| Rope grab
Since the
shovels of the grab form a cone when closed, the capacity of the grab
and its corresponding rate of excavation per lift is only about 1/3 of
the pile diameter. In order to compensate for the small volume of excavation,
high-speed winches were developed at an early stage.
The time
required to return the grab into the borehole is also minimized by way
of an ejection device attached to the drilling rig.
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