This review gives information about roof support, rockbolting, and shotcrete. Several links, publications, suppliers, and consultants are listed. Links to roof bolting software and online courses are given, as well as case histories and articles specific to shotcreting.
Failure to support the roof of a mine is the greatest cause of accidents in mining. Many a good miner says you can hear the rock talk and so you know to stay away. Colourful, but not sufficient today as the basis for good mining practice. So here is a brief guide to the many resources available free on the web.
Browsing through the many definitions in the InfoMine dictionary under "roof"
is a primer on the topic of mine roofs and their support. I invite you to do so.
In the InfoMine Links database are over thirty links to sites that contain information about mine roof support. The only one you really need is the NIOSH site
. It contains a wide array of information and publications on the topic and is a must if this topic is of interest to you. The rest simply fill in the few voids of the NIOSH site, or worse replicate its information.
Here are ways to improve productivity in underground coal mines. The suggestions are well documented in a seminal paper Roof bolting and mining: are your cycles in tune?
by E.B. Kroeger and M. McGolden published in the January 2007 issue of Mining Engineering
, although you need to be a member to access the paper. You can access for nothing this paper by the same authors on pretty much the same topic: Increasing underground coal mine productivity through a training program.
The paper reports on work funded by the Illinois Clean Coal Institute
. Their conclusion is that there are many variables that have an affect on the productivity from an underground room-and-pillar coal mine.
One of the goals of this paper was to illustrate the need for mines to model their production systems, including their roof bolting cycles, an determine if further improvements can be made. Another goal was to help mining operations quantify the benefits of specific changes so they can make more informed decisions and focus their attention on the most critical issues. These critical issues can then be incorporated into a miner-productivity-training program to increase the productivity from the mine. The work by the authors, their colleagues, and the related sponsor goes some way to achieving the goal of safer, more cost-effective mining, and it is unfortunate that the tools needed to advance are not more freely available
Here is a paper from their site that is related to the paper by Kroeger and McGolden and well worth reading: Development and Demonstration of alternative room-and-pillar mining geometry in Illinois by Chugh et al. Another related paper is Best practices and bolting machine innovations for roof screening by Robertson et al.
Rockbolts and Cables
Rockbolts and cables have been used in supporting the underground excavations for decades and are still the most reliable means of support. Continuous developments can be seen in the area of improved design life, reduced cost, higher loading capacity and in the simplicity of installation. I have listed here the different type of rockbolts and cables currently used in the mines, on which hundreds of articles can be found on the Internet and in InfoMine's database
- Mechanically anchored rockbolts
- Resin anchored rockbolts
- Grouted dowels
- Friction dowels or 'Split Set' stabilizers
- 'Swellex' dowels
- Cable Bolts
I would advise to go to these two EduMine courses - Reinforcement Design for Excavation in Rock and Practical Rock Engineering 5 - Excavation and Support for a detailed knowledge on the application, design, installation and cost of different rock support elements. Rocscience.com also provides a good amount of information on rock supports. One of its papers can be downloaded through this link.
A mechanized mine currently uses either or all of these three types of roof bolters:
1. Rock Bolting Rigs
A variety of rock bolting rigs are available in the market with Sandvik and Atlas Copco as the two major dealers in the market, with bolt length usually varying from 5 ft to 20 ft. InfoMine Suppliers database provide a good list of suppliers providing new and used rock bolters. RTM Equipments and Hardrock Equipment Australia are among others selling/renting used rock bolting rigs. You can also search EquipmentMine for all mining equipments available for sell or rent.
2. Cable bolting Rigs
Atlas Copco Cabletec LC and Sandvik DS421 are among the two high performance one man operated mechanized cable bolting rigs that delivers long term reinforcement solution to underground mines, both providing a maximum cable length of 25 m.
3. Hand held equipments with utility equipments like scissor Lift
Hand held rock drills are used for rock bolting in areas inaccessible to mechanized rock bolting, in rock bolt repairs and in mines practicing non-mechanized mining methods. The most common use in a mechanized mine is where a fewer rock bolt installations is required or where a replacement bolt is required to install in place of a damaged roof supports. Scissor Lift is usually used to assist rock bolting at elevated areas and on roofs.
