Building a timber retaining wall need help!

Hi all,

I'm about to start building a retaining wall because This property i've purchased has massive flooding issues from the run off water of the backyard. the property has a decent slope towards the front.



^ this is the water gushing down the hill when it rained last. and then flooding the laundry area. this is a severe water issue which i'm now fixing by building a retaining wall.



I've gotten rid of the deck (incorrect installation to begin with).

My question is, Because there is so much water. Which timber should i use? Treated hardwood or treated pine? I've been told hardwood is stronger (no brainer) but when it's treated it only goes on 1-2mm on the timber where as the pine it goes in a lot further i assume 10-50%.

does anyone have experience with this?

Cheers, Elives

 

Not sure on your question about wood.. but are you going to be doing drainage as well?

Would be a good idea to dig some trenches and put in some pvc pipework to capture the water up above where you're building the retaining walls, and redirect most of the water past the house to the front through the piping (or into stormwarer if you can).

 

+1 for drainage.

How high of a retaining wall are you planning? Or are you going to terrace it?

Have you thought about concrete sleepers that look like timber?

 

yea the retaining wall will have a waterproof membrane and 100mm slotted pvc pipe with gravel n geo mesh stuff.

 

The best construction would be a besser block wall. but i'm trying to do it cheap so i've gone the timber route. the retaining wall will be 0.8m high the posts will go down 1m into the ground.

Cheers, Elives

 

Not sure about which wood, but that in itself confirms that i would have to ask why use wood where you have water issues ? I appreciate cost but I'm of the opinion with drainage you do it right or you will be doing it again..

Have you costed out other options ?

 

the side access to the property is 1050mm so i cannot get a excavator in for the foundation for a besser block wall. i believe that as long as the drainage is done right the wall will last the normal 10-20 years. to do besser blocks would be at least 3x the price. and take a lot longer. timber wall i can get dingo in with post digger attachment and have the post holes done in half a day.

 

You only need 900 mm for a Bobcat but need a good operator.

Why and where for the waterproof membrane? It's not going to achieve anything - you will need 25 mm course aggregate around the ag drain and geotex fabric over the top. More aggregate over the top.

Plenty of online resources for the design of retaining walls. Koppers have a design manual iirc.

 

Hi Scott,

i'll have the waterproofing membrane on the back off the wall and under it. to help protect the timber. why would this not achieve anything the point of it is to seal the back of the timbers so they don't get any moisture from the water. :s

yea i've figured out how i'm going to do it only thing left is just trying to decide weather to go treade pine or treated hardwood. most forums / online stuff i've searched has come back 50/50

 

You'll still get moisture through the end grain. I have a few garden beds made of sleepers - moisture doesn't seem to be a problem.

 

The water has to go somewhere. Make sure you put in decent drains that channel the run-off to the stormwater drain. It is illegal to deliberately direct stormwater runoff on to a neighbouring property.

Gravel and slotted ag piping will never cope wth a torrential Queensland downpour. The water will simply run down the yard and cascade over the retaining wall like a waterfall.

Maybe consider a spoon drain running above the length of the retaining wall piped to a stormwater drain or out to the street gutter.

It would be a good idea to get expert advice on the best way to deal with the water run-off.
Marg

 

slotted drain is aggy or sub soil drain to remove the water behind the wall under the ground

retaining wall is to reduce the pitch or fall of the block
between the the back fence and the road, and to reduce the velocity of the water
the wall dosnt look like it will be very high and there are plenty of styles of landscaping retaing wall blocks you could use
- you could maybe make it two tier -


most important thing is too landscape , with the fall being away from the house and towards the road
- concentrate on your levels water will pool in the low spots
the driveway can be your friend if you have the fall

get rid of the water above ground with landscaping and spoon drains, or belowground with a stormwater system with sumps and aggy drains
- but best to have a combo of both -

if you use timber my vote is for * treated pine *

retaining wall blocks - Google Search

 

I've decided to go with hardwood h4 timber, I'm getting a dingo and was wanting to know if i should dig 300mm holes or 450mm? i am using super strength concrete 40mpa. is 450mm overkill?

Cheers, Elives

 

Depends on the size of your posts

 

should have said haha 200x75, i've decided to go with 450mm

 

50mm cover right around is sufficient for inground.

Nail some 6 mm galv spikes into the timber to stop them pulling out of the concrete.

 

I'd recommend using steel for the posts rather than timber. Will last longer, look neater and not protrude in to your narrow walkway if you have them on the face.

Tools

 

wow haha, so the council made him direct to the "front" as in to the street? surely if he's then later gone and concreted his back yard he should be made responsible for the drainage? :s