Layout Pt.2 That can't be right.

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A new day, a new week, a new month and having enjoyed a complete rest day yesterday, I shall start digging for the grand sinking of the [concrete] stone circle. All the plans of mice and men.. l hit a series of large rocks from the dry stone wall retaining the original shed foundations. It took two whole hour to remove one large boulder which was buried deep in the original soil. Once free of the soil I used various levers and kept adding split logs beneath it to slowly raise the boulder to the surface so it could finally be rolled away across the surface of the sand. This was the technique I used to clear literally hundreds of boulders to remove a steep bank which rested against our old cottage in Wales.

I also discovered a foolish error in the placing of my first concrete footing. By planting it by measuring from the center of the concrete pier pipe I had ignored rotation of the octagon relative to the nearby shed.

There was an error of 10cm/ 4" in the distance of the second footing from the shed. This caused an onward rotation all the way around the "stone circle." So when I arrived at the footing nearest the shed it was much too close. This was despite my accuracy in placing each new footing relative to the last and relative to the center post. Each new footing measurement merely added the error to the next in series.

 
Rather than draw two overlapping octagonals I have shown the rotational error, by drawing the shed wall in red. The correct geometry shows the shed wall in light brown. With two opposed walls now properly parallel with the [brown] shed wall. The error in distance from the shed is shown in purple [above.]

The second image has been simplified to show the distance error of the nearest posts to the shed. I started digging at post hole No1. Had I started at 5 & 6 I would have spotted the error much earlier.

Fortunately I have not back-filled any of the footing holes. So I shall just have to lift the concrete blocks out again and widen each hole anticlockwise to correct the error of rotation.

I can see why this error happened. I set up all the footings on the surface of the sand and measured it all up. Then each footings had to be moved out of the way so that the excavation could be started on the bare sand and gravel. Once the footing was moved away there was no longer any reference points to go by. I just kept digging until the hole was deep and wide enough and dropped in the concrete anchor casting. And so onto the next.

Click on any image for an enlargement.

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