O.P.

Hi guys & gals,

Ive spent some considerable time on the Internet researching the installation of agi pipes for drainage.
It seems there are a stack of arguments for socked vs non-socked, geotextiles, size of rock etc.

Searched this forum but also to no avail.
Please advise the best practice to install agi pipe. I will have two runs, one at the base of a retaining wall and one at the edge of a concrete path 1mtr of the house edge.

A dummies guide to installing agi drainage if you will...

Thanks in advance...

O.P.

Thanks, I have read. Im just confused as to the use of socked agi or not?
My understanding is that the:
trench is lined with a geo fabric
rock on bottom
unsocked agi on top of rock
fill with rock (what size?)
cover with fabric
in my case, no turf, continue with rock to surface level with existing turf

Have I missed anything?

Think you are basically OK.
Would only put a little rock under the agi pipe – most would be above. I use ¾ inch aggregate.
While it is more expensive, slotted pipe is preferable to the black flexible stuff (can be cleaned out without problems whereas the black flexible stuff isn’t able to cope with the methods that plumbers use to clear blockages in pipes). Easy to use normal storm water pipe and use an angle grinder to put the slots in (before it is placed in trench).
Don’t bother with the sock if you have already used geofabric to line the trench.
If you are not putting turf over the top, think of using some river pebbles/rocks over the top couple of inches for a better look (and if they are of a reasonable size then less likely to get kicked into the lawn).

1. Dig trench.

2. Lay fabric in trench, with enough fabric extra up the sides to wrap your gravel and pipe like you’d wrap a Christmas present.

3. Throw 100mm of gravel in trench.

4. Put pipe on gravel.

5. Throw more gravel on pipe so it’s covered. (Pipe should be surrounded all around by gravel)

6. Fold fabric down and wrap the gravel up.

7. Cover with dirt

mattsb writes...

Please advise the best practice to install agi pipe.

As you have discovered, there is no single best practice, just a range of opinions. I laid a lot of agi pipe in my back yard as a DIY project, heres what I learned.

Firstly, lots of people suggest that slotted PVC pipe is better because you can clean it. I would have bought it if I could fine some, I didnt want to make it myself. However when I hired the trencher and dug up my yard, everything was much muddier and less straightforward than I expected. There were all sorts of rocks and even old bricks being dug up, and basically I didnt get perfectly straight, perfectly level, clean trenches. I discovered shelves of sandstone that were closer to the surface than the 60cm trench depth. So I had wonky, muddy holes that went up and down and around rocks and stuff. There would have been no way that I could have used slotted PVC pipe, it would not have bent enough. I was very thankful for the way avi pipe was flexible and followed the curves of the trench. For the same reason, I am very glad I used socked pipe and didnt try to lay geotextile fabric separately and wrap everything. The reality is so much messier than it sounds (at least it is if you do it in winter). I had two friends help and it was a much bigger and more physical project than I expected. My whole back yard was like a swamp.

So basically, in theory there might be a difference between socked pipe, non-socked pipe, slotted PVC, geotechnical fabric and so on. In practice, if youre doing it as a DIY project then just using agi lines with a sock on it will be easier. And in my experience, so much easier that even if it wasnt technically the best solution it was the best approach for me.

Just having a trench and layers of gravel in your yard will make a difference. In a year youll have forgotten all about sock vs non-sock or what size of blue metal you used.

MumblePants writes...

Just having a trench and layers of gravel in your yard will make a difference

Yep. Just a trench filled with gravel gets you most of the way there.

John Holly writes...

Yep. Just a trench filled with gravel gets you most of the way there.

Thats all I did in my backyard with a couple of metres of pipe at the end so the water could go into the stormwater pit.

But yeah I agree with your suggested method being the best if you want the best long term results.

John Holly writes...

1. Dig trench.

2. Lay fabric in trench, with enough fabric extra up the sides to wrap your gravel and pipe like you’d wrap a Christmas present.

