How fix erosion under house?

[Janet_D]

Hi Workshop crew,
I’m dealing with erosion under my house and would really appreciate advice from anyone who’s tackled similar terrain or structural challenges.

The issue is beside a central pillar — the other side was treated with Shotcrete and drainage and has held up beautifully. Unfortunately, this side wasn’t reinforced at the time, and after two years of worsening erosion I’ve excavated the area and uncovered three key issues:

1. Waterproofing the back wall
The house wall is exposed down to the footings. I’m not planning to backfill — I want to keep a walkway between the retaining wall and the house for inspection and access. What’s the best waterproofing method or product for exposed below-ground walls in this setup?
2. Retaining the Clay with Drainage
The clay has slumped and needs to be retained. I’m looking for a solution that’s DIY-friendly but solid, with proper drainage. Access is tight under the house, so ideas that work in confined spaces would be especially helpful.
3. Rock Wall Stabilisation
There’s a natural rock face that’s part of the area that started to cave in. I’m considering installing mesh to hold it back the rest just in case it starts. Has anyone done this themselves or found a cost-effective solution that works in this type of space?

I know Shotcrete would be ideal — it’s proven itself on the other side — but it’s been hard to find someone willing to take on a job this small without a hefty price tag.

Would love any advice on waterproofing products, retaining wall systems, drainage tricks, or mesh solutions that have worked for you. Photos or links would be amazing!
Thanks in advance — keen to get this stabilised before heavy rains arrive.

 Photo 1. Before I dug it out

 

Photo 2. After being dug out.

 

Photo 3. Where I need to retain, you can also see Shotcrete retaining wall with correct drainage on other side of pillar.

Photo 4. The natural rock retaining wall.

 

Photo 5. Tight access, plus you can see Shotcrete retaining wall before the central pillar.

[JacobZ]

Hi @Janet_D,

Welcome to the Bunnings Workshop community, it is fantastic to have you with us.

Unfortunately, due to the complexity and potential for structural issues, this is well outside of my knowledge, and it wouldn't be right for me to try and offer advice on something I don't have the qualifications or experience to speak on.

To be completely honest with you, when the foundation of your home is at risk from erosion, I wouldn't consider this a D.I.Y. job. I would encourage you to speak with someone who specialises in foundation repairs or underpinning, or a structural engineer. Their advice will be much more valuable than anything we can offer.

Unfortunately, due to the tough circumstances, I can't see this kind of work being cheap.

Allow me to tag @Nailbag and @Dave-1 to see if they have any thoughts.

Jacob

[Dave-1]

Good Afternoon @Janet_D

Mmmmm I am sorry but I think this is outside the scope of a DYI job 😕 As much as I love retaining walls, underpinning and restoring the structure of the soil that is holding up your house is something only a professional should be doing. 

I have watched plenty of videos on underpinning as I am interested in it and I also want to one day excavate under my house but being able to structually support what is above while removing and then supporting to the same level that was originally there. For instance supporting the distance across the area via I beams while the clay is removed and then a concrete structure is built to support the foundation.

Dave

[Nailbag]

Hi @Janet_D 

I've only been involved in less sigificant scenarios and hardly qualified to provide sound advice other than a strong recommendation to get a domestic structural engineer involved.

Nailbag