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The water-powered drilling doesn't erode the borehole (left) 1. With Wassara 2. With air-powered DTH

Water-powered drilling gives straight boreholes

As the lower wear on the equipment enables water-powered equipment to use ribs, it gives the possibility to use as little as 1-2 mm clearing between the hammer and the borehole wall. And with the narrower clearance comes the straighter borehole. Several tests indicate a borehole deviation of 1-2% of a 200 meter borehole, to be compared to 15-20% with comparable drilling technologies

Low up-hole water velocity is preferable for high borehole quality

Preferred up-hole velocity of the water is ½-2 meters per second, enough to carry drill cuttings and debris to the surface without eroding the borehole. When drilling with air-powered equipment, the expanding air gets a velocity of 40-80 meters per second.


The formula for calculating kinetic energy is
In this example, we use one grain of drill cutting that weighs 1 energy unit.

With water-powered drilling, we use the water velocity of 1 m/s and will get E=(1x12 )/2= 0.5
With air-powered drilling, we use the air velocity of 50 m/s and will get E=(1x502 )/2=125


Drilling with air-powered technology gives each drill cutting 2500 times higher energy than water-powered drilling gives at the velocities mentioned in the example. The difference gets even larger if the air velocity is increased.

The air sweeps away the drill cuttings, but it also brings along problems like sand blasting the equipment and eroding the borehole. It also gives a dust situation at the surface.


Low up-hole water velocity is preferable for high borehole quality

When drilling with water-powered equipment, there is no risk of eroding the borehole or expanding any cavities. And as the drill cuttings are flushed away, they will not be pressed into the surface of the borehole. This gives a borehole that is optimal for a following grouting process.