Advice Needed: Hefty Retaining Wall + Garage (Photos)

[RedRaven]

Hi guys -

I've just purchased this house, and need ideas/advice on building a retaining wall to hold back the excavated dirt shown in the photos, with a view to addding a double garage (probably brick and colorbond, approx 6m wide x 6-7m deep) to the front of the house.

Its a bit of an essay, bear with me!

First photo shows the current single garage, the dirt to be retained along the left side of the house with the concrete footings already present.

I plan (and I use the term loosely) to place the new 6x7m garage in front of the existing one - the right hand bay would essentially line up with the Falcon, although if I can push the new garage to the left as much as possible, it'll help future plans to brick in the old garage and add that space to the family room/kitchen, which is a bit pokey and dark.

Not sure if I should use the retaining wall to act as the left wall of the new garage, or leave a metre or so space behind to access the wall if needed.
The new garage will probably need a little fill (40cm-ish) to have a flat floor, as the drive slopes down to the house.





Second photo (below) - from the rear of the house, looking back towards the front. I think a bit more dirt needs to come out of this area. Love how the old bbq and shed (just visible on the right) got marooned!



The exposed earth is mainly clay and decomposed granite (rocks, big rocks, and gravelly material. Although it weeps water a fair bit, the wall has stood as shown for over two years, with little erosion since the concrete footings were installed. Good.

Originally the earth lay a metre deep against the garage, which put cracks in a single brick wall which lies to the left of the Falcon in the garage. The pillars are fine though.

Although I'm not an engineer or builder, I'm a geologist, and I'm satisfied the earth isn't moving. The brick wall damage was due to surface soil movement (from what I can tell cars used to be parked on it).

The concrete footings are council approved (although I don't have copies of that yet, a visit to Kalamunda Shire is in order). They are in the order of 400mm deep, presumably with reinforcing bar. (?) The just-departed owners couldn't finish the project (foot the bill, har har?).

For those curious souls, the wheel belongs to my Birkin clubman - a hell of a lot of fun to drive. www.birkin.com.au

Ideas, suggestions, doable? Lotto win required? Or am I insane.

[Terrian]

Steel posts (I beam) and sleeper or, if you will a decent amount in tatts, wall blocks.
(I suggest steel beams coz it looks like the wall would be more than about 1.5m high)

I would be having a 750mm+ space between the retaining wall and the garage

[pawnhead]

I don't know what they were planning with those footings. They should have been integrated with the wall, either by starter bars or uprights.
A vertical mass wall would need to be fairly wide at the bottom for that height, and needs good drainage behind it. A crib wall needs a bit of width as well as a bit of batter in its height.
Otherwise I reckon you'll have to dig some more footings.

[RedRaven]

At its tallest, in the first pic, the wall would be about six and a half feet high.

750mm gap should be okay - just enough to store the bins and any long timber etc - and have access to the wall incase it needs and maintenance.

I think making the retaining wall and the side of the garage part of the same wall is a bit risky, since any movement will compromise the garage structure, and also any weeping water problems would end up inside the garage too!

Since the granite rock of the hill is only a few feet down, water will need to be drained really well. With a bit of luck I'll route it back to a storage tank or soakwell.

[Terrian]

At its tallest, in the first pic, the wall would be about six and a half feet high.

engineers certificate would be needed for council approval I would think

750mm gap should be okay - just enough to store the bins and any long timber etc - and have access to the wall incase it needs and maintenance.

yep, could get a wheel barrow between wall & garage (I had to put up a wall after the neighbour excavated for his garage, about 450mm gap, tight

Since the granite rock of the hill is only a few feet down, water will need to be drained really well. With a bit of luck I'll route it back to a storage tank or soakwell.

yep, sounds like a plan. Good luck