Without getting too deep soil sciences, or suggesting a PE, I would suggest extensive reading online about retaining walls, (post here if with specific questions about something) and use the "natural angle of repose) of local sand to guide how steep the retaining wall can be. This is the "safest" way to usually determine how steep the wall can be. There are ways to go dead vertical or even overhung, but those methods are beyond the scoop, or realmes of safety to do in an online discussion.
Katya Coad wrote:Does anyone have experience with building a tire retaining wall to hold back sand? I am wondering what the angle of repose with tires needs to be specifically using sand. I have already built one in the area out in front of our house (our property is pure sand). It is at about an 70 to 80 degree angle, perhaps too steep?, and I am now noticing a crack developing the whole way along the top! I am wondering if the whole thing is going to give way. We should probably stay away from the edge, but I have planted some lavender in some of the tires which now need water... but I don't want to be perched on the wall when it gives way either! Any feedback would be very much appreciated!
I have enough experience to choke a horse...can you give more details? How tall is your wall? How are the tires attached to each other? Is the intent to stabilize the hillside or to terrace the area? If you have a picture to post or send I could give you all the assistance you will need.
I would have to ask how tightly you packed those tires with sand? Did you sledge hammer them nice and tight like they do building earthships or did you just fill them full of sand and set them there? I would say the tighter you pack them, the better off you will be. I think when they build the earthships they step each row back only about and inch.
Katya Coad wrote:Yes, I think they are going to be fine. I didn't sledge them, but I did pack them fairly tightly and stomped on the sand as I lay it in, tucking it in around the edges too. I've since piled some heavy boulders on top to create a rock garden. Anyway, thanks for your feedback.
We had some worrying experience with earth rammed car tires for wall retention purposes. The dirt we tried to retain got very wet during heavy rain, and although all tires had carton in the bottom and a batter of around 2.5 inch per two courses (very steep), it blew out. Admitting it was too high (16 courses) and too long in the straight part (25 feet), the lesson was clear.
If you try to retain dirt below 6-7 feet, and that dirt is loose and it can get (very) wet, don't use small car tires with dirt and carton bottom. Use lorry or truck tires filled with gravel and double plastic bottom. And batter heavily, each course around 10 inch more inward than the previous.
If the ground you need to retain is stable and compacted, and you don't have a lot water issues (where no rain water will not collect behind the tires), I guess smaller tires and gravel with plastic will do too. Even a slightly steeper wall would hold.
Note, I assume that you used bigger tires at the first 3 layers or so. And that every tire is leveled and battered. (wall should be level).
This is not exact science, except that the code for tire walls has all to do with rammed earth or gravel, plastic/carton bottom in each tire, leveled and correctly battered walls. Also know that slightly bend walls are stronger.
I hope it all holds together and this helps you to decide to go with the current wall, or to redo it.