Civil Engineering Reference
In-Depth Information
Pulley
Safety cage
High power motor unit
Drill rod
Fig. 6.5
Rotary drilling rig.
Sonic drilling
A recent development in drilling technology is sonic drilling. This process involves the use of a sonic drill
head at the ground surface that is vibrated at various high frequencies controlled by the operator, depend-
ing on the particular ground conditions being encountered. The equipment is the same as used for rotary
drilling except for the sonic drill head addition.
The head contains the conventional rotary drilling/coring mechanism and is fitted with an oscillator. The
oscillator sends high frequency vibrations, generally between 50-150 Hz, down the drill rods and sampler
barrel. This means that during operation the drill bit is rotated, advanced and now also vibrated into the
ground. These three components of the drilling energy allow the drill to proceed rapidly through the
ground including drilling through boulders and most types of rock. In physical terms, the resonance of
the vibrations increases the amplitude of the drill bit that enables rapid advancement of the borehole
to be made. Indeed sonic drilling can advance a borehole up to 5 times faster than conventional rotary
drilling. Sonic drilling is also useful for retrieving continuous, relatively undisturbed, soil samples and
rock cores.
