The Double Helix structure (DNA molecule!) is built
from two square columns that rotate as they rise to a height of 12 feet,
their 9 tons of stone supported only by the
tie-slabs spaced evenly between the columns.
This was a bold attempt at building the world's first permanent
double helix dry stone structure, based on a (first ever) temporary
structure constructed last winter at an advanced DSWAC dry stone
workshop, held indoors at Ground Covers Unlimited in Bethany
Ontario.
The vertical walls of this helix twist around each other, held
together only by large stone rungs placed every 16 inches up the
structure. This Rubble Helix rotated to over 140 degrees.
The demands on the wallers were extensive. Each stone is
actually a corner stone and each layer "corbels" out from the
previous layer. Each layer must be perfectly level and each column
sized accurately to balance with its mate. As the structure rose,
scaffolding was required to reach the top, and a chain hoist was needed
to raise the rung slabs into position.
Although
it looks quite precarious, Bob Moss, a well known engineer who lives in
Port Hope, Ontario assures us that it is quite structurally sound.
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