Author Topic: Retaining Wall Help  (Read 2811 times)

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Offline brickiematt

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Re: Retaining Wall Help
« Reply #25 on: January 19, 2020, 04:29:24 PM »
Thanks very much for the advice.

Just to clarify a couple of things.

The filter fabric won’t get clogged up over time with silt off the clay?

Do you ever see water running out of those ag pipes and/or outlets you have coming out the front of your wall?

If the wall isn’t sealed, meaning there are gaps in the sleepers or the blocks are not mortared, won’t the water come out the gaps way before it gets down to the ag drain?


No, no and no!!!
Any silt small enough will just run through the fabric, into.your aggregate backfill and eventually out the aggy drain.
If you have enough groundwater or rainfall to see water pouring out of the aggy drain or outlets, you're in trouble!!! You will barely notice any, if at all.
Again,  maybe a very small amount, but if done right, then no. That's why you have at least 300mm of aggregate  between the back of the wall and the soil. Water will fall down to the aggy drain before it makes it way across to the wall.
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Offline Pete79

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Retaining Wall Help
« Reply #26 on: January 19, 2020, 05:52:44 PM »
I wish I had of taken photos of the fountain of water that would come pouring out of rock retaining wall out the back of a house that we rented in Coolum a few years ago.

There was 3 spots along a 10m long wall that water would shoot out of the wall like a tap. ::)
« Last Edit: January 19, 2020, 05:54:30 PM by Pete79 »

Offline Moggy

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Re: Retaining Wall Help
« Reply #27 on: January 19, 2020, 05:57:54 PM »
That good for using against a solid wall, but would be as disastrous as my bentonite impregnated geofab near disaster if used as is in the diagram shown above, instead of ensuring free drainage, it would ensure little to none.
Trouble with that diagram is it doesn't comply with the Aus Standards for retaining walls. But in reality if the op is just doing sleepers and/or blocks/rocks then it's probably likely to get seepage anyway. The only real way to stop that would be a besser block solid filled wall that has 3 coats of waterproofing membrane & the 408 drainage cell and the use varying grades of backfill, didn't think he would be going to that much trouble.

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Offline DannyG

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Re: Retaining Wall Help
« Reply #28 on: January 19, 2020, 07:59:08 PM »
Thanks very much for the advise.

I am going to build both walls the traditional way that is being described here in regards to drainage behind them.

As for the treated pine sleeper wall, I did consider the gal posts that the sleepers slide into as I feel they are the best option. However I already have some sleepers that are twisted and bowed slightly so I want to use them by cutting them to length and using them as posts. And even though no one really see's this particular wall, we do prefer that look.
I know the posts will eventually rot away but I have a feeling we will be gone before that happens ;)



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Offline xcvator

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Re: Retaining Wall Help
« Reply #29 on: January 19, 2020, 09:41:36 PM »
Just don't forget the golden rule of thumb   >:D The posts/uprights must into the ground at least as much as out of the ground   :cheers:
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Online GBC

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Re: Retaining Wall Help
« Reply #30 on: January 20, 2020, 08:03:27 AM »
Thanks very much for the advise.

I am going to build both walls the traditional way that is being described here in regards to drainage behind them.

As for the treated pine sleeper wall, I did consider the gal posts that the sleepers slide into as I feel they are the best option. However I already have some sleepers that are twisted and bowed slightly so I want to use them by cutting them to length and using them as posts. And even though no one really see's this particular wall, we do prefer that look.
I know the posts will eventually rot away but I have a feeling we will be gone before that happens ;)
1200mm centres for pine posts.

Offline Beachman

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Re: Retaining Wall Help
« Reply #31 on: January 20, 2020, 08:58:24 AM »
We live on the side of a hill so we dug into the hill mean making the ground level usable. This means the back and both sides of the house have a retaining wall with the highest point being 3.2m and gradually steps down following the contour of the land. it's a block wall and for a wall of this height it needed huge foundations, bottom 5 rows of blocks are 300 series blocks and after that are 200 series blocks. Can't remember the size but the high sections have extra thick steel in every block hole and anything below 2m just had the normal steel dropped down every hole.

Then a pump and 3 trucks of concrete to core fill the wall. After that we put 2 coats of waterproofing membrane on the back, just normal agg pipe of the bottom and while the engineer said I could back fill the 1st metre with recycled concrete and then use some sort of coal ash for the balance to save money, I opted for 60T of recycled concrete and backfilled to half a metre from the top all around. For the extra $400 it saves spending tens of thousands fixing it is 20 or 30 years time.

Seeing this wall is off the house by a metre it doesn't have to be 100% waterproof, so I drilled a couple of holes about a 800mm from the bottom as an extra pressure release measure. While I've only seen these holes in action twice, it has meant there was a lot of water sitting behind the wall judging by how it was squirting out.

After a lot of rain like Brisbane is currently receiving, my wall will weep water down to the drain for about a week.

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Re: Retaining Wall Help
« Reply #32 on: January 20, 2020, 04:43:49 PM »
No issues with it? We’ve had engineers specs which specifically prohibit recycled concrete backfill. There are issues with high alkalinity, fines, and it compacts well - good for roadbase, not so good for drainage. I have 30t of it in my backyard and have had no issues with it in 10 years. I love the stuff.