3. Throw 100mm of gravel in trench.

4. Put pipe on gravel.

5. Throw more gravel on pipe so it’s covered. (Pipe should be surrounded all around by gravel)

6. Fold fabric down and wrap the gravel up.

7. Cover with dirt

Other than using a special stronger ag pipe, this is more or less RMS specification and as good as it gets.

The ag pipe isnt there to carry water, its job is to create a void.

MumblePants writes...

I would have bought it if I could fine some, I didnt want to make it myself.

I made my own by drilling 10mm holes with a step bit every 50mm and laying pipe with holes to the high side and 90deg to the vertical. It works, but I cant say how well.

envy breeds hate writes...

The ag pipe isnt there to carry water, its job is to create a void.

This sums it up nicely and I suppose in that it could claim to be more useful and efficient than a rubble drain.

Ergh, I dont understand what creating a void is all about...I always thought ag pipe carried water...?

Im new to the tantalising world of DIY drainage, trying to get my head around all the detail so that when its my time to install drainage...I do it properly.

Thank you.

amberedgreen writes...

Ergh, I dont understand what creating a void is all about...I always thought ag pipe carried water...?

It’s the same thing. It’s what any pipe is. A void to carry water.

The gaps between the pieces of gravel are like small roads the water can travel along, and the agg pipe is like a central freeway connected to those roads, allowing water to escape more quickly.

And without the pipe, the void wouldnt exist...how existential....and a perfect metaphor, makes complete sense, thank you.

Water follows the path of least resistance.

in a pressurised system, say water supply, the water is forced to move along the pipe that enclose it.

Drainage is a different beast, the whole point is to allow the water a way to drain to somewhere,
the water arrives via soakage, rain, whatever
and will flow away from any place if it easier to do that than stay where it is.

So when doing drainage, always look for a way to get water to flow from one place to another.
and never try to stop it, always divert it to somewhere.

Ag pipes are not sealed as they are supposed tp allow water to flow into them
and then supply an easy exit route for water,
but they can also work in reverse if you put them in a place where they fill up,
and cannot drain water away fast enough, the water would then exit out the holes.

rock , gravel, sand provide an easy pathway for water to move from one place to another.

amberedgreen writes...

And without the pipe, the void wouldnt exist...how existential.

A rubble drain does create voids but these might more easily fill with silt. Mind you Ive never been overly swayed that something similar wouldnt also happen with Ag pipe.

Im going to go with John Hollys 7 step drainage plan. Just need to figure out how to do the sums so that Im not shovelling and wheel-barrowing more gravel 30 metres uphill from the street to the back yard than is absolutely necessary.

Show me these Stooges writes...

Mind you Ive never been overly swayed that something similar wouldnt also happen with Ag pipe.

Ive dug up a fair bit of ag pipe in my time and not as nicely set up as described on here
just laid in dirt with no sock, never seen one full of dirt yet.
I suppose it could happen, but the little amount of silt that flows into it via the tiny slits,
would be fairly easily washed away by water flow.

Avatar1 writes...

would be fairly easily washed away by water flow.

One thing ive always wondered is if anyone pays enough attention in how they lay the agi “path”, with falls, how straight it is, or in a way to minimise the ups and downs so water can actually flow. Or is that not even an issue.

Just like laying solid pipe with fall so water can flow and travel.

But i can see issues where if the agi is chucked into the trench, twisty and turny, up and down, then youll have localised problems where the bit of silt isnt being washed away as its sitting in a dip/low spot in the agi. Then over many years it builds up.

And also if theres any section of pipe, or even the trench, that is lower than the outlet drain, when it fills up, itll drain to a point where water below it wont flow up hill through the agi/trench.

I could be over thinking it, who knows.

2 Fast writes...

I could be over thinking it, who knows.

No, you’re not overthinking it. Water flows down hill, and silt settles in depressions.

Avatar1 writes...

would be fairly easily washed away by water flow.

Err, yes, although there are holes all around the pipe, so what goes in must come out

2 Fast writes...

One thing ive always wondered is if anyone pays enough attention in how they lay the agi “path”, with falls, how straight it is, or in a way to minimise the ups and downs so water can actually flow.

