A drilling rig, in construction and quarrying, is a self-propelled machine that drills holes into rock or soil from the surface. The holes may be filled with explosives to break rock in a quarry or road cut, fitted with steel anchors to hold back a slope, used as boreholes for geothermal heat pumps and water, or sampled to investigate the ground before a project starts. This entry covers surface drill rigs of these kinds. Underground drilling jumbos and foundation piling rigs have their own entries.
Surface drill rigs range from small crawler machines that can be carried into a basement to large blast hole rigs weighing many tens of tonnes. What they share is a feed, or mast, that guides the drill string, a drilling unit that turns and in many cases hammers the drill bit, and a system to flush the cuttings out of the hole.
Brief History of Drilling Rigs
For most of history, holes for blasting were drilled by hand, with a steel bar struck by hammers. Steam and then compressed air rock drills appeared in the nineteenth century, largely driven by tunnelling and mining, and pneumatic drills mounted on simple wagons became the standard surface tool in the first half of the twentieth century.
Crawler-mounted pneumatic rigs, supplied with air from a separate compressor, spread from the middle of the century. Hydraulic rock drills were introduced in the 1970s and offered higher penetration rates, lower noise and better energy efficiency, and self-contained hydraulic rigs with an onboard compressor for flushing followed. Down-the-hole hammers, where the hammer travels down the hole behind the bit, developed alongside top hammer drilling for larger and deeper holes. Since the 2000s, rigs have gained enclosed cabs with dust control, rod handling systems, GNSS navigation, drill plan software and, on some models, automated drilling.
How a Drilling Rig Works
- Carrier. Most rigs use a crawler undercarriage with oscillating track frames so they can climb benches and uneven ground. Some are mounted on trucks or on excavators.
- Boom and feed. A boom positions the feed, a long beam that guides the drill string and carries the drilling unit up and down. The feed can be tilted for angled holes.
- Drilling unit. A top hammer rock drill hits and rotates the rods from above. In down-the-hole (DTH) drilling, a rotation head turns the pipes and a pneumatic hammer at the bottom strikes the bit. In rotary drilling, the bit cuts or crushes the rock with rotation and high pull-down force alone.
- Flushing. Compressed air, water or drilling fluid clears the cuttings from the hole and cools the bit.
- Rod handling. A carousel or rod changer adds and removes rods as the hole gets deeper.
- Dust collection. A dust collector or water mist system captures the fine cuttings at the collar of the hole.
Types of Drilling Rigs
Top Hammer Rigs
Top hammer rigs are the most common machines in quarries, road cuts and construction blasting. They are fast in hard rock for holes of roughly 30 to 130 mm, but efficiency drops in deep holes because energy is lost along the rod string.
Down-the-Hole Rigs
DTH rigs drill larger and straighter holes, typically from about 90 mm upwards, and keep their penetration rate in deeper holes. They are used for larger blast holes, water wells, anchors and geothermal boreholes.
Rotary Blast Hole Rigs
Large rotary rigs are mainly found in open pit mines. They drill very large holes in softer rock using tricone bits and high pull-down force, and are beyond the scale of most construction work.
Anchor and Micropile Rigs
Compact, versatile rigs used by geotechnical contractors to install rock and soil anchors, soil nails, micropiles and drainage holes. They often work with duplex or overburden drilling systems that case the hole through loose ground.
Geothermal and Water Well Rigs
Truck or crawler rigs designed to drill boreholes of 100 m or more for ground source heat pumps and water supply, often with DTH hammers, mud pumps and pipe handling cranes.
Site Investigation Rigs
Smaller rigs that recover soil and rock samples, perform penetration tests and install monitoring wells. Methods include rotary coring, sonic drilling, cable percussion and direct push.
Size Classes
| Class | Typical operating weight | Typical hole diameter | Typical use |
|---|---|---|---|
| Compact | under about 10 t | up to about 115 mm | Anchors, trenches, urban and restricted sites |
| Medium | about 10 to 20 t | about 64 to 127 mm | Quarries, road cuts, construction blasting |
| Large | about 20 to 40 t | about 90 to 200 mm | Large quarries, deep holes, DTH drilling |
| Mining rotary | over about 40 t | about 150 mm and more | Open pit mines |
Figures are indicative.
