Roadheaders

A roadheader is a tracked excavating machine with a boom-mounted rotating cutting head, used to excavate tunnels, mine roadways and underground chambers in soft to medium-strength rock. Instead of cutting the whole face at once like a tunnel boring machine, the roadheader moves its cutting head across the face in a pattern, milling the rock away section by section. A gathering system at the front collects the cut material and a conveyor carries it back over the machine to a truck, loader or belt behind.

Roadheaders are sometimes called boom-type tunnelling machines or partial-face machines. Their main advantage is flexibility: the same machine can cut horseshoe, rectangular or circular profiles of different sizes, work in short tunnels where a TBM would never pay back its cost, and excavate niches, cross passages and caverns. Because they cut rather than blast, they cause little vibration and produce an accurate profile with little overbreak, which makes them useful in urban areas and next to existing structures.

Brief History of Roadheaders

Roadheaders were developed for coal mining, where the need to drive long roadways quickly through soft rock encouraged mechanisation. An early patent for a roadheader was filed in Hungary in 1949, and during the following decades machines were developed and built in several mining countries in Europe, including the Soviet Union, the United Kingdom, Germany and Austria.

By the 1970s roadheaders had started to move from mining into civil engineering, being used for metro, railway and sewer tunnels in suitable rock. Over time the machines became heavier and more powerful, which extended their range into harder rock. Improvements in pick design, water spray systems, dust extraction, profile control and remote operation followed. Today roadheaders remain common in coal and mineral mines, in tunnel projects with short drives or complex geometry, and in the enlargement and rehabilitation of existing tunnels.

How a Roadheader Works

Crawler chassis. The machine sits on a pair of crawler tracks that move it forward and backward and help hold it in position against the reaction forces of cutting. Some machines have stabilisers or stingers that brace against the floor and walls.
Cutting boom. A hydraulically controlled boom, mounted on a turntable, moves the cutting head up and down and side to side across the face. Some booms can also telescope forward to cut without moving the tracks.
Cutting head. A rotating drum or cone fitted with tungsten carbide tipped picks. The picks break the rock as the head rotates and is pushed into the face.
Gathering and loading. A loading apron at the front uses gathering arms, spinners or star wheels to collect the broken rock and feed it onto a chain conveyor running through the machine.
Conveyor. The conveyor delivers the material at the rear onto a trailing belt, into a loader or into a truck.
Dust and water control. Water sprays at the picks cool the tools, suppress dust and reduce the risk of sparks igniting gas in coal mines. Dust extraction fans are often used as well.
Control. The operator works from a cab or with a remote control, and many machines have profile control systems that guide the cutting head to the design section.

Types of Roadheaders

Axial (Longitudinal) Cutting Head

The cutting head rotates about the axis of the boom, and the head is moved across the face in a sweeping motion. This design suits softer rock and tends to produce a precise profile. It is also good for cutting in a sump-and-shear pattern in mixed ground.

Transverse Cutting Head

Two cutting drums rotate at right angles to the boom, one on each side. The cutting forces push the machine back towards the face rather than sideways, so this design is generally used in harder or more abrasive rock.

Light, Medium and Heavy Machines

Roadheaders are often grouped by weight and cutting power. Heavier machines are more stable, can apply more force and cut harder rock economically.

Boom Cutters and Excavator-Mounted Units

Excavator-mounted cutting heads, known as transverse or drum cutters, perform some of the same work in small tunnels and trenches, but they are attachments rather than dedicated roadheaders.

Continuous Miners

In coal and soft mineral mining, continuous miners with wide cutting drums fulfil a similar role in room and pillar mining, although their design is different.

Size Classes

Class	Typical operating weight	Typical use
Light	about 25 to 50 t	Mine roadways, small tunnels, soft rock
Medium	about 50 to 80 t	General tunnelling, cross passages, metro stations
Heavy	about 80 to 130 t and more	Large sections, harder rock, caverns

Figures are indicative. Cutting head power ranges from under 100 kW on light machines to several hundred kilowatts on the heaviest.

