View Full Version : boulder wall help/question
06-03-2010, 11:29 AM
I am taking on my first boulder wall soon. My foreman has plenty of experience building them, but hes not the brightest on the bidding side.
The wall will consist of 18-24" granite boulders. The total width of the hill is 60ft. There is going to be a 5' wide set of stairs going down the middle. The wall will be three teers. So this is really going to be 6 different walls of about 28 feet wide. They will only be 1 boulder high. According to my product book there is appx 10sqft per ton when using 18-24" boulders. Couple of questions now, how do I figure out how many square feet each boulder is roughly.
Secondly how does my install plan sound. I ran it by my foreman and he said it seems good but I want a few other opinons. We will start at the top and work our way down. Using a mini ex dig into the hill for the first set of stones put down some 3/4" crushed agg......lay the boulders and back fill with more crushed agg then cover with dirt and just keep working our way down. Does that sound right or no?
Lastly how would I go about determining how much crushed agg I will need. Is there a formula to figure that out. Since it needs to be compacted and all
06-03-2010, 07:09 PM
forget all these formulas.
bouders are natural products. no two are the same. You can only set one boulder at a time. takes forever.
Should be priced for Time and materials........
06-03-2010, 08:52 PM
how exactly do you plan on getting the mini over the first coure of stone you set? i guess if the total reach isnt that great you can just do it from the top. but in that case you will be undermining the previous course. you should always work from the bottom up. setting boulders is a lot of trial and error. yo umay think you have the right one but soon find out it doesnt fit right. so back to the pile you go to get another one. truat me on this, start at the bottom. you also wont risk nocking over previously set stones
06-03-2010, 09:10 PM
Crushed aggregate formula is basically the same as any other cubic yardage formula. If you will be plate compacting it, probably not a bad idea to account for 10-15% extra.
General cubic yardage formula would be length x width x depth / 27
Example for setting stone for 28 foot wall that has a 3 foot wide base and needs to be 4 inches thick:
28 x 3 x .33 = 27.72
27.72 / 27 = 1 cubic yard (in this equation add a quarter yard and forget about it)
As for backfill, same formula, just account for your assumed backfill height that you would like to come up to on the final course and the width behind the wall you would like to account for. The length is fairly obvious.
(One additional note, I would avoid using any crushed agg that is very fine and heavily sharded for backfill. Generally a washed 57 stone is a good choice. Crushed aggregates are often sandy or have tons of fine particles from going through that crushing process. Thus, they fill extremely tight and in some cases can lock up tighter than concrete. Your wall won't bleed and this can have various negative effects if you have a top layer of soil above the backfill).
06-04-2010, 12:04 AM
as far as how i can start at the top, there is access on the side to get in. This is right under the driveway and there is lawn to the side that I can easily get down so starting at the top wont be an issue.
How do you go about estimating how many tons of boulders you will need?
thanks for the help i appreciate it a lot
06-04-2010, 07:07 AM
Again -- time and materials.
This is a type of job where your client either must have the boulders or alotta money.
Our client had the boulders on his property.
06-04-2010, 09:57 PM
Just be sure if you lose one it doesn't roll into the house and take out a patio slider, I saw it happen. We we next door doing a planting years back and we heard a crash next door.....OOPS. And like DVS said, T&M for boulders it the best way, you could have to reset any one or all of them 3-4-5 times before they sit just right, that takes time, time=money, so don't go in light or you'll end up paying them to put the wall in.
07-12-2010, 06:33 PM
To answer the question of how many ft^2/boulder just multiply the average face length of the boulders = (1.5+2)/2 (ft) X average thickness of boulder (ft). This gives you the average rectangular area per boulder.
Now to determine how many tons of boulders you need: Your book tells you 10 ft^2/ton boulders. Your wall length is 56 feet. Multiply this by the average thickness (ft) and divide by the 10 square ft per ton.
I'll also add my opinion on where to start. Start at the bottom. It's easier and safer.
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