm not experienced in land drainage, but remember reading about it some time ago and I think I vaguely understand your setup. Bit of a guess, mind you, so please take my thoughts as an idea to be considered critically rather than advice.

I would suspect the function of that drain is that, when the water level reaches above the drain, the pipe fills with water and can flow to wherever the outlet is and essentially reach its own level, as water does. The pipe may well have been laid to a level and probably terminates at a ditch or soakaway. If the drain has dipped a bit over time, then you may get the odd section staying partly full, but the water cannot significantly rise higher than the pipe.

Quite why the section you have exposed was full of water is a bit of a guess. Perhaps the outlet has become obstructed or someone has obstructed it and the drain was no longer funtional, the joints had largely sealed up with clay and, by digging next to it, you've just created an alternative outlet? This shouldn't really matter, as being in clay, the water won't soak anywhere far and will merely sit at that level.

By sealing the joints, and using plastic pipe you've made a watertight section that cannot allow water in or out. As the clay will take time to drain itself, the water that cannot escape through the pipe will sit for some time. Also, the very fact that you have dug a hole may result in water running in from the sides of the hole. For a 2' section, I wouldn't be that concerned to be honest - the water will just have to flow 2' either way to find the next joint.

What I would be more interested in is whether that drain drains other land than yours, whether there was originally a soakaway that has clogged up and needs renewing or if a neighbour etc has blocked the original outlet and whether an alternative outlet or soakaway could be provided somewhere at least 15' from the house. Because you don't want to be importing water from other land if there is no means of dumping this water and, if the outlet needs renewing you may be able to get whoever else benefits from that drain to contribute.

An interesting experiment might be to temporarily replace that plastic pipe with a section of plastic pipe with a large cutout at the top to see whether the pipe is full of water, or only half full of water and whether, if you pour extra water into the pipe, it rapidly runs away to somewhere, or whether it fills up the pipe and just sits there. This would give you some idea as to how that drain is currently functioning.

 

[exedon2]

I spent a fair part of my early career working on drainage schemes including land drainage.
I suspect your correct that the land drain is intended to keep ground water away from the building. I've certainly seen this done on 60s estates.
As its probably never given you any problems in past I would reinstate as near as possible to how it was.

 

[Ric2013]

I spent a fair part of my early career working on drainage schemes including land drainage.
I suspect your correct that the land drain is intended to keep ground water away from the building. I've certainly seen this done on 60s estates.
As its probably never given you any problems in past I would reinstate as near as possible to how it was.

If the OP tries to get it as close to how it was by drilling holes in the new plastic pipe, should he or she drill these holes at the bottom, the top, the side, or all around?

 

[exedon2]

The purpose made pipe has holes (actually small slits) all round

 

[G-MART]

I'm not experienced in land drainage, but remember reading about it some time ago and I think I vaguely understand your setup. Bit of a guess, mind you, so please take my thoughts as an idea to be considered critically rather than advice.

I would suspect the function of that drain is that, when the water level reaches above the drain, the pipe fills with water and can flow to wherever the outlet is and essentially reach its own level, as water does. The pipe may well have been laid to a level and probably terminates at a ditch or soakaway. If the drain has dipped a bit over time, then you may get the odd section staying partly full, but the water cannot significantly rise higher than the pipe.

Quite why the section you have exposed was full of water is a bit of a guess. Perhaps the outlet has become obstructed or someone has obstructed it and the drain was no longer funtional, the joints had largely sealed up with clay and, by digging next to it, you've just created an alternative outlet? This shouldn't really matter, as being in clay, the water won't soak anywhere far and will merely sit at that level.

By sealing the joints, and using plastic pipe you've made a watertight section that cannot allow water in or out. As the clay will take time to drain itself, the water that cannot escape through the pipe will sit for some time. Also, the very fact that you have dug a hole may result in water running in from the sides of the hole. For a 2' section, I wouldn't be that concerned to be honest - the water will just have to flow 2' either way to find the next joint.

What I would be more interested in is whether that drain drains other land than yours, whether there was originally a soakaway that has clogged up and needs renewing or if a neighbour etc has blocked the original outlet and whether an alternative outlet or soakaway could be provided somewhere at least 15' from the house. Because you don't want to be importing water from other land if there is no means of dumping this water and, if the outlet needs renewing you may be able to get whoever else benefits from that drain to contribute.

An interesting experiment might be to temporarily replace that plastic pipe with a section of plastic pipe with a large cutout at the top to see whether the pipe is full of water, or only half full of water and whether, if you pour extra water into the pipe, it rapidly runs away to somewhere, or whether it fills up the pipe and just sits there. This would give you some idea as to how that drain is currently functioning.

Hi Ric 2013 loads of great points there. Thanks a lot for your post. I think what you are saying aligns with my own thinking. I'm a little worried but not overly so. I am concerned that the outflow is blocked somewhere. I wasnt worried until I exposed it. 'Ignorance is bliss' I think I am going disconnect the repair and send a drain endoscope each way down the pipe. (Currently I dont know if the fall should be right (and it only drains the one garden - or flows left into neighbouring property) who did have works done for an extension over 10 years ago.

I will if I do a video survey post the results on here as it may interest some people.