Let's install our keystone bags. Hold off on laying the next row of barbed wire. While still on the ground, prepare three keystone bags;add two cans of dirt to each bag, diddle the corners, and tamp them on the inside with a quarter pounder. Cradle each one in chicken wire.
Neatly place all three bags side-by-side into the open wedge above the arch form (Fig. 6.61). After arranging the bags as symmetrically as possible, use a blunt stick or the handle of the quarter pounder to tamp the inside of each keystone bag.
Add two more cans of dirt and tamp the full interior width of each bag. Use firm, consistent pressure in all three bags. Treat them as one single unit. It helps to have two people tamping while a third provides the fill and quality control on how the bags are shaping from the best vantage point (Fig. 6.62).
Continue the process of tamping and filling, always adding the same amount of dirt to each bag. The bags will widen and widen until the open wedge space disappears (Fig. 6.63).
The keystone bags usually top off at the same 12-inch (30 cm) height as the other fan bags. That's it! Fold the tops of the bags over, cutting off any excess material and pin them closed tight with nails (Fig. 6.64).
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