The annual global meeting of the minds about the literal foundations of mining, ground control, has again adjourned. Like the many years before it, the International Conference on Ground Control (ICGCM) was again a barometer of both today’s most significant industry concerns as well as what the future holds.
Longtime chairpersons and organizers Gerry Finfinger of the National Institute for Occupational Safety and Health (NIOSH)(retired), Orica/Minova’s Steve Tadolini, West Virginia University (WVU) educator Syd Peng and NIOSH’s Tom Barczak (retired) recently told Coal Age that the annual Morgantown, West Virginia, event attracted an impressive cross-section for its 34th convening. Of the 240 total guests, seven international countries were represented by 34.
Of the many papers submitted for consideration in this year’s ICGCM, 57 were selected to be published in the meeting’s proceedings. Of those, 48 were presented by their authors.
The conference enjoyed a notable turnout from mining engineering students specializing in ground control and other disciplines; in addition to 35 professors registered, 42 students also made up the audience.
THE BEST OF THE BEST
After careful thought and consideration, the ICGCM committee selected a group of six papers it has called “Best of Ground Control.” In addition to each paper’s presentation at ICGCM 2015, the collection will be offered in the ground control technical sessions of the 2016 Society for Mining, Metallurgy and Exploration (SME) Annual Meeting and Expo next February in Phoenix.
The selected papers include “Void Fill Techniques for Stabilizing Roof Conditions During Longwall Recovery” by Robin Oldham of GMS Mine Repair and Maintenance along with Craig Dickerson and Rusty McHenry of CONSOL Energy; “Evaluating the Risk of Coal Bursts in Underground Coal Mines” by the Mine Safety and Health Administration’s Christopher Mark and Michael Gauna of the Pittsburgh Safety and Health Technology Center; “Energy Concepts in the Analysis of Unstable Coal Pillar Failure,” research by Eric Poeck, Kun Zhang, Ryan Garvey and Ugur Ozbay from the Colorado School of Mines; “Dynamic Failure in Coal Seams: Implications of Coal Composition for Bump Susceptibility” from the NIOSH Office of Mine Safety and Health Research’s Heather Lawson as well as Andrew Weakley of the University of Idaho and Arthur Miller of NIOSH.
Also included in the “Best of Ground Control” group is “A Case Study of Multiseam Coal Mine Entry Stability Analysis Using the Strength Reduction Method” by Ihsan Berk Tulu, Gabriel S. Esterhuizen, Ted Klemetti and Michael M. Murphy from the NIOSH Office of Mine Safety and Health Research in Pittsburgh along with James Sumner and Michael Sloan of Loan Mountain Processing; and “Analysis of Roof and Pillar Failure Associated With Weak Floor at a Limestone Mine” from NIOSH’s Michael Murphy, Gabriel Esterhuizen and John Ellenberger with Tim Miller from East Fairfield Coal Co. in Ohio.
Details on the time and order of appearance at SME 2016 is still being organized. The event itself, which includes sessions as well as a large exhibitor hall and networking opportunities, has been scheduled for February 21-24 at the Phoenix Convention Center.
CREATING A BUZZ AT ICGCM
Finfinger and the fellow co-chairs noted two papers in particular that seemed to return the most feedback from attendees as well as comments and additional questions.
“Each of the presenters did an exceptional job of presenting the highlights from their published papers, and the information contained within the papers is worthy of being highlighted for those interested in ground control in underground mines,” Finfinger said.
“Ihsan Berk Tulu did a noteworthy effort in presenting the engineering concept of using the strength reduction method for entry stability analysis of multiple seam mining environments. This approach has been recently pioneered by the ground control researchers at NIOSH, and the paper was prepared by Ihsan Berk Tulu, Gabriel (Essie) Esterhuizen, Ted Klemetti, Michael Murphy (all of NIOSH) along with James Sumner and Michael Sloan of Lone Mountain Processing.”
