How to prevent leaking water through timber sleeper retaining wall?

[dave9]

I am considering building a garage over a space that used to house a carport.  One wall of the garage would sit on top of a timber sleeper retaining wall replacing the fence that is currently there.  The frame of the garage would be attached to the existing concrete slab. I have circled a sample of the retaining wall in the photo below.  It runs the entire length of the slab and is about 1 metre high.

My problem is that I would like the garage to be watertight, but sometimes during heavy rain, water leaks through timber sleeper retaining wall and runs over the slab.  I have been racking my mind on how to prevent this without excavating on the other side of the retaining wall as that is an established garden bed on common property.

Is there some kind of treatment or structure I could put in front of it to prevent the leak?  Or would a cutting a channel in the slab to manage the water flow be the best bet?

All ideas welcome!!!  Thanks in advance.

[Jewelleryrescue]

Hi @dave9 

I like timber sleepers but they will last at best 30 years.

To  be approved  by  councils you will need an engineering plan as it is larger than a certain cubic meterage no doubts.

I dislike the Council word but if you go to sell the house one day  you may have to demolish an un approved  garage.

regardless a   garage  needs long term support especially where water is an occasional  issue.

Might I suggest a  proper besser block  retaining wall  complete  with ag line and gravel drainage as a  guide line if an engineer thinks the same.

[dave9]

Thanks for the reply.  Unfortunately I don't think I can replace the retaining wall.  We are part of a strata group and the retaining wall is common property.  The fence that I want to replace is also common property, but I'm hoping that I can get the strata committee's approval to replace it.  I don't want to push my luck with the retaining wall though.  The retaining wall was built in the mid-90s so is already about 30 years old.  But it is still doing its job.

[EricL]

Hello @dave9 

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

In order to stop water from flowing out of your retaining wall the soil must be dug out and the retaining wall sealed from the other side. But if this is not possible your idea of cutting a channel in the slab would be the only viable solution. Putting anything in front of the retaining wall is not going to be practical as the entire retaining wall will need to be covered up.

Perhaps when you build your garage you could create a sort of masonry wall that is waterproof on the other side, but the issue will be where the water will flow out to. 

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

If you need further assistance, please let us know.

Eric