Definitely. When I put in some drainage, I ran a stringline 1 m above the required bottom of the trench, with exactly a 1 in 50 fall on it – then dug the bottom of the trench to exactly the right depth.

I also buried a big, heavy metal stake at the end of each trench to make them easy to find with a metal detector if I ever need to.

It’s not hard to spend a little eztra time to get these things right.

Digging up an old thread here, but have a few questions:

1) what size agi pipe to use ? I see Bunnings sell 50mm, 65mm and 90mm diameter

2) how deep to dig trench ? Will 400mm suffice ? Noting I have to run pipe about 40 metres so need enough depth to have constant fall to the low point of discharge

3) is it fine to wrap pipe and gravel in geotech and then soil/ turf over it, or would it be better to fill with gravel up to the top of the trench ?

4) planning to connect low end of drain into stormwater riser pipe that is sticking up in the middle of back yard. Is there a connector to enable this (noting connection will be under the soil level)?

Thanks all

Also digging up an old thread with some questions:

1. I understand that agi pipe collects groundwater – but how far from the trench will the water come from? Ive got an area about 5m wide that is pooling water. If I run the trench straight through the middle, will water ~2.5m away be drawn into the drain? Should I run a couple of trenches?

2. I know everything that I need to buy to do the job, except what to use to terminate the 100mm Agi Pipe at the stormwater. Any suggestions on what to buy?

3. I cant seem to find any appropriate pits on the Bunnings website (Id go look in person, but lockdown...). They all seem to have the pipe attachment at the bottom, whereas I was expecting, based on videos Ive watched, that I would attach the Agi Pipe to the side of the pit.

4. How far under grade should the top of the drain be in order for the grass above to still be able to grow decently?

Cheers.

Punchcard writes...

got an area about 5m wide that is pooling water. If I run the trench straight through the middle, will water ~2.5m away be drawn into the drain?

If there is a fall and the ag pipe is at the lowest point, it will drain. If there’s no fall then you would probably need more than 1 pipe.

2. I know everything that I need to buy to do the job, except what to use to terminate the 100mm Agi Pipe at the stormwater. Any suggestions on what to buy?

I believe you’re supposed to terminate the ag pipe into a pit, then from the pit to the stormwater. Not directly from ag pipe into stormwater.

3. I cant seem to find any appropriate pits on the Bunnings website (Id go look in person, but lockdown...). They all seem to have the pipe attachment at the bottom, whereas I was expecting, based on videos Ive watched, that I would attach the Agi Pipe to the side of the pit.

I think this is one that I’ve used before:

https://www.bunnings.com.au/everhard-easydrain-polymer-rainwater-pit-case_p4770245

They are just a ‘bucket’, you cut out what apertures you need for feeds and drains depending on your own usage.

4. How far under grade should the top of the drain be in order for the grass above to still be able to grow decently?

At least 450-500mm of total depth

Got a few waterlogged sections of the new place. Im going to run an Agi pipe along the lowest edge to wrap basically around the high-side of the house. Im just going to run a flexible pipe with sock, slightest layer of rock underneath <100mm then another 100mm on top of the pipe, itll essentially be an un-compacted rock path over the top also wrapping around the house.

Soil is very clayey, so dont need too much depth and not putting turf on top of it. Also deciding to go a bit more shallow because theres a chance I might dig it out and concrete (or similar) over a section of it, Its easier to go deeper in sections later rather than maybe have to try and lift sections.

I think the trick is to run along the low-side and try to keep a barrier between the water flows and the house.

Ive found an under-the house agi pipe which runs along some foundations and that needs replacing or re-connecting too.

Bumping an oldie...

Our backyard is a small 2m section of paving then a 6m x 2m area that is more or less a raised garden bed 20cm high. The previous owners grew a tree here and had pavers leading to a rear staircase but the whole space was overgrown, weedy and dry.

The wooden edging was completely rotten so I removed it all, cleaned everything out and put down some fresh soil to try and grow some kidney weed.

