With roots tracing back to the first half of the 20th century, roadheaders have a long history in the underground construction industry on a wealth of applications including tunnels, mines and other underground structures. Their small footprint, maneuverability and adaptability make them the right choice on a number of jobs.
So what type of jobs are ideally suited to the use of a roadheader? How have they evolved to meet the needs of an underground contractor? To find out, TBM: Tunnel Business Magazine contacted Karl Mitterndorfer, president and CEO of Antraquip Corp., based in Hagerstown, Maryland. Founded in 1985, Antraquip has become a worldwide manufacturing leader of reliable roadheaders, innovative rock and concrete rotary drum cutting attachments, tunnel support systems and supplier of other specialized machinery for the construction, mining and the tunnel industries.
Mitterndorfer shared his views on the status of roadheaders in today’s underground construction industry, the latest developments in roadheader technology, and tips for getting the most out of your machine.
Describe the use of roadheaders in the tunnel market today? Is it increasing? Decreasing? Why?
Roadheaders are the preferred way of excavating tunnels in soft to medium hard ground, mainly for tunnels that are up to 1 ½ miles long provided that the hardness (unconfined compressive strength) of the material to be excavated is not in excess of 20,000 psi UC for smaller machines and 30,000 psi for the largest machines.
The market for roadheaders naturally depends on the political situations, the availability of financing, and naturally on the tunnel designers, who frequently will determine in their plans either to use a roadheader or another means of excavating.
Over the last several years, the market for roadheaders in North America was relatively quiet. Looking forward, there are numerous tunnels in the design phase that will be excavated with roadheaders.
What are the advantages of roadheaders in tunneling applications? What are the limitations?
The limitations for roadheaders is the hardness (UCS) of the material to be excavated. At times, the combination of hardness of the material and the size limit for the roadheader limits the operation of a roadheader. Meaning, sometimes you would need a larger machine for the specific rock excavation, but you do not have enough space to do that.
Normally, the heavier the machine, the higher the production and the higher the ability to cut harder rock. Today, roadheaders are manufactured with a cutter motor power up to 400kW, an operating weight up to 150 tons and the ability to cut material with a UCS of up to 30,000 psi.
The advantages of roadheaders are:
A) COMPARED TO DRILL AND BLAST:
- No over cut
- Higher production in most cases, depending on material
- Less vibration
- Less noise
- Less fracture of nearby rock, construction etc.
B) COMPARED TO TBM:
- higher versatility
- less capital investment
- ability to cut different tunnel shapes and tunnel profiles
What Types of Projects Lend Themselves to Roadheaders vs. Other Methologies?
Most uses of roadheaders are:
- In large short sections, like stations on new subway lines, in soft to medium hard ground
- For excavation of starter tunnels and tail tunnels for TBM projects
- For smaller utility tunnels due to size limitations
- For special complex geological projects, even if the tunnel is longer, but the use of a TBM is not acceptable due to high risk of the TBM getting stuck
- For excavation of stations in harder material, if drill and blast is either forbidden or complicated.
How has roadheaders technology evolved? What are the latest advancements?
The challenge to be able to cut harder and harder rock keeps going on and on. And still the limit is the usage of cutting tools (cutter picks) to make it efficient and economical. Currently, the largest roadheaders with up to 400 kW cutting power can cut material up to 30,000 psi. Is it efficient and economical to cut material that hard? Depends on the circumstances, like abrasivity of the material to be cut, other possible ways of excavation, etc.
More and more additional tools can be installed on the roadheader, sometime even on the same machine. For example, the same roadheader can be equipped with a drill for forepoling and a drill for roof-bolting.
Increased Safety Standards
Additional substantial improvements have been made on safety.
- Installation of proximity systems, which will shut down the machine if an unauthorized person is getting to close to the operating machine. This also will help avoiding run-ins between the roadheader and the loader or scoop tram to remove the material.
- Dust control is very critical. Consequently, all larger roadheaders can be equipped with air conditioned closed cabins to protect the operator from breathing dust particles etc.
- Remote capabilities have been improved. Roadheaders can be operated remotely on distances of several hundred feet.
- Automatic guidance systems can be installed.
What should a contractor look for when purchasing a roadheader?
Every project that considers a roadheader is different. Therefore, when purchasing a roadheader the utmost importance is that the roadheader is able to do what is expected as to production, speed of excavation, etc.
Therefore, only use a reputable supplier with a proper track record. Also make sure you not only ask questions, but also check out the track record.
Secondly, you want to rethink what you plan to do with the roadheader after the project is finished. Do you want to keep it in your fleet or do you want to resell it or sell it back to roadheader manufacturer? If you want to add it to your fleet, you should consider a machine that can be used in numerous set ups.
Since roadheaders are working and have been working in very difficult projects, the availability of professional support and prompt – overnight – spare part supply is a necessity. It does not help you if parts have to be flown in from overseas, which will – at best – take days before the parts are available at the jobsite.
What advice can you give a contractor to help get the most out of the machinery? (Operating tips, maintenance tips, etc.)
First, pick the right size of roadheader. Unless there are other reasons (like space limitations) try not to run the roadheader in harder material than it was designed for. Also try not to run it at the maximum hardness allowed.
Continued service as per operating instructions is of utmost importance.
Also, follow all other guidance in the operating manuals as closely as possible.
Replace cutter bits when necessary. Follow the instructions in the operating manual.
And, most important, if you feel, hear or see anything not normal, figure out the problem – either by yourself or with help from the manufacturer – and repair the issue immediately. Problems do not disappear by themselves and only get worse over time.
Roadheaders remain an important part of the modern-day tunneling industry. For the right project, there is no better way to excavate the tunnel; however, it must be within the criteria as outlined earlier. In North America, the number of roadheaders operating at any one time depends on many factors, including, but not limited to, the design of the projects by the tunnel design firms.