As in all underground mines, there was a need for long utility holes at LKAB Malmberget. The Wassara water powered DTH drilling system is the preferred method when connecting different sub-levels with electrical service, communication, water drainage etc.
Accuracy and performance
Utility holes are usually much longer than the blast holes in a mine. Using conventional blast hole drilling systems, such as top-hammers and air DTH, can be challenging due to the length of the holes and required accuracy. More common is to use a rotary, non-percussive drill rig. But this rig is supposed to drill core samples which is a high prioritized application in many mines. Drilling utility holes with a rotary, non-percussive drill will also be very time-consuming and cost full.
The Wassara solution
With a Wassara drilling system, it is possible to drill straight holes without sacrificing performance and also gaining a better working environment as a bonus.
Wassara’s DTH hammer is powered by high pressure water at up to 180 bar (2 600 psi), resulting in unrivalled performance. When the water leaves the hammer, the pressure is reduced to atmospheric level as it is an open system. This ensures a low up-hole velocity, still powerful enough to bring any cuttings to the surface and to clean the borehole.
Drilling utility holes at the Malmberget mine
The mission was to drill downwards from the main decline in the mine at level 1 100 m (3 600 ft) for an electric installation at sub-level 1 250 m (4 100 ft).
Superior hole accuracy
Key benefits using water, a non-compressible medium to power a DTH hammer;
- Low flow, meaning less annulus space is needed to evacuate the cuttings.
- Low up-hole velocity, meaning minimum wear on drill string when flushing cuttings to surface.
The Wassara hammer casing can therefore be guided / stabilized, enabling a tight tolerance between the bit and hammer. The result is superior hole accuracy. Additional guided drill rod(s) can also be added to further improve the accuracy.
Besides powering the hammer and flushing the cuttings to surface, using water as propellant brings other advantages. The water binds dust and also lubricates the hammer, eliminating any need for oil. Meaning:
- No oil mist in the air!
- No dust, no silicosis!
This is particularly important for underground work where ventilation is limited.
If a large diameter utility hole is needed but the mine layout or infrastructure only allows a small drill rig, not capable of running the optimal sized Wassara hammer. An alternative solution is to first pilot a smaller hole, then open up to the desired hole size, using an special hole opener bit.
But best performance and most cost effective solution is when configuring the Wassara drilling system according to the Product Selection Guide.
Compact drill rig (AC Simba 262)
High pressure water pump, WASP100E