Raise Boring Machines

A raise boring machine, or raise borer, is a drilling rig used to excavate vertical or steeply inclined shafts between two levels of a mine or tunnel system. In the classic method the machine sits on the upper level, drills a small pilot hole down to the lower level, then a large reaming head is attached to the drill string at the bottom and pulled back up, cutting the full shaft diameter as it rises. The cuttings fall down the shaft by gravity and are removed from the lower level with loaders.

Raise boring produces smooth, round shafts with little damage to the surrounding rock, and it keeps workers out of the shaft during excavation. The shafts, known as raises, are used for ventilation, ore and waste passes, service and escape ways, and in civil engineering for penstocks, pressure shafts and ventilation shafts in road and rail tunnels. The method replaced much of the hand-mining of raises, which was slow and among the most dangerous jobs underground.

Brief History of Raise Boring Machines

Before raise boring, raises were usually driven upwards by miners working on timber platforms, drilling and blasting over their heads, or later using mechanised climbing platforms. These methods exposed workers to falling rock, blast fumes and difficult access.

The first successful raise boring machine was developed by the Robbins Company in the United States in 1962, building on its experience with tunnel boring machines. The idea of drilling a pilot hole from above and reaming upwards made use of rotary drilling technology from the oil and mining industries combined with rock cutters developed for TBMs. The method spread rapidly through hard rock mining in the following decades. Machines became more powerful, allowing larger diameters and longer holes, and down-reaming, blind boring and box hole methods were developed for situations where access to one level is not available. The Robbins raise boring business later became part of Atlas Copco, and today it is part of Epiroc.

How a Raise Boring Machine Works

Set-up. The machine is anchored to a concrete pad on the upper level. The derrick, which carries the drive head, is set to the required angle, from vertical to steeply inclined.
Pilot hole. A pilot bit drills down through the rock, using drill rods added one by one. Cuttings are flushed up the hole by water or air. Directional drilling systems can be used to keep the pilot hole straight on long holes.
Breakthrough. When the pilot bit reaches the lower level, it is removed and a reaming head is fitted to the drill string.
Reaming. The machine rotates and pulls the reamer upwards. Disc cutters on the reamer crush the rock, which falls to the lower level. Rods are removed one by one as the reamer rises.
Drive system. Electric or hydraulic motors provide rotation through a gearbox, and hydraulic cylinders provide the thrust for pilot drilling and the pull for reaming.
Control. The operator controls the machine from a nearby console or cabin, monitoring torque, thrust, speed and penetration.
Muck removal. Loaders remove the broken rock from the bottom of the raise as the reaming progresses.

Types of Raise Boring Methods

Conventional Raise Boring

The standard method, with the machine on the upper level drilling a pilot hole down and reaming up. It requires access to both levels.

Down-Reaming

A pilot hole is drilled and then enlarged downwards, often after a smaller raise has been reamed up to give a path for cuttings. It is used for very large shafts.

Blind Boring

The machine drills the full shaft from above without access to the bottom. Cuttings must be lifted back up the hole, usually by reverse circulation. It is used where the lower level does not yet exist.

Box Hole Boring

The machine sits on the lower level and drills upwards, pushing the reamer up without a pilot hole reaching another level. It is used for short raises where the upper level is not accessible.

Mobile and Compact Raise Borers

Smaller self-propelled rigs for short raises, slot raises and service holes, designed to be moved quickly between locations in a mine.

Size Classes

Class	Typical raise diameter	Typical use
Small	about 0.6 to 1.5 m	Slot raises, service holes, drainage holes
Medium	about 1.5 to 3.5 m	Ventilation raises, ore passes, escape ways
Large	about 3.5 to 6 m and more	Main ventilation shafts, penstocks, large ore passes

Figures are indicative. Achievable diameter and length depend on the machine, the rock and the method, and hole lengths range from tens of metres to well over 1,000 metres on the largest machines.

Tools and Accessories

A raise boring job relies on a set of tools that are chosen for the rock and the size of the raise. Pilot bits, usually tricone roller bits, drill the pilot hole. The drill string is made of heavy threaded rods, often with stabilisers that help keep the pilot hole straight. Reaming heads are fitted with disc cutters and come in fixed sizes or in modular designs that can be expanded to different diameters. Other equipment includes rod handling units, hydraulic power packs, electrical switchgear, flushing pumps and, for long holes, directional drilling tools and survey instruments to check the position of the pilot hole.

Main Manufacturers

Epiroc, which continues the Robbins raise boring line that passed to Atlas Copco.
Sandvik, with its Rhino raise boring rigs for mining.
Terratec, a manufacturer of raise boring machines and other tunnelling equipment.

Specialist contractors, such as the South African company Master Drilling, operate large fleets of raise borers around the world.

Main Uses of Raise Boring Machines

Ventilation raises and shafts in underground mines.
Ore and waste passes between mining levels.
Slot raises to start stopes in sublevel and longhole mining.
Escape and service ways, including cable and pipe shafts.
Penstocks and pressure shafts for hydropower schemes.
Ventilation and access shafts for road and rail tunnels.

Planning a Raise Boring Job

Check the rock. Rock strength, abrasiveness and fractures affect cutter wear and the stability of the finished raise. Weak zones may need support or grouting.
Keep the pilot hole straight. Deviation increases with depth. Directional drilling or a larger pilot bit may be needed on long holes.
Size the machine for torque and pull. Larger diameters and longer holes need much more torque and pull capacity.
Prepare the site. The upper level needs space for the machine, rod handling, a concrete pad, water and power supply, and good access for transport.
Organise muck handling. The lower level must be ready to handle cuttings as they fall, and the area must be closed to people during reaming.

Safety

Raise boring removes workers from the shaft itself, which is its main safety advantage. The hazards shift to the drill site and the lower level. At the machine, risks include rod handling, rotating parts, high-pressure hydraulics and heavy lifting of reamers. At the bottom of the raise, rock falls continuously during reaming, so the area must be barricaded and no one should enter it while reaming is under way. Rod handling systems, remote monitoring and interlocked barriers reduce exposure. A completed raise in poor ground may need inspection and support before it can be used.

Trends and Technology

Raise boring machines are gaining more automation, including automatic rod handling and drilling control that adjusts thrust and rotation to the rock. Remote monitoring allows specialists to follow drilling from the surface. Larger machines can bore longer and wider raises, while compact rigs make the method practical for shorter raises. Directional drilling systems help to keep long pilot holes on target. Electric drives, already standard on most machines, fit well with the move towards low emission mines.

Key Terms

Raise: a vertical or inclined opening connecting two underground levels.
Pilot hole: the small diameter hole drilled first to guide the reaming.
Reamer: the large cutting head that enlarges the pilot hole to the final diameter.
Derrick: the frame that carries the drive head and sets the drilling angle.
Box hole: a raise bored upwards from below with no access at the top.
Blind boring: full-diameter boring from above without access at the bottom.

Frequently Asked Questions

What is the difference between raise boring and shaft sinking? Shaft sinking excavates a shaft downwards from the surface, usually with drill and blast or shaft boring machines. Raise boring normally needs access to both ends and reams upwards from a lower level.

How long does it take to raise bore a shaft? It depends on the diameter, length and rock. Pilot drilling and reaming can take from days for short raises to several months for long, large shafts.

Why does the reamer cut upwards? Cutting upwards lets the broken rock fall away from the reamer, so the cutters always work on fresh rock and no system is needed to lift cuttings.

Can raise borers drill inclined shafts? Yes. Many machines can drill at angles away from vertical, although steep angles are preferred so that cuttings fall freely.