Another much-talked-about presentation was Peng’s “Research Visions for Ground Control,” which identified several areas of mine ground control worthy of further research and study. Some of these specific topics include mine geology (perhaps the most important, according to Finfinger), rock characterizations, overburden disturbances, computer modeling, stress measurements, research methodologies, a number of support topics including roof bolting, coal pillars and shield supports, and ground movement considerations.
“The importance of these topics is evident since they are routinely covered at each year’s ground control conference,” he said. “While progress has been made in each area, there is still considerable work to be done.”
Another paper of particular note, from the perspective of the chairpersons, included Eric Poeck’s presentation on “Energy Concepts in the Analysis of Unstable Coal Pillar Failures,” which Finfinger called “an interesting and fascinating discussion” of research performed using back analysis of a previous mine collapse. “Consideration of the properties of the coal and the interface conditions of the coal and rock interface was nicely handled and the resultant energy releases from the mine failures were interesting and stimulating,” he said.
“Overall, the quality of the presentations and publications was exceptional at this year’s conference and is a good sign for the next year’s event.”
SHARING EXPERIENCES
Mine case studies and operator experiences was one of the most insightful sessions of ICGCM 2015, each describing real field issues and solutions from across the globe. The first, by Strata Control Technology and Whitehaven Coal in Australia, was entitled “Measurements of Horizontal Shear Movements Ahead of Longwall Mining and Implications for Overburden Behavior.”
The group shared the details of an underground coal mine in New South Wales that had been associated with significant periodic weighting events on the longwall face. Part of the probe to better understand the causes of periodic weighting included the pre-mining installation of inclinometers capable of measuring horizontal shear movements through the full section of the overburden strata in two locations about 1 kilometer apart; the inclinometers were monitored as the longwall approached each site.
The paper presented the details of the installation, the results of the inclinometer monitoring at both sites, and the insights that these measurements provide for overburden behavior about longwall panels.
Another, “In-Situ Stress Measurement and Stress Change Monitoring in a Longwall Ming to Monitor Overburden Caving Behavior and to Design a Hydraulic Fracture Treatment Program,” was presented by Strata Control Technology of Australia as well as CSIRO Energy of Melbourne. It focused on a New South Wales longwall mine examining a strategy to use hydraulic fracturing to manage potential windblast and periodic caving hazards associated with the mine’s conglomerate strata. The researchers measured the in-situ stresses with ANZI strain cells and the overcoring method of stress relief.
In the group’s work, changes in stress associated with abutment loading and placement of hydraulic fractures were also measured using ANZI strain cells installed from the surface and from underground; it presented the results of its measurements as well as the stress change monitoring it conducted as part of the hydraulic fracturing program.
“Overcore stress measurements have indicated the vertical stress is the lowest principal stress so that hydraulic fractures placed ahead of mining form horizontally and so provide effective pre-conditioning to promote caving of the conglomerate strata,” the paper authors noted. “Monitoring of the full-scale hydraulic fractures has confirmed the hydraulic fractures grow horizontally.”
Back on U.S. shores, researchers from the University of Kentucky and Alliance Resource Partners presented “Floor Heave Control Outby the Seal Line in the No. 11 West Kentucky Seam,” describing a project at one of the operator’s complexes where floor heave had overridden seals installed in two mined-out panels. According to the paper, a third seal location was planned that would isolate that area from the mains, and a plan of support was developed to prevent future issues outby, including heave.
The research and ground control measures, which also included a mitigation ground control system application and first-stage numerical modeling, were successful; an attempt of a 3-D numerical modeling was also made.
Representatives from the Central Mining Institute in Poland shared their experiences on the other side of the pond in “Underground Measurement of Gateroad Stability at [a] Depth Around 1,000 Meters.” That work focused on Carboniferous coal measures, which is mined across Europe, including the major European underground coal mining countries of Poland, the U.K., Germany and Czech Republic, and suffers from increasing extraction depth. As a result, many have major geomechanics problems associated with ground control and support design.
“With production being concentrated into ever fewer high-performance longwalls, located at greater and greater depth, pressure to ensure the roadways’ functionality (required dimensions) continues to increase,” the group noted.