(Edit. Dang this was way longer than intended)
Two days later a thunderstorm rolls through and Im getting massive pools of water along the right side (timber edge).

https://photos.app.goo.gl/aPsGoKB8MRhQFzFA8

At the time I didnt think wed need any drainage here — there wasnt any previously and there wasnt flooding issues that we noticed (though it might explain the rotten wood...)

I added some quick aeration along the edge and it all drained away quickly but I can easily see this becoming a problem.

Will better aeration throughout the space save my butt or should I try to add some drainage along the edge? The issue being theres no convenient place to drain said water away.

This post is a couple of years old but we are doing this process as instructed by drainage experts. However, they suggested black plastic in the bottom of the trench. There hasnt been any mention in the post, so is it necessary or would it maybe add more to the drainage.

So what do you do if youre building a small retaining wall where you cant connect the agi pipe to a storm water to drain away? Thats what Ive always been confused about, I thought people just put an agi pipe behind the wall and cover with stone but didnt see the point in doing that if its not connected to an actual drain like storm water.

mattsb writes...

A dummies guide to installing agi drainage if you will...

I used to work for a Civil Contractor and I would recommend Geofabric between soil and the aggregate (say 10mm or so). This will be better than just socking the aggi line and no Geofabric as it stops the finer material from migrating to the pipe and clogging it up. Once you have installed the Geofabric then you could choose to sock the aggi line but, most of the work has already been done with the Geofabric.

Pretty much the steps John Holly suggested except, it’s it’s a retaining wall, there’s no need to cover with dirt. Leave the aggregate exposed. You don’t want the dirt touching the wall.

sugarray writes...

I would recommend Geofabric between soil and the aggregate

I just used old carpet.

Darb81 writes...

So what do you do if youre building a small retaining wall where you cant connect the agi pipe to a storm water to drain away?

John Holly writes...

Water flows down hill,

Thats the crucial bit. If theres nowhere for it to flow, it will continue to build up until it finds a way through or over your wall. There absolutely must be somewhere for the water to drain to if you want your wall to last beyond the first good rain.

Ive got a similar situation. Ive drained the retaining wall (to stop it falling down), but the pipe just ends at the side of the yard on the high-side of the house (but off to the side).

During wet periods, that part of the yard now gets really soggy and I want to finish another 10m of block retaining wall which will end in about this area. This wall is more decorative than the last one which was more structural.

Im wondering if there are any creative/innovative ways of getting water out of the soil and either deeper into the clay underneath? My wet area is 1m above the carport which is 20m of concrete which I dont want to bore under or really have to touch, but it runs from the property boundary to the edge of the house and I cant run anything above-ground either.

Im thinking of digging a few post holes about 1m deep (about 200mm diameter) in the clay a 1m spacings and filling them with rock which will essentially just become sub-surface water storage and hopefully drain away over time. Almost like a surge storage capacity in really wet periods. The down-hill part from here is through the neighbours yard – away from our yard/house.

NotEnoughTimeToThink writes...

Im wondering if there are any creative/innovative ways of getting water out of the soil

Ag pipe has to be drained, either into a surface drain (gutter?) or sub-soil drainage (stormwater) pipe. Saturated ground will break up concrete paths/driveways/foundations with wetting and drying cycles.

Darb81 writes...

So what do you do if youre building a small retaining wall where you cant connect the agi pipe to a storm water to drain away? Thats what Ive always been confused about, I thought people just put an agi pipe behind the wall and cover with stone but didnt see the point in doing that if its not connected to an actual drain like storm water.

Ok this only applies to a retaining wall. The reason you put agi pipe in is to move the water which can build up and in return reduce the pressure that is on the wall. If you dont then there is the potential for that water to move the wall.

So in this case you could just run the pipe so that it drains out the front of the wall. Of course that water is now at the base of the wall, but that is better than it sitting behind.

Also same reason you often see small pipes put in the face of masonry retaining walls.

Yeah, I definitely want to get mine out from behind the retaining wall. I just cant decide where to put it, given the LPOD is about 70m away on the other side of about 40m of hard surfaces as well.

Yeah, but it could provide maybe an extra 1000L of water. Its only during the heavy and constant rains that I notice the ground getting very wet under foot.

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