Thread: Advice on burying stormwater pipe

Originally Posted by Vernonv

Hi All,
I'm looking for advice/information on the best way to bury a stormwater pipe.

The pipe will be going under our driveway (gravel) and will probably be no less that 1 foot below the surface. The pipe will be going to a water tank.

We only get light vehicles on the driveway (cars and possibly a 4WD - no large trucks, etc)

What size/class pipe should I use - will normal 90mm be OK?
Should I encase the pipe in concrete - or should I just surround it in sand and then backfill?

Any and all advice appreciated.

90mm stormwater pipe is fine, but I would be going deeper than 300mm (actually, I did go deeper, 900mm, but I have a mate who has a small back hoe, here he is trying to knock down my garage (please note, custom built garage ) [ame="http://www.youtube.com/watch?v=ejAxk9PX96I"]LINK[/ame]


anyways, I would not go less than about 500mm depth for pipe that is likely to have vehicle traffic, other option would be to dig the trench 400mm deep, 350mm wide and lay 270mm concret pipe, and slide your 90mm stormwater through that, then just backfill the trench with sand, and top over with crushed rock.

I think 300mm to the top of the pipe will be fine provided the trench is kept to just clearance at the sides of the pipe because there wouldn't be much pressure on the top of the pipe. I have seen storm water pipe at less depths without any problems.

Thanks Guys.

So Barry, what your are suggesting is to only have the trench wide enough to fit the pipe?

Should I surround the pipe with sand (or similar material) before backfilling or doesn't it matter?

Terrain - my shed it coming along nicely - will be good having 7.5 x 12 of workshop space and another 3 x 12 covered area for storage (awning off shed). I should post some pics up.

Originally Posted by Vernonv

Thanks Guys.

So Barry, what your are suggesting is to only have the trench wide enough to fit the pipe?

Should I surround the pipe with sand (or similar material) before backfilling or doesn't it matter?

What Barry says is true, to a point, if the ground is very stable, ie: bloody near rock hard to dig, 1/4 minus (7mm) stone around the pipe.

Terrain - my shed it coming along nicely - will be good having 7.5 x 12 of workshop space and another 3 x 12 covered area for storage (awning off shed). I should post some pics up.

7m wide x 6m deep is my garage, 6m x 6m shed going in behind it (at some stage

Wouldn't hurt if you had some gravel or scoria to lay it in and to put over it. That's a requirement where I am with PVC sewer pipes even if they're 3m down.

I normally use 100mm sewer grade pipe, it's stronger and much more suited to rodding if it ever gets blocked.

Originally Posted by Vernonv

Thanks Guys.

So Barry, what your are suggesting is to only have the trench wide enough to fit the pipe?

Should I surround the pipe with sand (or similar material) before backfilling or doesn't it matter?

Terrain - my shed it coming along nicely - will be good having 7.5 x 12 of workshop space and another 3 x 12 covered area for storage (awning off shed). I should post some pics up.

I have stormwater pipes that are only about 2 inches under the ground that are in Granite sand that have been there for 20 years that I have driven my ride on mower as well as my Toyota Hilux over with out any damage so I would suggest using some sand around the sides and an inch on the top and refill with the natural soil dug out of the trench but dig the trench with very little clearance around the pipe.

I'd basically go just a little deeper (two foot) or put a bit of concrete over the top of it where it goes under the driveway. This is simply because, after heavy rain (remember it?) when the ground is waterlogged, a heavy vehicle can sometimes have a wheel sink down and crush them. This happend to me when my brother drove his Land Cruiser over mine.

If you can keep them well below what a vehicle's wheel would reach in a bog, you should be OK.

Thanks for the input everyone.

Rossluck - the ground where the pipe is going is pretty well compacted and we have never had any issues with it getting boggy, etc.

Thanks for clarifying that Barry - sounds like the way to go.

Bricks (I was wondering when you were going to post) - can you get fittings to go from 90mm stormwater to 100mm sewer. Also I saw somewhere that there is a heavy duty version of the 90mm stormwater - would it be any good?

Originally Posted by Vernonv

T
Bricks (I was wondering when you were going to post) - can you get fittings to go from 90mm stormwater to 100mm sewer. Also I saw somewhere that there is a heavy duty version of the 90mm stormwater - would it be any good?

pretty standard fitting, 100mm to 90mm adaptor, bunnings sell them , as would almost any place that has plumbing supplies (even your local garden supplies is likely to have them.

You can buy fittings to go from 90mm stormwater to 100 mm pvc, conveniantly it called a 90mm stormwater to 100pvc adaptor, ( not taking the mate, that's what its called).

For some reason you can get sqaure downpipe- 90 stormwater, but not to 100 pvc. But you can adapt after.

The thicker stormwater pipe i've not had anything at all to do with, I'll be honest mate i'm a stubborn git at times, and not using stormwater grade pipe is one of my quirks. So as for if it's good? I cant honestly tell you.


When you dig the trench make the trench 100 mm wider and deeper and fill with sand to 100 above the pipe. This will stop little rocks punching through the side of the pipe when you backfill. If when you dig the trench the dirt is reletively loose and fine, Not in clumps bigger than around 20mm of dirt and there arn't a noticeable amount of rocks, you could probably get a way with using the same stuff as backfill.

To work out how much backfill you need-
Length x width x height ( in meters.) x by 1.8 will give you the approximate tonnage of what you need to order.

The 100mm stormwater pipe, if you can find it seems to be ok as far as stormwater pipe goes, has a similar wall thickness to the 6" stuff. You dont see it much here in sydney but Im with Bricks as far as the 90mm rubbish goes, better off spending the extra and buying 4"sewer (DWV) pipe and fittings, it will save you in the long run.

Thanks for the additional info guys.

Ok, so I'll go for the 100mm sewer and make sure that I surround the pipe in sand (thanks for the formula Bricks).

You can change the down pipes to round Pvc Eg; 65mm for easy hook up to underground system too.