“Mining in deeper and more highly stressed mining environments creates several problems. The high stress and deterioration in geological and mining conditions, in many cases, causes problems with gateroads maintenance due to excess convergence [and] that leads to costly production gaps, longwall slowing, transport problems, an increase in the methane hazard, and in the general health and safety of the workforce, and deterioration in climatic conditions with major economic risk associated with interruption of the revenue stream.”
The work, performed at a longwall panel with roof caving within the Upper Silesian Coal Basin in Poland, showed in part via measurements that gateroad fractures in roof strata began at the mine to occur at the distance of about 1,000 m ahead of the face, and also that the load on support and gateroad convergence increased as the longwall face got closer.
“It is very important for coal mining research institutes and mine operators to investigate and develop practical solutions and apply innovative support technologies at a great depth (particularly for reinforcement and stabilization of roadways and other openings),” the researchers said in the report. “Underground measurements of stability conditions around the gateroad is of great importance to [the] mining practice, especially in planning and designing supports for longwall gateroads.”
A Pennsylvania operator, Rosebud Mining, compiled its project work in multiple-seam mining into a white paper entitled “Multiple-seam Mining in the United States: An Analysis of Multiple-seam Stability in Northern Appalachian Coal Mines with Minimal Depth of Cover and Interburden.” The project’s engineer notated the mission and findings along with some vital points on the topic.
“Currently, coal mining in the United States has progressed to the point that a growing number of mining companies are operating in coal seams located above, below and/or adjacent to previously mined-out coal seams,” Michael Castner noted. “As a result, the state and federal governments are enacting higher safety standards on mining operations. For example, in years past, pillars may have been properly designed to handle single-seam interactions for a particular mine or mines; however, today, where mining is now being considered above or below a previously mined area, these loading conditions may not be adequate to handle the removal of additional seams above or below the previously mined reserve.”
Rosebud Mining Co., headquartered in Kittanning, Pennsylvania, and Western Allegheny Energy have a combined 23 actively producing underground mining operations and at least four new mines under or ready for development. All are located in Northern Appalachia coal seams including the Upper and Lower Freeport and Upper, Middle, and Lower Kittanning seams in Pennsylvania and Ohio. At this time, more than half have multiple-seam interactions.
“Seven mines are undermining previously mined-out coal seams, and five mines are overmining previously mined-out coal seams,” he noted. “Also, between these companies, five mines have inner-seam sloping possibilities (two completed, three planned), most of which will result in mining over or under previously mined areas.
Because Rosebud’s position is not unique, it is increasingly popular by mining operators to spend an increasingly higher level of time and resources on understanding multiple-seam mining implementation, as well as the effects that previously mined-out seams have on current and future mining operations.
Enter AMSS, or NIOSH’s Analysis of Multiple-seam Stability software program, that was first developed by agency researcher Chris Mark.
“Thus, the best possible engineering calculations and designs are imperative to assist in ensuring the safety of the mining operation and the miners, while still allowing for the extraction of other coal reserves,” the Rosebud engineer said. “Fortunately, while multiple-seam interactions cannot always be avoided, they do not always produce catastrophic results; when properly anticipated and designed for, multiple-seam interactions can be identified and occur without threatening the safety of miners or otherwise disrupting mining operations. The key is to identify the high-risk multiple-seam interactions [and then make a] decision to avoid these areas or to engineer safe development.”
The final paper in the operational and mine case study session was also one selected for SME 2016: “Analysis of Roof and Pillar Failure Associated with Weak Floor at a Limestone Mine” by members of the NIOSH ground control team and East Fairfield Coal Co. in eastern Ohio.
The group’s work focused on a limestone mine in Ohio that had instability problems that led to massive roof falls extending to the surface. Specifically, the researchers examined how weak, moisture-sensitive floor had an impact on instability issues.
As the report noted, previous NIOSH research on the topic had not touched on any analyses for weak floor or weak bands; in fact, the agency recommended that when such issues would arise they should be investigated further using a more advanced analysis.
The International Conference on Ground Control in Mining will return to West Virginia for its 35th event July 26-28, 2016. A call for papers will be released later this year.