Main Manufacturers

Sandvik, whose MT range of tunnelling roadheaders descends from the Austrian Voest-Alpine machines.
SANY and XCMG, Chinese manufacturers with ranges for mining and tunnelling.
Mitsui Miike, the Japanese manufacturer of roadheaders for civil tunnels.
Antraquip, known for roadheaders and excavator-mounted cutter heads.
Eickhoff, the German mining machinery company, known for coal mining equipment including roadheaders.

Main Uses of Roadheaders

Driving roadways in coal, potash, salt and other soft rock mines.
Short road, rail and metro tunnels in suitable rock.
Cross passages, adits, shaft bottoms, caverns and station chambers.
Enlargement and rehabilitation of existing tunnels.
Tunnels in urban areas where blasting vibration is not acceptable.
Sequential excavation method (SEM or NATM) tunnels with partial-face headings.

Roadheader or Drill and Blast?

Rock strength. Roadheaders are most economical in soft to medium rock. In very hard or abrasive rock, pick consumption and wear rise sharply and drill and blast is usually cheaper.
Vibration and noise. Cutting avoids blasting vibration, air overpressure and the need to evacuate for each blast, an advantage near buildings and existing tunnels.
Profile accuracy. A roadheader cuts close to the design line, reducing overbreak and the amount of sprayed concrete or lining needed.
Continuity. Cutting and mucking happen at the same time, whereas drill and blast is a cycle of drilling, charging, blasting, ventilating and mucking.
Flexibility. Drill and blast adapts to almost any rock and shape. Roadheaders adapt well to changing shapes but are more sensitive to hard bands in the rock.

Safety

The main hazards around roadheaders are dust, noise, contact with the rotating cutting head and conveyor, and falls of ground at the unsupported face. Water sprays and dust extraction are essential to protect workers from respirable dust and, in rock containing quartz, from crystalline silica. In coal mines, methane monitoring and spark suppression are required. Operators increasingly work from protected positions or with remote controls, which keep them away from the face. Ground support should be installed as close to the face as the method allows, and nobody should enter the area in front of the cutting head while the machine is energised.

Trends and Technology

Roadheaders are becoming more automated, with profile guidance, automatic cutting cycles and remote monitoring now common features. Some machines combine cutting with bolting rigs so that ground support can be installed without moving the roadheader back. Development work continues on cutting harder rock, including machines using disc or undercutting technology rather than conventional picks. Electric drives are standard on most roadheaders, which fits the wider move away from diesel underground.

Key Terms

Pick: a carbide-tipped cutting tool mounted on the cutting head.
Axial head: a cutting head rotating in line with the boom.
Transverse head: twin cutting drums rotating across the boom.
Gathering arms: rotating arms on the apron that collect the cut rock.
Overbreak: rock removed beyond the design profile.
UCS: uniaxial compressive strength, the rock strength measure used to judge cuttability.

Frequently Asked Questions

How hard a rock can a roadheader cut? It depends on the machine weight, power and the abrasiveness of the rock. Heavy machines can cut moderately strong rock, but in very hard or abrasive rock the cost of picks and wear usually makes other methods more economical.

Is a roadheader the same as a TBM? No. A TBM excavates the whole face at once with a full-face cutterhead and is designed for one diameter. A roadheader cuts part of the face at a time and can form different shapes and sizes.

Why are roadheaders used in cities? They excavate without blasting, which means less vibration and noise and no need to clear the area for each blast.

What does a roadheader do with the cut rock? It gathers the rock at the front and carries it on an internal conveyor to the back of the machine, where it is loaded into trucks or onto a conveyor.

What wears out on a roadheader? The picks wear fastest and are replaced regularly, often every shift in abrasive rock. Pick boxes, cutting head bodies, gathering arms and conveyor chains also wear and need regular inspection.

Can a roadheader work in coal mines with gas? Yes, machines for coal mining are built to explosion protection standards, with flameproof electrical equipment, methane monitoring and water sprays to reduce the risk of ignition at the picks.