Thread: wooden retaining wall

As you might be able to see from the photo the soil is a heavy clay however to excavate the area for the slab I needed to go down to rock. This means to put footings in for a bock retaining wall I would need to get a rock breaker back in for a number of hours to dig /chisel down any further in the rock. I have however thought about running more reinforcing along the slap and up at right angles to increase strength.Height ranges from 400 to 800 on the slopeHowever I am now considering a building a retaining wall using CCA treated pine sleepers 200 x 75, and using the new stumps (which go down a further 600mm into solid rock in a concrete footing) as supports. Obviously I need to dig out more of the soil to put in drainage and backfull but I don’t need to dig down any further. I am also looking at putting a channel drain at the top as well, lining the wall with plastic sheeting doubled over. My concerns, the spacing between the stumps means I might need to put in more posts for a timber wall, however the soil is clay / down to rock in places so I am not sure how much movement there will be. How long to the CCA sleepers rot out and I end up having to dig it all up to replace them?Another option suggested was to frame up the stumps, put in a load of reinforcing steel coming up from the slab, a few seep holes and pour concrete in and make a concrete retaining wall with a few stumps in it.

For my money timber retaining walls are usually only good for about 15 yrs. so concrete is a better option .

Even with concrete sleepers in steel RSJ's make sure the steel is heavily galvanized.

Hi Rat
That's something I did not consider for ease of application, concrete sleepers. I might see what I can dig up regarding sizes and cost.

Originally Posted by rat52

For my money timber retaining walls are usually only good for about 15 yrs. so concrete is a better option .

Even with concrete sleepers in steel RSJ's make sure the steel is heavily galvanized.

Naah - Untreated railways sleepers will last 15 years. So long as the treated pine is H4 (for permanent exposure to water or soil) and any cuts are painted with the appropriate CN solution then more like 40 - 50 years or longer.

Most products that are CCA H4 level Treated Radiata Pine, as defined by AS1604, carry a 50 year treatment warranty (conditions apply) against termite attack and fungal decay.

See: http://www.koppers.com.au/KW-CCA/default.aspx

So given how easy to work etc timber's the go. Use masks etc when sawing - treated timber dust (well any dust really) is not good for your lungs.

Originally Posted by Bloss

Naah - Untreated railways sleepers will last 15 years. So long as the treated pine is H4 (for permanent exposure to water or soil) and any cuts are painted with the appropriate CN solution then more like 40 - 50 years or longer.

Most products that are CCA H4 level Treated Radiata Pine, as defined by AS1604, carry a 50 year treatment warranty (conditions apply) against termite attack and fungal decay.

See: http://www.koppers.com.au/KW-CCA/default.aspx

So given how easy to work etc timber's the go. Use masks etc when sawing - treated timber dust (well any dust really) is not good for your lungs.

ok wood seems to be the way to go, easy, cheap and matches the timber stumps. Any idea of what the appropriate CN solution is and where to obtain.

I replied before I saw the photo and assumed the wall hight to be over 1m in which case replacing is a PITA, but at the hight of 1 sleeper go for timber behind the posts.

Bloss, I pulled som 10yr old perma pine sleepers out of the ground last month and due to the constant garden/lawn watering they were starting to rot/soften.

I have read reports where the h4 treatment has not penetrated right thru and has created structural problems.

I guess I just don't like to put dead timber in the ground if it can't be easily replaced.

Originally Posted by rat52

I replied before I saw the photo and assumed the wall hight to be over 1m in which case replacing is a PITA, but at the hight of 1 sleeper go for timber behind the posts.

Hi rat

The ground is on a slope, at the deep end it is about 800 high. Which means about 4 sleepers.

Originally Posted by rat52

I replied before I saw the photo and assumed the wall hight to be over 1m in which case replacing is a PITA, but at the hight of 1 sleeper go for timber behind the posts.

Bloss, I pulled som 10yr old perma pine sleepers out of the ground last month and due to the constant garden/lawn watering they were starting to rot/soften.

I have read reports where the h4 treatment has not penetrated right thru and has created structural problems.

I guess I just don't like to put dead timber in the ground if it can't be easily replaced.

I've struck the same, but right next to it was Koppers logs that had been in the same ground but for 25 years longer! There seem to have been quite a few fly by nighters about 10 yrs or so ago, seeling stuff that hadnt been pressure treated and calling it in ground use - clearly it was not.

For difficult to replace stuff, I'd stick to well known companies, who dont cut corners , like Boral, Koppers etc - anybody who makes pole home poles would be a good start - one of them failing just once might see the end of a company and its dodgy ways, via the legal system. BTW, the last sleepers I bought from bunnings, had cca right into the heart of the timber and were heavy as hell for it (also twisty as hell too, I might add )

The water needs to escape through the wall to relieve pressure in a big wet, so I don't think it is a good idea to put plastic sheet behind the wall as it will act as a dam.

Originally Posted by David L

The water needs to escape through the wall to relieve pressure in a big wet, so I don't think it is a good idea to put plastic sheet behind the wall as it will act as a dam.

But was about the agricultural pipe at the bottom to drain the dam so to speak and also the gravel fill above it.

All timber when left in contact with the ground tastes yummy to termites. I've seen a five year old timber retaining wall (treated sleepers) absolutely riddled with the buggers.

interesting to note the difference in opinions regarding lifespan.

Sorry I didn't realise you were going to use gravel to back fill with AG pipe

Originally Posted by pharmaboy2

I've struck the same, but right next to it was Koppers logs that had been in the same ground but for 25 years longer! There seem to have been quite a few fly by nighters about 10 yrs or so ago, seeling stuff that hadnt been pressure treated and calling it in ground use - clearly it was not.

For difficult to replace stuff, I'd stick to well known companies, who dont cut corners , like Boral, Koppers etc - anybody who makes pole home poles would be a good start - one of them failing just once might see the end of a company and its dodgy ways, via the legal system. BTW, the last sleepers I bought from bunnings, had cca right into the heart of the timber and were heavy as hell for it (also twisty as hell too, I might add )

Key is to make sure it is standards compliant. Most now are - some years ago there were some smaller producers who were just painting or dipping. Also as I said any cuts need to be painted with appropriate preservative - and that is too often ignored.

There are heavier duty grades too - such as the H6 used for wharf piers - permanently under saltwater.

For home use anything that last 15 years or more is usually sufficient as we swap houses every 7-8 years on average and do garden makeovers at a similar rate. And the more treatment is done the higher the cost - so it's a balance.

One can also use gal stirrups in concrete to get to just above ground level then posts above, but in this situation posts directly in ground look the go.

Have a look at the tech docs on the Koppers site - they have detailed guidelines and data sheets.

I ended up going with timber, I paid a dollar or two extra and obtain the sleepers from a reputable timber supplier so hopefully they are H4 treated as specified.

Any ideas regarding what is the appropriate preservative to paint on the cuts.

cheers
frank

What size ag pipe would people recommend.

I have some 100mm stuff around but it means a lot more digging to put it in, I am also going to have troubles trying to get a nice clean fall /slop on the ag pipe. We have had light rain in the last couple days however and I dont see any water buildup except for the corner where my down pipe has been removed.

Should I lay the concrete slap for the patio then put the ag pipe and sleepers on top? or should I try for the ag pipe to be below the slap level hence allowing for drainage below the slap level. The patio slap will be 75mm lower than the house slap.

In the far corner I am down to rock so have been jack hamming it up with an orzito hammer drill, the slow an painful way. From this way I will back fill probably only 100 to 150 mm behind the sleepers with gravel.

I also see the socked vs unsocked ag pipe debate rages on.