Building limitations around retaining walls

[DanArnold]

Hello - help would be greatly appriciated

What I have been asked to do: Find out about the building limitations around retaining walls. I am trying to find specifications on how close to a retaining wall you can build structures, though is still in accordance to Standards, and so far am having no luck. So i have come here to ask around and see if anyone has any idea or can point me in the right direction to help me solve the problem.

I have attached an image which shows the retaining walls at the site. The idea is to build a set of stairs that follow the slope down the hill, that is in accordance to Australian Standards. I have found relevant information on everything else, though I have found nothing on the retaining walls and how close you can build.

I know this is an American forum, though if you can relate any information to Australian Standards that would be great, if not, no worries.

Note: Not sure if this is in the right section of the forum.
Cheers.

 

[msquared48]

I'm in the states, but, in general, if a 45 degree line from the bottom of the house footing does not intersect the wall, there should be no problem. I would probably feel safe even if this line hit as much as a foot or two above the retaining wall footing, if present. However, any more than that, I would have to ask for guidance from a geotech.

So, you can see that the lateral setback depends on the height of the wall.

Mike McCann
MMC Engineering

 

[Ron]

DanArnold...this is an international forum. There are numerous Aussie engineers here. I'm sure one of them will weigh in on this subject.

In general I agree with Mike. My guess from your photo is that you have a clayey sand material or perhaps a gravel, sand, clay mix. My point is that soil conditions have a lot to do with how close you can load behind a retaining wall. A retaining wall can be designed for any load condition...in your case, you're stuck with what you have. Further, your retaining wall is not a substantial structural wall. Most of the stability appears to come from the soil.

Get a geotech involved, then a structural.

 

[hokie66]

The type "retaining wall" shown in your picture is actually just slope stabilisation. These walls are built without footings, and they tend to move around a bit. That is the main reason they lean back so much, maintaining a lean in the right direction even after substantial movement. The blocks and the mass of earth work in a similar manner to a gravity retaining wall.

If you are just planning to build a set of landscaping steps down that slope between the walls, I wouldn't worry about the effect the steps would have on the walls.

 

[DanArnold]

thanks for the feedback / advice fellas

 

[InDepth]

It sounds like a staircase won't be a big issue in terms of surcharging the retaining wall. It would be easy to get an engineer to verify the effects of the surcharge load of the staircase. If you don't want to deal with the surcharge, you could always set the staircase on embedded posts/piles that are sleeved past the influence zone (1:1 typ like mentioned above) of the retaining wall. If embedded deep enough and designed properly, your staircase shouldn't be affected by soil movement. A wood staircase would look nice here, but I'm not sure about your aussie termites appetite.

If you are looking for a slab on grade staircase, the load shouldn't be substantial, but expect some cracking due to long term movement of soil behind retaining wall.

 

[DanArnold]

just wondering if you know of anywhere i can reference and refer to the information you have given me. Thanks