Retaining Wall Replace/Repair

Welcome aboard Raddy.

Originally Posted by reddy

Hey guys,

I'm currently planning out the replacement of a retaining wall that runs down the narrow side of my house. There's a paved path between the house brick wall, and the existing timber retaining wall. The wall is slightly sloped with the block, and stands about 700mm high at the backyard end, and eventually slopes down to about 500mm at the front end of the block, the whole thing is redwood sleepers, mostly bowed and rotted through, especially the upright posts, I'm surprised it hasn't collapsed. My guess is the wall is as old as the house. The timber fence is 900mm from the wall, and was replaced when I bought the place about 3-4 years ago. I plan on replacing the entire wall in the same position, using C & H section steel gal posts, 2.4m 75x200 treated pine sleepers. Hopefully that paints enough of a picture, I've got a few questions:

Rapid set concrete vs concrete to set the gal posts - I haven't done much concreting before what's the best way to go here? Rapid set may not be strong enough for this task, there is an alternative type of a fast setting and very string concrete mix available at Bunnies.

Do i need 100mm gravel/concrete at the base of the post holes, or can I just set the posts at the bottom? Why is this packing needed? The gravel is placed under and around the bottom of posts to allow drainage, not sure you need this with steel posts.

The existing vertical timber posts are set right next to the paved path, I wont be using the same holes, BUT I will be setting the new gal steel posts right next to the paver's, along the same line as the old ones.
As I've read you're supposed to centre your posts in the holes, should i remove the paver's (this is easy enough) around the hole to allow me to centre the post, and properly concrete it in place, rather than concreting posts in on the edge of each hole, only covering 3 sides of the post? Yes you must centre the posts in the concrete. I would be tempted to have some extra width on the path side of the post.

How high up do i fill it with concrete? Just above ground level with a fall to shed water away from the steel. I would be looking at the post size and adding 50 to 75mm to the edge of the post.

Thanks in advance for any advice.

Good luck and fair winds.

Originally Posted by reddy

Hey guys,

Im currently planning out the replacement of a retaining wall that runs down the narrow side of my house. There's a paved path between the house brick wall, and the existing timber retaining wall. The wall is slightly sloped with the block, and stands about 700mm high at the backyard end, and eventually slopes down to about 500mm at the front end of the block, the whole thing is redwood sleepers, mostly bowed and rotted through, especially the upright posts, I'm surprised it hasn't collapsed. My guess is the wall is as old as the house. The timber fence is 900mm from the wall, and was replaced when I bought the place about 3-4 years ago. I plan on replacing the entire wall in the same position, using C & H section steel gal posts, 2.4m 75x200 treated pine sleepers. Hopefully that paints enough of a picture, I've got a few questions:

Rapid set concrete vs concrete to set the gal posts - I haven't done much concreting before what's the best way to go here?

Do i need 100mm gravel/concrete at the base of the post holes, or can I just set the posts at the bottom? Why is this packing needed?

The existing vertical timber posts are set right next to the paved path, I wont be using the same holes, BUT I will be setting the new gal steel posts right next to the pavers, along the same line as the old ones.

As I've read you're supposed to center your posts in the holes, should i remove the pavers (this is easy enough) around the hole to allow me to center the post, and properly concrete it in place, rather than concreting posts in on the edge of each hole, only covering 3 sides of the post?

What is the ideal hole diameter, and how high up do i fill it with concrete?

Thanks in advance for any advice.

A picture would help a lot ... but anyway ... from what I can gather, you want to replace a wooden retaining wall 700/500. You say the fence is about 900 from the wall ... is this from the retaining wall or the house wall? If it is 900 from the retaining wall then you have plenty of room to play and I wouldn't use TP nor galvanised post unless you enjoy building retaining walls every 8 years or so.

My choice would be retaining wall blocks. No mortar, no concrete. Just dig a shallow trench fill with road-base, level and set your first row, then just stack them up. Will be there when your grandkids have a family reunion for their 50 year anniversary.

Keystone®

I should get a commission from Boral

Originally Posted by havabeer

so with out being attached to a footing, what stops these from falling over?

Gravity mainly, also the geometry of the block that is very deep and the keys that slide in the holes and lock all the rows together. This system is well proven and used in public works several meters high even when in this situations the back fill is consolidated by gabions. For your case, it is an easy and very solid solution.
You also have the alternative of stepping back each row by using the back hole for the pins, but for 700mm high I wouldn't bother.

Can adept hands of engineers produce a speedy solution to a malady?


A hum ... why not?

With a building on one side and on a slope you could install a sleeper retaining wall but it will fail due to the exposure to permanent moisture.

A block wall with no cement joints will have stains all over it from water passing through and it can not be waterproofed if it likely to have any movement.

So, if you want a clean and dry wall that may well outlast the home then you need a proper retaining wall that includes a footing, a drainage system and waterproofing.

Not cheap, not fast to construct. But will last for many many years without any problems and no maintenance at all.

Good luck and fair winds.