The concept of small bore rotary rock drilling or slimhole drilling as it’s known in the USA or microdrilling a term which has recently been coined in the UK has been around since the late 1950s. The method requires a powerful self- propelled compact drill rig capable of advancing a small diameter drill string at high speed with reduced quantities of flushing medium.
Because of the drills small size and because it creates less noise, needs less water and generates less drill waste the method offers a cost effective solution to drilling in difficult access sites, sensitive urban locations and in buildings where space is tight. Site disturbance and reinstatement costs are reduced.
Since the introduction of very small geotechnical rigs in the last decade in the UK efforts have been made particularly in the last 5 years to adapt these micro-drilling machines to incorporate fast small bore rotary rock drilling applications including mine working probing, shaft and adit identification, quarry and infilled ground delineation and finding rock head for piling.
Some small rigs even offer inclined or declined drilling, capability making it possible to drill under buildings or obstructions to reach the required target position. The use of water flush or aerated foamed water makes them safer for drilling into mine workings where there may be the risk of combustion or explosion.
Typically these small drill rigs weigh in around 800 kgs to 1.1 tonne. Images of several of the rigs which are currently available to the UK microdrilling market are presented below.
Over the past year Geonvestigate has tested several rigs to evaluate their capability and efficiency with various degrees of success. Of these TecopSa’s T15 is probably the cheapest probably because it is made in Spain !
All are small, look the part and can perform a range of functions from augering to window sampling, rotary open hole drilling, coring and even DTH. But is a jack of all trades master of none?
Geoinvestigate’s recommendation is that if your thinking about investing in microdrilling you need to do your research – weigh rig size against output power, build quality, rotary speed and advance rate to avoid disappointment.