Curves in a stone wall 4

[glvsav37]

Hello all, I apologize if this is in the wrong spot, but I have a simple question for greater math minds then myself.

I am building a simple garden wall, no more then a foot and a half high. I am using a rectangular stone block 12 inches long, 4 high and 8 deep.

My problem is that there are two curves in the wall, one of an 8-9 foot radius the other of 4 foot. I want to trim the back corners of the blocks so that the edges meet clean and flush, especially on the top rows, through the turn.

Is there a formula I could use that would tell me how much to trim off each end for the given radius?

thanks in advance

glvsav37

 

[gbam]

Another possible approach would be to graphically determine the amount to trim. Get a peice of graph paper so your drawing will be to scale. Using a push pin and a pencil draw your radius and then draw to scale each block. measure the overlap and you will have your required number. Remember that you can always use grout/mortar to fill in the oopsies. When I built my garden wall, I did this in the field rather than on paper. That way i could tweak where needed. My wall has an "S" curve in it making it really interesting to build. Goodluck and have fun, also make sure you have enough masonary blades for your circular saw. I ate up 10 during my experience, having to get more once i found that it was my last one.

 

[layfieldman]

I don't know if this is what you are looking for but you would also need to find the trim as you enter and exit the curve as well so I'd just draw the entire wall length in a drafting program (AutoCAD) to scale and find it that way.

 

[aepaul]

If the graphical method seems a little too tedious, there are a couple of mathematical approximations that will help you determine the distance from the corner of the block at which you will need to start your cut.

The angle of the cut on each end of the block can be calculated by (180)(L)/C, where L is the length of the block and C is the circumference of a circle with the radius that you plan to use for the curve in the wall. So, for your 8 foot radius wall, the rotation for each block would be (180 degrees)(1')/(50.27') = 3.58 degrees.

Then, the distance from the corner of the block can be calculated using simple trigonometry. Distance from corner = D(tan a), where D is the depth of the block and a is the angle of the cut. Again, for your wall with the 8 foot radius, Distance from the corner = (8 inches)[tan(3.58 degrees)] = 0.5 inches.

Adam
Rupert Engineering, Inc
Auburn, WA

 

[digger242j]

At the risk of offering a suggestion that engineers may find abhorrent (that is to say, one that is non-mathematical, non-graphical, and not completly determined before the actual fact of construction begins)....

Why not lay every *other* block through the curved area of the wall (knowing that at the face they will be 12" apart). Once those are in place, rest another block on top, spanning the empty space. Reach underneath and use a piece of chalk to mark where to cut.

It certainly won't look as tidy as uniform angles cut at either end, but appearance shouldn't be a factor in any but the top course. The advantage is that you'll only need to make two cuts on every other block, as opposed to cutting both ends of *every* block. My calculations show that the required number of cuts will be reduced by 50%, (+/-).

Of course, once you get to the top course you're back to needing the advice of sombody with higher mathematical skills than mine.

 

[MPENN]

If the blocks are rectangular (12" x 8")and set along a 8.5' radius, the back joint is tight and the exposed joint is approx 0.0851'(1 3/16"); for the same block set along a 4.0' radius, the back joint is tight and the exposed joint is approx 0.1997' (2 3/8"); the back joint between the two radii is tight and the exposed joint is approx 0.1426' (1 11/16").


Most wall blocks for MSE type walls have a taper to the rear that enables closing up the exposed joints.

(quickly laid out in AutoCad)

 

[glvsav37]

thanks to everyone who weighed in on this!!

the wall was completed this past weekend and it went off without a hitch

for a few photos of what you helped with, go to...

http://www.keithgdesign.com/gardenwall.htm

thanks again!

kg