How to repair this rotting timber retaining wall?

[j3mesf1]

Hi all. I've noticed a run of horizontal sleepers in our retaining wall is rotting badly and need to be rectified quite soon. I'm not sure how this was prepared as it was done by the previous owner but we do have some water pooling in the area above which is likely the root cause. 

I'm unsure as to the best course of action to solve this. Given the rear nesting design I don't think removing and replacing the rotting sleepers is going to be possible. I've thought about installing uprights in the middle between each run and installing a second row of sleepers maybe two high in front of this, ultimately leaving the current one alone.

The existing uprights seem ok, for now. I'm likely going to install agg pipe above the wall to better drain water away and that may extend the life of existing sleepers.

Any advice is appreciated before I tackle this challenge.

 

 

[EricL]

Hello @j3mesf1 

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about your retaining wall. 

Covering the retaining wall with another retaining wall is not an ideal solution. It does not address the water ingress occurring in that spot when heavy rains fall. For a long-term repair solution, I would suggest taking the retaining wall apart and the drain behind it repaired. 

If you are not yet ready to take on this repair job, I propose putting in some 90x45 treated timber in front of the bowing sleeper top to bottom in a vertical fashion including the sleepers above it every half meter. Secure the timber by using Titan 14G x 100mm CL3 Gal Bugle Batten Screw. This will temporarily reinforce the sleeper wall for a period of time, but once the timber rots through then it will be time to repair it thoroughly. 

Let me call on our experienced members @Nailbag and @Dave-1 for their recommendations.

If you have any other questions we can help with, please let us know.

Eric

[Nailbag]

 @j3mesf1 

The easiest method to replace a retaining wall is to build another directly in front, while the soil behind remains retained. Walls that have been built with just a 5deg backwards angle will provide more strength and less chance of tilting forward over time.

75 x 2400 treated pine sleepers will also be stronger than the existing 50mm thick ones.using Galvanised posts will also be a stronger construction over vertical sleepers, though add considerable cost.

The new wall should be double layer lined with black plastic stapled along the top. Once built you can remove the original top wall cap and first row of sleepers and back fill the gap.

Since the garden edge suffers from water pooling, I would recommend an Ag pipe drainage system under the surface along the garden edge and connected to the storm water to prevent the pooling. 

All of the above can be done by a landscaper should the project be overwhelming, as it would be a decent project.

Nailbag

[Dave-1]

Good Morning @j3mesf1 

Well I am actually going to suggest option 3, the one that you may not be so keen on. That is to replace teh sleepers that have rotted (And check the rest of the low sleepers in that bed) Your Garden bed looks solid with no bowing other then that rotted piece. A bit of maintenece may save headaches further down the track.

The amount of effort you will have to go to to either install a new frame in front of a temporary fix may as well be put towards teh repair of the bed. The uprights are ok for now so if you leave tehm then the potyential that the rot will spread is high.

The palms you have in the bed are clumping roots and should be able to stand up to the boards being removed without too much strain on them. If you do go down the route of replacing sections of the bed (I actually think it will be the easiest but then I like digging ) I would install drainage at the bottom of the bed against the wall and also have somewhere excess water can actually drain to.

Dave

[j3mesf1]

Thanks everyone, this place is a gold mine for excellent feedback and advice I really appreciate it.

@Dave-1 I feel your idea is the one I will humour first as it's going to the least expensive option and one I can get a feel for without having to go all in.  My main unknown is if it has been correctly backfilled with gravel originally if that will pour out and make the replacement process an issue.

If I can remove a run at a time and drop in replacements then it's a big win.

Unfortunately there's not enough room to build another wall in front of this existing one (the pathway of the wall runs along a narrow path further behind the images) so I do need a solution which keeps the wall where it currently is.

Once again much appreciate the help, I will post back with how I go to perhaps help others in future as well from any of my lessons learned the hard way...

[Dave-1]

Morning @j3mesf1 

Feel your concern over the fill pouring out, think of it as an excuse to revitalize the bed? Id start collecting a bunch of containers (Pool Chlorine sized ones) to put the "fill" in so you dont end up with a pile of dirt/gravel as you replace the sleepers. I have a pool and have over a dozen buckets I have kept and keep using to shift and store soil Ask around your neighbours if you dont have one and you could be lucky. (The plastic dosnt become brittle with time and they are very hardy plus come with a lid)

Will wait for the project I think its a good one as so many of us end up with your quandry.

Dave

[j3mesf1]

Thanks Dave.  I was going to just put a tarp down under the wall and handle it that way.  My fingers are crossed there's a layer of gravel in behind which will pour out and give me ample working space to make the task easier.

Tomorrow I will have a go.

[EricL]

Hi @j3mesf1 

Please keep us updated with your progress, we look forward to seeing your retaining wall repaired.

Eric

[Nailbag]

Hi @j3mesf1 @it’s not normal practice to backfill a retaining wall with gravel. It should be back lined with plastic and then normal soil. But it often might be a mixture of anything at the lower  parts just to cheaply fill the void. 

Your most likely going to find very compressed soil behind so hopefully not to much will spill out. This should make replacement of each sleeper easier. 

Personally I would still be positioning the ag drainage along the garden line not the sleeper wall. The idea is to prevent water reaching the wall and your garden. It’s been the excess pooling water that’s contributing to the sleeper rot.

Nailbag

[j3mesf1]

Timely post Nailbag, I just finished having a look.  Managed to get the top row off and as you say only found densely packed soil and roots behind which held its shape.  No plastic lining however.

My issue is it's now apparent they screwed all the sleepers in from the back into the uprights so i can just crowbar them up and out.  I guess it leaves me with cutting them all down the middle and prying them out which compromises the job massively.  Not sure what the next best step is.