| Loosening by ripping
As with the
cutting procedure, ripping hard soils or rock is accomplished by an inclined
tooth which cuts a small groove into the soil during rotation of the boring
tool. The remaining soil or rock is easily removed by the flat scraper
teeth. Since the teeth have the tendency to rise upwards, drilling tools
have to be pushed downwards during rotation. With the use of drilling
rigs equipped with torque rotary drives and push down facilities for drilling
tools, and as a result of the development of extremely strong ripping
teeth, it is now possible to drill into rock with a strength of up to
100 kN/mm2.
Such tearing
teeth, also called round shank chisels, can be mounted on augers and drilling
buckets in combination with flat scraper teeth.
When drilling
into very hard soils, it is more efficient to first cut an outer annulus.
Stress release can then occur in the remaining core, enabling it to be
easily broken up and removed.
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