Apart from Sandvik, Changsha Enyu Engineering Equipment Co. Ltd., International Rollforms Inc., etc. are among the few suppliers in this area.
Rock drill on a Scissor Lift, heavyequipment.com
In Canada, Maclean Engineering is a common provider of roof support and other mining support equipments.
SPECIFICS - SHOTCRETE
For many applications, pneumatically applied concrete (or "shotcrete" as it is commonly referred to) is especially cost effective. It is defined in Wikipedia
or concrete conveyed through a hose and pneumatically
projected at high velocity onto a surface. Shotcrete undergoes placement and compaction at the same time due to the force with which it is projected from the nozzle. It can be impacted onto any type or shape of surface, including vertical or overhead areas. It also commonly includes coarse aggregate (up to 2 cm).
has many publications with an emphasis on safety.
Many more publications on the theory, science, and practice of mine roof support are in the InfoMine Library. The earliest and still worth the time is The Support of the Roof in the Roadway - Training Manual No. 5. As with so many of the older publications on mining practice, it is written in an easy-to-assimilate style that seems to have gone out of style.
Try http://books.google.com/ with keywords "mine roof support" for nearly 1,000 references to books that provide relevant information. Most are conference proceedings and publications of the U.S. government. Again the earliest is the Mining Engineer's Handbook from 1941.
International Rollforms, Inc. supplies Split SetŪ friction rock bolts for mining and ground support. Miners use them for mine roof bolting and mine roof support as well as to pin mesh, hang conveyors, hold pipes, and cables, secure rails in place, and for other needs.
For a "one-stop" shopping site, go no further than the Dywidag-Systems International site. Here you will find figures, diagrams, and specifications for every type of roof support product, from friction stabilizers, through cable bolts, extension bolt, fiberglass bolts, and rebar rock bolts to mesh and plates. If you had any doubts about the meaning of the multiplicity of terms used to hold up the roof of a mine, they have a brochure for each product where you can find even more information.
The company appears to have grown since 2004 by purchase of other suppliers including operations in Canada, the United States, Mexico, and Australia. And now they can rightly claim: "DSI is global market leader in the development, production and application of mining products.
Keeping in line with its strategy "Local Presence - Global Competence" DSI has over 1,300 employees worldwide with operations across Europe, Africa, Asia-Pacific and the Americas."
The site is beautiful and one can spend hours browsing through the international sites. I particularly liked the site with this picture on the "front page". I wish I could get a huge version to hang on a wall at home, but the others are almost as good and worth an art-walk tour.
Most consultants that specialize in underground rock mechanics will help you with roof support problems including the design of appropriate roof support systems. Rocscience
is one; there are twenty more listed in the InfoMine Consultants
from Rocscience appears to be the way to go to analyze the function of the Split Set
Also on the topic of roof bolts in coal mines, here are some additional resources:
EduMine as always has a fine collection of prose on roof support. Not in one place, but spread through a number of courses. You can use the EduMine search engine
to find them all, but here are my favorites:
Two key papers from the SME Conference in St Louis in 2006. The first also is published in the January 2007 issue of Mining Engineering.
- Assessing Roof fall Hazards for Underground Stone Mines: A Proposed Methodology. Iannacchione and colleagues from NIOSH in Pittsburg examined over fifty mines in the US in order to compile their Roof Fall Risk Index (RFRI). This index is intended to help quantify the risk of roof falls, hence fatalities, in the underground limestone mines of the eastern US. The authors combine ten categories of observable characteristics including geologic, mining-induced response, roof profile, and moisture factors to formulate the RFRI. The list of characteristic to consider in compiling a RFRI is as good a checklist as any to aid in observing and judging potential roof performance.
- Estimation of Roof Strata Strength in Mine Rock Geology Information System (MRGIS). Sasoaka et al from West Virginia University correlate drilling characteristics to the strength of the roof of coal mines. They define the MRGIS as a numerical quantification of the parameters that characterize normal roof bolt installation drilling: namely feed pressure, penetration rate, and rotation rate.
SPECIFIC SHOTCRETING CASE HISTORIES
Dywidag at Ekati
Drummond Mine, Ireland
SHOTCRETING SHORT JOURNAL ARTICLES
Shotcrete leads advances in ground support
Research into shotcrete applications
An Introduction to Shotcreting
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