Quarry & Open Pit Drilling: These can be categorised as Air or Hydraulically operated. The operator stands by the front of the rig to operate the controls and change extension pipes. The Airdrill is wholly propelled by air supplied from separate compressor. The Airdrills are normally mounted on crawler tracks supporting a boom & vertical chain feed (a.k.a. the mast) upon the mast is attached a drilling head of which there are two types.
Drifter Drill: Very similar to jack hammer used to break up pavement but has an additional rotational feature. Usually used in shallow small diameter holes. Penetration (the drill rate) is fast at the beginning, but speed decreases with each additional steel added. The Rig has to withstand much of the drilling impact and vibration. This type of drill is usually used on small or irregular benches.
Top Head Rotation: This is Air or Hydraulically driven & can drive a Rotary Bit or "Down the Hole Hammer" (DTH). Penetration is a constant speed to all depths. The air which drives the Hammer also cleans the hole. All the energy goes into the rock and not the Rig.
Benefits of either:
A rotational head (DTH) uses drilling pipes which are larger in diameter and lead to straighter hole with very little deviation. The actual hole size is usually a minimum of 4" in diameter. The consumption of air is normally the same, but a minimum of 12 bar (170psi) up to 24bar (350psi) pressure is required. The capability of the machine has to be matched to the type of the rock to be drilled. Usually harder formations need higher air pressure. The DTH drill requires a more expensive compressor to operate it at a higher pressure together with the increased running costs. These drills are usually used in quarries with deeper and wider benches. As the larger diameter hole accommodates a larger charge of explosives, the results are usually a more uniform size of aggregate and speeds up handling and the subsequent crushing phase.
A drifter Rig operates a drill steel which is usually 38mm in diameter and flushes the drilled debris from the hole by way of a small diameter vent through the drill steel which has a tungsten carbide drill bit attached to the end. The bit can be as small as 2" & up to 3.5" in diameter. The drifter operates both rotation and hammer actions from the mast (above ground) transmitting shock waves down the drill steel to produce a rotating & percussive effect on the bit. A consideration must be the excessive wear on the couplings and drill steel threads from the constant impact and vibration.
Drifters consume less air for smaller diameter holes. This requires a lower pressure compressor which in turn consumes less fuel & reduces subsequent running costs. Drifters cannot use high pressure air, as this causes "bit bounce" and frequently breaks the tips from the bit or fractures the couplings.
Hole deviation can be a problem with this type of drilling, as the smaller diameter drill steel bends under pressure or can be deflected in broken or fractured strata. The consistency of the rock size produced can then be a problem.
Fully Hydraulic Drills: Same basic design as an Airdrill, can either be equipped with "down the hole" (DTH) or Drifter type drilling heads. All functions are driven by an onboard diesel engine mated to high pressure hydraulic pumps at one end and a small air compressor (for hole flushing) at the other. These can weigh from 8 tons for 2.5" (63mm) dia. holes up to 25 tons for maximum hole size of 6" (150mm) diameter. Larger holes = larger drills 8"-10" (200-250mm) could be up to 75tons. The advantages of straight holes by the "down the hole" method is not so pronounced here - as the extra power of the hydraulic rig means the drifter can handle a larger diameter "starter" rod helping to minimise deviation.
Production from hydraulic rigs is much higher than an Airdrill, but they carry a higher initial capital cost and require skilled engineers to maintain and repair them. The smaller hydraulic drill is usually operated by an attendant standing alongside, similar to an Airdrill. The larger rigs generally have fully enclosed cabins, the exposed attendant is now discouraged on Insurance and Health & Safety grounds by most larger European Quarry Operators. Small & developing projects still use the standby attendant with either the air or hydraulic rigs.
Water Well Drilling Rigs:
Mobile Water Well Drilling rigs: Most Water Well Rigs are mounted on road going trucks to speed mobility on and between sites. Some smaller Rigs are now mounted on rubber tracked caterpillar type undercarriages, these have to be loaded on truck or trailer to transport.
They range in size from 5-10 tons for smaller diameter wells (4-6") at shallow depths (100 metres approx.) up to 25-35 tons for 6-8" holes drilling down to 300 metres.
Drilling Methods: "Down the Hole" is usually preceded by the overburden being drilled by Rotary Drill Bit and the hole stabilised with steel casings driven down and "toed" into the hard rock. This is the most common method. Ongoing bailing or cleaning the hole can be effected by either air or mud sometimes a combination of both depending on the type of overburden & rock formation. The smaller drills can be mounted on rubber tracks for increased manoeuvrability.
Rigs come equipped with their own prime mover to power the hydraulic pumps. Additional equipment is often fitted by the manufacturer, i.e. mud pump, air compressor, water pump or electric welder (to weld steel casing) Apart from the Rigs horsepower (75hp for a small unit to 450hp for a 25 ton truck mounted unit), Pulldown & Pullback are a Rigs important specification. Pulldown equates to the downward pressure mounted on the drill string. Most importantly Pullback is the term used to describe the units total power, that it is able to apply when recovering the drill string from the hole. Extra power over and above normal requirements is often called for, when trying to recover jammed drill strings in broken rock or a backfilled drill head, due to the hole collapsing and or poor hole bailing capacity.
Some inexperienced owner/operators believe that hole diameter and depth is the most important parameters and subsequently drill to depths far in excess of the Rig ability to Pullback the drill string, often with expensive consequences.
Ground Engineering Drills:
Engineering Drills are used for soil investigation, ground anchoring, stabilisation, grouting, core drilling, mini piling and auguring to name but a few!
These rigs are very powerful & versatile sometimes rotating 360 degrees, similar to an excavator. The boom and mast have to be manipulated at tight acute angles to engage in anchoring & underpinning. All these rigs are mounted on heavy caterpillar tracks and have a powerful diesel engine driving a combination of hydraulic pumps to power multiple tasks simultaneously.