Main Manufacturers
- Epiroc, formed from the mining and infrastructure businesses of Atlas Copco.
- Sandvik, which includes the former Tamrock business.
- Furukawa Rock Drill, a Japanese specialist in hydraulic drill rigs and breakers.
- Comacchio, Casagrande, Soilmec and Klemm for anchor, micropile and geotechnical rigs.
- Geoprobe Systems for direct push and site investigation rigs.
Main Uses of Drilling Rigs
- Blast hole drilling in quarries, road and rail cuts and construction excavations.
- Rock and soil anchors, soil nails and rock bolts for slope stabilisation.
- Micropiles and foundation reinforcement.
- Geothermal boreholes and water wells.
- Geotechnical and environmental site investigation.
- Drainage and grouting holes for dams and embankments.
Planning Drilling Work
- Match the method to the hole. Top hammer drilling is usually the most productive for small holes in hard rock. DTH gives straighter, deeper holes. Loose overburden may require cased drilling systems.
- Drill to a plan. Accurate hole position, angle and depth are essential for good blasting results, fewer oversize rocks and safer faces.
- Consider access. Steep benches, narrow ledges and urban plots may favour compact or remote-controlled rigs.
- Plan air and fuel. Flushing air is a large share of energy use, so compressor size and settings affect fuel consumption.
- Budget for consumables. Bits, rods, shanks and hammers wear quickly in abrasive rock and are a major operating cost.
Safety
Drilling rigs work close to bench edges, on slopes and around explosives, so stability and edge protection are basic concerns. Rigs should be positioned on stable ground and travel with the feed lowered. Rock dust containing crystalline silica is a serious health hazard, which is why enclosed pressurised cabs, dust collectors and water flushing are important. Other hazards include rotating rods, rod handling, high-pressure air and hydraulic hoses, noise and contact with buried services or overhead lines. Drillers must also take care around holes that have already been charged with explosives and follow the blast plan.
Trends and Technology
Modern surface rigs use GNSS navigation and drill plan software to position each hole without marking it on the ground, and record the data for the blasting engineer. Measure-while-drilling systems log penetration rate and other parameters, which gives information on rock quality. Automated functions such as auto-rod handling, auto-collaring and complete hole automation reduce operator workload, and some rigs can be operated remotely from a control room. Battery electric and cable electric versions are appearing, and diesel rigs are becoming more efficient through variable-speed compressors and engine management.
Dust and noise are also receiving more attention. Better cab filtration, water mist systems and noise-reducing feed covers help rigs work closer to homes and in urban excavations, where planning conditions often limit working hours and emissions.
Key Terms
- Top hammer: drilling with the percussive rock drill at the top of the rod string.
- DTH hammer: a percussive hammer that works at the bottom of the hole, directly behind the bit.
- Feed: the beam that guides the drill string and carries the drilling unit.
- Flushing: removal of cuttings from the hole with air, water or fluid.
- Overburden drilling: cased drilling through loose soil above rock.
- Burden and spacing: distances between rows and holes in a blast pattern.
Frequently Asked Questions
What is the difference between top hammer and DTH drilling? A top hammer rig strikes the rods from above, which is fast in small holes. A DTH rig places the hammer at the bottom of the hole, which suits larger and deeper holes and keeps them straighter.
Do drilling rigs need a separate compressor? Most modern hydraulic surface rigs have an onboard compressor for flushing. Older pneumatic rigs and some DTH work use separate portable compressors.
How deep can a surface drill rig drill? Quarry blast holes are often 10 to 30 m deep. Geothermal and water well rigs can reach 100 to 300 m or more, depending on the machine and ground.
Are piling rigs and drilling rigs the same? They share some principles, but piling rigs build foundation piles of large diameter, while surface drill rigs make smaller holes for blasting, anchors, wells and investigation.
Can a drill rig be operated remotely? Many modern rigs can be operated by radio remote control from a short distance, and some large rigs can be supervised from a remote control room, with the operator monitoring several machines at once.
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