Retaining wall: have I done the right thing?

**ormeau** · 11th May 2008, 11:57 AM

I was wondering if some of the smart folk here could give me some advice regarding a retaining wall I have recently done.

After my house was built about 9 months ago, I was left with a half-metre drop down the left hand side where a retaining wall had been built to create a level house pad (see before.gif pic attached). My wife and I were worried about it being a hazard for kids (one in the oven at the moment) falling down there when playing in the yard, as well as it making side access difficult.

So after lots of head scratching I came up with the idea of making a retaining wall along the fence line and then filling it in to bring the level up to the house. With the existing rock wall retaining the house pad, I thought there would be bugger all weight to be held back in that gap.

So, I built the wall (15m long) with concrete sleepers and posts (concreted in), filled it all in (with agg pipe, gravel, geo-fabric, etc) and all was good. ( see after.gif pic attached)

Now my neighbour (nice guy) has expressed his concern about long term side affects (my new wall is effectively supported by his existing timber retaining wall) and the fact that I have basically created a wall over 1m high. I never thought of it that way - I was looking at how high I was building it above my original block level, which is about 700mm.

Now I'm worried that I've done the wrong thing by building the wall. I want to do the right thing for the sake of the two properties as well as good neighbourly relations.

So I've got three options:

After obtaining appropriate positive advice, leave the wall as is.
Dig it all up and live with the drop.
Dig it all up, take down the fence, extend timber wall up to height I require (with engineering approval) and then fill in again (an option suggested by the nieghbour in hindsight)

Any thoughts would be much appreciated.

**Terrian** · 11th May 2008, 02:46 PM

The concrete uprights you put in for your wall, how deep did you go with them ?
How far into the ground do the uprights for the timber wall go, are they wood or steel?

**ormeau** · 11th May 2008, 04:46 PM

Originally Posted by Terrian

The concrete uprights you put in for your wall, how deep did you go with them ?
How far into the ground do the uprights for the timber wall go, are they wood or steel?

Hi Terrian,

Thanks for your reply.

The nieghbour's sleeper wall has timber posts. As the wall is 600mm high, I would imagine its that much into the ground as well, giving 1:1 ratio.

My concrete wall only goes as deep as shown in the drawing - down to about the level of the neighbours yard (so about 500mm). I wanted to go deeper but hit rock and couldn't go any deeper with the small auger I hired, and it was the only thing that would fit in the limited access.

**Dan574** · 11th May 2008, 08:43 PM

what soil did you use to fill it, does it drain well?

If it drains ok and the drains are set up ok, id leave it and just keep an eye on it. if it starts pushing up against the fence then it may be time to have a good look at pulling it down.

its not holding much up at only 500mm wide.

**ormeau** · 11th May 2008, 09:03 PM

Originally Posted by Dan574

what soil did you use to fill it, does it drain well?

If it drains ok and the drains are set up ok, id leave it and just keep an eye on it. if it starts pushing up against the fence then it may be time to have a good look at pulling it down.

its not holding much up at only 500mm wide.

Hi Dan,

I filled it with sandy loam, so I expect it to drain well. I did put agg pipe down before backfilling so the water has somewhere to go.

**joe greiner** · 12th May 2008, 01:45 AM

From the timing you stated, I'd guess the neighbour's retaining wall predates the construction of your house pad. The proportions of the original cross section suggest that your house pad may be loading his retaining wall, even with the air gap above the original ground. Whoever built the bush rock wall may, or may not, have considered this. Your backfilled wall provides additional load on his wall, and distress may be expected.

The simplest fix that comes to mind is to place tiebacks about 2 metres long for each of your posts, so that the weight of your house pinches their anchor points. The tiebacks could be located between the two courses of bush rock, with an upper rock excavated and replaced over the tieback. You'll also need to make access holes in the neighbour's fence at your post locations to drill for the tiebacks.

I suggest you engage a local Civil or Soils engineer to provide specific guidance.

Joe

**Terrian** · 12th May 2008, 09:16 PM

Originally Posted by ormeau

Hi Terrian,

Thanks for your reply.

The nieghbour's sleeper wall has timber posts. As the wall is 600mm high, I would imagine its that much into the ground as well, giving 1:1 ratio.

My concrete wall only goes as deep as shown in the drawing - down to about the level of the neighbours yard (so about 500mm). I wanted to go deeper but hit rock and couldn't go any deeper with the small auger I hired, and it was the only thing that would fit in the limited access.

I would suggest then that his posts are well into the rock, if thats the case then it is unlikely that your wall will will be too much of a problem. I would be inclined to 'suck it and see', ie: give it a season and keep an eye on things, especially after rain, you haven't added too much in the way of weight, so it is quite possible that all will be fine.

If there looks like there is any movement, you will have to pull it all out, sink your holes another 500mm (into the rock) and start again.

Joe's suggestion for tie backs is also an option (I would sink 700mm x 250mm holes, fill with concrete as the tie back point, but thats just me)

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