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Large rocks or boulders that are in the way of the construction, need to be
broken up:

First a hole is drilled into the middle of the bolder.

Next, two
tongue type wedges are placed into the hole with a third tapered wedge
placed in the middle.
The middle wedge is then 'sledge-hammered'
in causing the two outer wedges to be pressed out against the rock.

Within a short period, the rock will split
into several pieces.
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