Concave and confounding.

Our retaining wall sits between two basalt columns. By designing it to have not only a diagonal pattern (see Friday's post) but also be concave in shape, both laterally and vertically, we not only make a stronger structure, we give ourselves lots of options for tilting the granite blocks so that a lot of the many slight differences in their sizes can be accommodated.    

The concept is simple, but slightly unorthodox. If we shape slight angles on the faces of the blocks we can seemingly 'stretch' the height or width of the stones so as to make up for minor variances of the tons of random sized leftover granite blocks we have decided to try to use up. many of the blocks with angled faces touch on face edges only but are pinned to not slip (or tilt) backwards or sideways. 

For example, shown here, a 5 by 3 inch block face can be shaped to have an angle that, after it is tapered length-ways too, can fit into a slightly larger 5 1/8 by 3 1/8 face opening.

(Btw, odd-sized openings like these often occur as we are building.  They are caused by adjacent blocks being slightly different sizes) 

This only works of course because the wall is concave along both its length and height. It gives us our wiggle room. We've started the vertical concaveness by laying the ground row of diagonally positioned blocks so that they lean back nearly 30 degrees. 

(The wall is 28 inches thick and the back of the wall is built up as we go to give it the proper thickness and mass. We eliminate any slippage too as we integrate our blocks into the middle of the wall we've been backing up.)

As you can imagine building a wall this way is a bit confounding. None of the faces of the stones in the wall are on the same plane.