Share
Apologies for length, I just want you to understand my plan....if I win Lotto in the next week I'll have a professional rebuild the entire wall, but currently, no money in the pot for this, but I do want to stabilise this wall.
I have a 1m high log retaining wall. The cost of having a professional to rebuild is prohibitive.
I can't rebuild the wall, even in sections, as the risk of having the ground behind collapse is untenable. There is a large concrete patio topping the wall, the house is on piers, but I really don't want to disturb this ground at all. The timbers of the wall are actually in good condition.
Underneath the large concrete patio there is a significant void between concrete and level of dirt - it has dropped fairly uniformly by around 15cm ave. Once I have repaired the retaining wall, I am having closed cell foam treatment by a professional to fill, lift and stabilise the void.
I'd love your advice guys - you always understand where I'm coming from and have offered excellent guidance. As the wall is 30yrs old, and had some 'interesting' supports added by the ex around 20yrs ago, it doesn't seem to be moving. I'm pretty sure the timber uprights he put in weren't deep enough and he attempted to rectify the lean after 10yrs by adding posts and sort of wedging-in the back of the post. The ground is awful, dirt, sandstone boulders/rocks. The wall is mostly vertical, just everso 'slightly' leaning in areas. So I'm thinking it's better to leave existing wall undisturbed, but stabilise with steel H posts, 1 m deep in ground. If you look at image 2, I've marked where I plan to add the H posts (in blue) and where I'll trim the top of the posts (in orange).
1. Where there is a slight lean, if I put an H post in vertically, there will be a gap between posts and the wall at the bottom. What should I do to stabilise at these points?
2. I'm also sure the drainage is inadaquate behind the wall (I remember some ag pipe going in). Because there's the concrete patio topping the wall, I don't have access to dig out behind it and add drainage/geotextile fabric. I'm thinking perhaps seeing if I could get some vertical drains in where I can from the top, or/and digging under the base log of wall and placing ag drains running out? (see yellow markings).
3. Any techniques to help digging post holes through flipping sandstone rocks would also be valuable - I was going to hire a petrol post hole digger, but I think it's not suited to this position and ground, and it's a case of just attacking manually.(I will be building another retaining wall 2m from this one, 55cm from patio level to comply with local Council building code for retaining walls, so there won't be a huge drop, but plan on adding planters to top for additional safety).
Apologies for giving you a right tricky one.
Morning @ezzie
No problems, ideas are just that, ideas until they come into effect. I read the thread and thought that the sandstone description would be problematic.
They do seem daunting to build i must admit but really its a slow and steady fill, surprisingly how easy they come together. Yes I do like Gabions and do promote them 
I actually built a temorary race to pour and slide the rocks down to a lower level, It worked. But now I am back to selling the cages lol So I will give some thought to a fix that may work for you.
Dave
Morning gents....just heading off to my 2nd Home (Castle Hill Bunnings) to buy up on everything required for tomorrow's big dig. (1) I understand the H steel posts just sit against the timber retaining wall, but considering the situation where those timbers are not sitting vertical, is it possible to drill some big screws through the H steel post and into the timber logs? The steel posts look so flipping thick that I'm doubting my Ozito drill will get through them. If it is possible, what type of drill bit would I require. (2) Also looking at putting some super long screws through the existing timber uprights and into the horizontal wall timbers...though I wondered if this would add stability, or actually drag the wall further out? (see photos of creative fill done by the ex). Plus, how on earth do I screw across 20+ cms of timber??? (again, see photo). Thanks again...your advice gives me the confidence to give this a crack.
Hi @ezzie,
You could absolutely drill screws through the steel posts, though ideally you'd want them positioned as straight as possible. From the looks of your setup, it seems the original logs were installed on an angle, likely because they couldn’t dig straight down. It appears wedges were added behind to pack it out. If everything's holding firm and those packers aren’t slipping, I’d lean towards leaving it alone for now—bit of an "if it ain’t broke" situation.
As for drilling through the steel posts, they are quite thick, so you’ll need a cobalt-tipped drill bit and take it slow. Running the drill too fast will just burn the bit out. If you’re using an Ozito cordless drill, post a picture of it, but you’ll have better luck with a corded 240V drill for this kind of job. Regarding the timber fixings, you can use long landscape screws to tie the uprights to the horizontals. Screws are available up to 450mm long, so getting across 20cm of timber is manageable.
Please let me know if you have any questions.
Mitchell
Ezzie...If your budget allows:
ToughBuilt Post Hole Digger (0699883)
Saxon 1500 x 22mm Hex Fencing Bar (0242144)
(The bar is 5.3kg)
Cheers
Job done! Dug 8000+ deep holes and dropped 3 x 1800 gal steel posts in. I put 2 bags of quick set cement in each post hole, mixing it well, bit by bit. Is this enough or should I add more?
Hi @ezzie,
What a huge effort—well done! Since you've already gone to the trouble of sinking them deep and doing things properly, I’d recommend finishing it off with a bit more concrete to match the solid work you've done so far.
Two bags per hole is often enough for smaller or lighter applications, but given the height of the posts and the structural support you're aiming for, adding another two bags per post would give you a much more robust footing. This will help prevent any movement over time, especially under load or in wet conditions. It’s an extra step that will make a big difference in the long-term durability of the wall.
Again, great work—it’s looking like a very solid reinforcement.
Mitchell
Afternoon @ezzie
Cheering and yeah id also put in some more concrete for sure. The hard part you have done! 
Dave