Offline Beachman

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Re: Retaining Wall Help
« Reply #33 on: January 21, 2020, 08:17:28 AM »
9 years on and no problems so far as it drains really well. Only down side is the grass on top dries out very fast is summer due to lack of moisture.

Good chance the rules have changed in since building the wall, but I have a certificate from the engineer signing it off. Also the excavator driver who carried it behind the wall said he has put thousands of tons of this stuff behind retaining walls over the years.   

But I do remember the builder saying when you put as much backfill (gravel or recycled concrete) behind a wall like we did (1 metre wide up to 3M high) it takes the sideways pressure off the wall but instead makes downwards weight, but this weight helps stop any movement of the foundations.
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Re: Retaining Wall Help
« Reply #34 on: January 21, 2020, 08:56:12 AM »
9 years on and no problems so far as it drains really well. Only down side is the grass on top dries out very fast is summer due to lack of moisture.

Good chance the rules have changed in since building the wall, but I have a certificate from the engineer signing it off. Also the excavator driver who carried it behind the wall said he has put thousands of tons of this stuff behind retaining walls over the years.   

But I do remember the builder saying when you put as much backfill (gravel or recycled concrete) behind a wall like we did (1 metre wide up to 3M high) it takes the sideways pressure off the wall but instead makes downwards weight, but this weight helps stop any movement of the foundations.

A lot has to do with how they recycle it too I think. They wash and open grade it now so not much fines mixed in. The early stuff we used to get from pinkenba was like it was rolled in toothpaste. That is the nasty gear apparently.

Offline DannyG

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Re: Retaining Wall Help
« Reply #35 on: February 04, 2020, 12:05:23 PM »
One wall down and now the larger one to go.

The next one is going to built using normal retain wall blocks. It is 25 mtrs long and will be around 800-1000mm high as it turns out.

I have a really out there question to see what you blokes reckon............how would you go using plastic drink bottles as drainage fill behind a retaining wall?? They last 100's of years, they are light, they fill out quickly and easily?? What are your thoughts?

The reason I ask is because the next larger wall will require a massive amount of back fill. Due to some large rocks being in the way and the excavator bloke already digging out the area I will require around 25 cubic mtrs of fill. And I dont want to wheel barrow 3 truck loads of gravel nor do I really want to use a machine and chop up all my lawn if I can help it lol

Here are some pics of the smaller hidden wall I just did behind the shed.
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Offline #jonesy

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Re: Retaining Wall Help
« Reply #36 on: February 04, 2020, 02:49:40 PM »
One wall I replaced had plastic plant pots, coke cans and the odd stubby and general rubbish.

Another on at my place had strips of rubber that looked like they were the cuttings from truck tyre retreads. Seemed okay but we're a pain in the a... to clean up afterwards.

Bottles might not drain too well and might hold puddles of stagnant water.

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Offline DannyG

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Re: Retaining Wall Help
« Reply #37 on: February 05, 2020, 10:53:29 AM »
Thanks Im thinking some polystyrene waffles or something like that to bulk it out a little might work.  >:D
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Offline tryagain

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Re: Retaining Wall Help
« Reply #38 on: February 05, 2020, 11:18:27 AM »
I wouldn't use bottles, I think you would have ongoing settlement issues as everything settles a bit, a bottle could easily be punctured, leading to further settlement leading to more bottles being punctured which could just keep on happening. 

Offline Beachman

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Re: Retaining Wall Help
« Reply #39 on: February 05, 2020, 12:46:04 PM »
When I was a brickies labourer 30+ years ago it was common practice to hide stubbies, rum cans and basically all our lunch rubbish behind retaining walls. 
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Offline glenm64

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Re: Retaining Wall Help
« Reply #40 on: February 05, 2020, 02:20:31 PM »
You must have built my house

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Offline brickiematt

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Re: Retaining Wall Help
« Reply #41 on: February 06, 2020, 04:08:29 AM »
When I was a brickies labourer 30+ years ago it was common practice to hide stubbies, rum cans and basically all our lunch rubbish behind retaining walls.

It still is...... ;D ;D
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Online GBC

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Re: Retaining Wall Help
« Reply #42 on: February 06, 2020, 06:33:44 AM »
I hope I’m wrong but see my first post. Once loaded up the sleepers will bow.

Offline DannyG

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Re: Retaining Wall Help
« Reply #43 on: February 06, 2020, 09:13:44 AM »
I hope I’m wrong but see my first post. Once loaded up the sleepers will bow.

I did take on board your advice, in fact I had already been told that 1500 post spacings would be ideal but unfortunately due to rock in the ground this was just not possible in this instance. So 1800 it had to be.

Theres no load behind that sleeper wall. Well theres several 100 tonne of very large rocks but they have been there for 1000's of years and I dont think they will be moving towards the wall soon. The only load behind it is the drainage rock and its in place.

And the sleepers were purchased from Bunnings, they are all already twisted and bowed so a bit more wont bother me ;D

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