How to fix timber sleeper retaining wall suddenly leaning?

[Ben2065]

Hi all,

With all the intense rainfall and heavy winds ins Sydney over the past week the timber sleeper retaining wall in my front yard has suddenly started leaning over. A few points

- Wall was built aprox 16 years ago before I purchased so not involved in how it was built (photo with no hedge shows just around time it was built - retaining wall and picket fence installed at same time

- I am concerned the base of some of the green picket fence posts are fairly rotten at ground level (they are in large diameter concrete footings

- I wish to stabilise the wall but not after perfection

Plan:

1 - I plan to remove the 3-4 sections of picket fence panels in the image (able to be unscrewed off the green posts) to access behind the wall to clear any debris and allow the wall to be pulled back (there is currently an air void behind the leaning wall so not completely choked with soil and debris).

2 - I plan to add additional vertical posts either timber or steel (in concrete footings) between the green posts on the exposed side of the retaining wall to provide additional bracing once wall is restored to vertical

3 - I will be aiming to leave the marraya hedge alone and undisturbed as it has taken years to establish

4 - Once the retaining wall is restored to a vertical position I was considering bolting on a very long gal box steel behind the retaining wall to strengthen the join (obvious in the photo) and avoid it bowing out in the future.

Questions:

1 - Is the weight of the timber picket fence too much force on the retaining wall once it is repositioned? Especially since the picket fence adds considerable height to the retaining wall. I could remove the picket fence and simply add a few rows of sleepers to avoid balls etc rolling off etc? It would at least allow for easier pruning of the hedge!

2 - It is unclear if the wall was pushed over due to wind, water run off or a large falling tree branch as I was not present when it occurred but it has been very gradually leaning over the last few years - would it be helpful to create some weep holes in the sleeper wall to allow water pressure from behind the wall to escape and relieve the hydostatic pressure on the retaining wall? 

Ps - the large hole in the sleeper retaining wall was to allow for an old privet tree which I removed so will also look at closing the space up as well.

Many thanks for your assistance!

[Jason]

Hi @Ben2065,

Hope the Sydney weather is calming down for you. 

Let me tag some of our most experienced contributors to the site in @Nailbag, @Jewelleryrescue and @Dave-1 to kick off the discussion with their thoughts on your plan and your questions.

Jason

[Dave-1]

Good Morning @Ben2065 

I will try and step through your questions Tho the answers arnt going to be great for saving the retaining wall.

Plan:

1 - I plan to remove the 3-4 sections of picket fence panels in the image (able to be unscrewed off the green posts) to access behind the wall to clear any debris and allow the wall to be pulled back (there is currently an air void behind the leaning wall so not completely choked with soil and debris).

A1 - Pulling back a retaining wall kind of defeats teh purpose. A retaining wall should not be able to be moved 😕 I suggest removing and starting afresh.

2 - I plan to add additional vertical posts either timber or steel (in concrete footings) between the green posts on the exposed side of the retaining wall to provide additional bracing once wall is restored to vertical

A2 - Additional posts would help always especially with a fence on top. However drainage and the way the fence is put together is a better option.

3 - I will be aiming to leave the marraya hedge alone and undisturbed as it has taken years to establish

A3 - You could try to work around leaving the hedge there while rebuilding the wall. I would suggest a transplant to somewhere out of teh way for a season while you work on the area. It tends to take longer to do then we expect and less chance of the rootball drying out.

4 - Once the retaining wall is restored to a vertical position I was considering bolting on a very long gal box steel behind the retaining wall to strengthen the join (obvious in the photo) and avoid it bowing out in the future.

A4 - The posts are the key, they have to be far enough into the ground as to not want to lean. Or you go with a different style wall depending on what look you are after. The idea of the gal box I would possibly use half way through a retaining walls lifespan to help as long as tthe wall itself hadnt picked up a lean.

Questions:

1b - Is the weight of the timber picket fence too much force on the retaining wall once it is repositioned? Especially since the picket fence adds considerable height to the retaining wall. I could remove the picket fence and simply add a few rows of sleepers to avoid balls etc rolling off etc? It would at least allow for easier pruning of the hedge!

A1b - I don think the weight of teh picket fence would be a concern if the posts are solidly into the ground and fixed. If you have someone constantly wiggling teh fence then its teh same for any fence.

2 - It is unclear if the wall was pushed over due to wind, water run off or a large falling tree branch as I was not present when it occurred but it has been very gradually leaning over the last few years - would it be helpful to create some weep holes in the sleeper wall to allow water pressure from behind the wall to escape and relieve the hydostatic pressure on the retaining wall? 

A2b - 16 years for a timber retaining wall is a fair go I would say. The way walls are built today and types of walls that people use are differant. Drainage, ground make up, height allowed, footings or piers all have changed somewhat.  The draianage/wheepholes are one way to relieve pressure but as your wall has a large lean on it already I dont think it will help correct it.

Ps - the large hole in the sleeper retaining wall was to allow for an old privet tree which I removed so will also look at closing the space up as well.

A - Privet roots are like the top part of the plant The roots themselves could have started the lean on the retaining wall.

Have a look at my profile/bookmarks for an alternative to a timber retaining wall. I really like Gabion styled walls (cages filled with rocks) These need no footings other then compacted earth, allow water to move through itself and have a long lifespan. There are a range of retaining walls that we use. Maybe dry around your area and see what people have used and note the "lean" if any on the walls. In my area a whole bunch of high side retaining walls (brick) all have that same lean. I have thought like you if the soil was removed would teh wall be able to be stood back to true vertical.. I dont think so as the same think would happen but faster as its already weakened.

Dave

[Nailbag]

Hi @Ben2065 

Sorry to see you're one of the 1,000's of victims in those big storms. I was watching the catchup TV new last night on it all and its was pretty devastating with so many massive trees over.

It's great to see @Dave-1 has already provided some pretty detailed information in his earlier post to get the ball rolling on the thought processes on solutions. 

Unfortunately the retaining wall should never have been built utilising the fence posts to secure them in place, and then support the weight of a very heavy fence. So, this is how I would tackle it, which is basically how I have repaired other failed walls.

Step 1

Remove the picket fence panels ASAP and cut the posts at the top of the sleepers to elevate the weight on the wall before it collapses. There is a good chance the posts will snap at the base where they meet the ground if you get more rain and wind.

Step 2

I would build a new one in front of the current one, providing this is possible due to your land boundary. To make the job easier, I would use 75mm sleepers of a length that have them joining offset to the current ones. This means you will be avoiding striking the old concrete footings and having to dig them out. Join the sleepers using suitably sized Jack Gal upright posts concreted into the ground. Staple heavy duty builders plastic to the back side of the wall to prevent seepage through the joins and extend the life of the sleepers.

Step 3

Position new fence posts in place behind the new wall and secure them with 12mm gal bolts, washers and nuts. I would recommend Cyprus or hardwood posts and not treated pine. You could then place something like fence palings which are cheap to roughly box out around each post about 200mm. This will keep the posts in position ready for the next step.

Step 4

Remove the top layer of the original wall and then backfill between it and the new one with soil and around the boxed out posts. Unless you want to salvage more of the older sleepers. Then fill the boxed post holes with concrete. 

Step 5

After 24hrs, you can then look to rebuild the fence.

Obviously in real life it will be a bit more work than I have made it sound, buts essentially how I would do it.

Hope that helps.

Nailbag