UNDERGROUND PERFORMANCE ASSESSMENT OF AN ENGINEERED COMPOSITE WOODEN CRIB FOR TAIL GATE ENTRY SUPPORT IN LONGWALL MINING
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Title
UNDERGROUND PERFORMANCE ASSESSMENT OF AN ENGINEERED COMPOSITE WOODEN CRIB FOR TAIL GATE ENTRY SUPPORT IN LONGWALL MINING
ICCI Project ID
DEV07-2
Investigator
Chugh
Institution
Southern Illinois University
ICCI Abstract
Coal mines typically use wooden cribs to provide standing support between roof and floor. Cribs are more extensively used in longwall mining than in room-and-pillar mining. In longwall mining, they are used primarily to support gate, set up and bleeder entries and provide temporary support during the shield removal process when moving the longwall equipment from one face to the other. A typical crib uses prismatic wooden elements of 6-inch x 6-inch x 30-inch or 6-inch x 6-inch x 36-inch, although other sizes may also be used. It is not uncommon for a typical longwall coal mine to use 400,000 to 500,000 crib elements each year at a cost of 1.5-2.0 million dollars annually.
Although cribs have been used since the inception of mining, in their current form they have the following disadvantages and/or limitations: 1) Since loading on the crib element is transverse to the wood grain, low crib stiffness leads to low load carrying capacity and large deformations, 2) The cross-section of the crib element is uniform even though most of the stress in the element is confined to a small area around contact points, thus making the element heavier, 3) The uniform cross-section also makes installation around irregular roof difficult, and 4) Handling crib elements for placement at heights above four feet requires considerable effort.
The principal investigator and the project team have developed a novel, engineered, wooden element called the ATLAS crib that overcomes most of the above disadvantages. Results of testing at the Illinois Coal Development Park in Carterville, IL and National Institute of Occupational Safety and Health (NIOSH) facilities in Pittsburgh, PA demonstrate that these crib supports can be a viable support for longwall gate entries. Product reviews from highly experienced industry professionals in Illinois have also been positive. This field demonstration project was designed to perform a side-by-side comparison of the performance of these supports with conventional cribs on an active longwall face in the Midwest. The project tasks were: 1) Establish field demonstration site, 2) Fabricate engineered crib elements for field demonstration, 3) Perform a demonstration of engineered cribs in the mine, and 4) Conduct data analysis and synthesis. This was a cooperative project between American Coal Galatia Mine, NIOSH, Illinois Clean Coal Institute (ICCI), and SIU. The goal was to develop data that would allow the industry to make informed decisions regarding use of ATLAS cribs in longwall mines. It was also hoped that such data would allow MSHA to permit the use of these supports with confidence in longwall mines throughout Illinois and the USA.
The crib demonstration was conducted on a longwall face operating at about 425 feet depth in the Herrin #6 seam. The longwall face is 1,000 feet wide and the average mining height is approximately 6.5 feet. The immediate roof strata consist of 4-6 inches of Anna Black Shale, 5.5 feet of Brereton Limestone, and about 23 feet of massive sandstone. The immediate floor strata consist of claystone and shale with up to 10 feet of claystone in some areas. Gate road development is a three-entry system with entries 80 feet apart (center-to-center or c-c) with cross-cuts at 150-foot (c-c) intervals. Supplemental supports are required in all bleeder entries and in the tailgate entry serving an active longwall face. The roof control plan requires these supplemental supports to be maintained about 200 feet ahead of the location of the longwall face. Cribs are installed as supplemental supports in two rows spaced approximately 5-6 feet apart across the entry and eight feet or less along each row. Two additional cribs are placed in each cross-cut.
The demonstration area was located roughly 500 feet inby the recovery room in the outside entry of the 1st West longwall headgate and spanned a distance of about 250 feet. The demonstration area consisted of two adjacent sections; one having conventional cribs and the other having engineered cribs. In each area of demonstration, two rows of cribs were installed. Spacing was eight feet apart along the entry and approximately five feet apart across the entry. Installation of cribs was done during the period March 21-27, 2008.
Load monitoring and convergence monitoring equipment on cribs in both areas were installed on March 26 by NIOSH and SIU personnel. Two roof-to-floor convergence monitoring stations were located in the engineered crib area and one in the conventional crib area. The following results summarize the study to date.
• The engineered cribs were planned to be manufactured by a saw mill in southern Illinois with oversight by the project team. However, due to flooding, the saw mill could not fabricate the cribs. Thus, the SIU project team fabricated all of the engineered cribs for this demonstration at the Illinois Coal Development Park.
• In addition to the cribs for this demonstration project, over 2,000 crib elements, fabricated by four saw mills in the tri-state area, have been shipped to different mines for experimental trials.
• QA/QC protocols have been developed and implemented during the manufacturing process. The results of quality assurance checks on manufactured cribs were used for process improvement and training purposes. A shipment from one saw mill was rejected when it did not meet QA/QC requirements.
• Guidelines for proper installation of engineered cribs were developed.
• Prior to installation of engineered cribs in the test area, training was provided to miners on proper installation of engineered cribs.
• The installation time for an engineered crib was typically about 25-30% less than a conventional crib.
• Significant time and cost savings accrue from engineered cribs where crib elements must be manually transported over a considerable distance to a construction site. This is because two engineered crib elements can be easily carried by a worker (one in each hand) since they are about 40% lighter.
• Site preparation for engineered cribs is much easier since only four smaller areas, equal to the size of each base, need to be prepared.
• Based on available data to date, engineered cribs are performing very similarly to conventional cribs.
• At the demonstration mine, input was sought from the Chief Engineer, longwall coordinator, section bosses, and workers carrying and installing the engineered cribs. Almost all comments received were positive.
• During the project team's last visit to the demonstration area as part of this project on July 1, 2008, the cribs seemed to be performing as well as the conventional cribs based on visual observations.
• During the project period, engineered cribs were shown to several coal company high-ranking professionals at their mines to seek their input. This was done in lieu of an advisory committee. These included Willow Lake, Wild Cat Hills, Gibson County Coal, Sunrise Mining Company, and Vermillion Grove. Again the comments received were positive.
• Overall, this demonstration study to date is considered a success. Over 2,000 crib elements have been shipped to mining companies for experimental evaluation. One mining company plans to install them in front of mine seals while another mining company has used them to support weak roof areas.
Although cribs have been used since the inception of mining, in their current form they have the following disadvantages and/or limitations: 1) Since loading on the crib element is transverse to the wood grain, low crib stiffness leads to low load carrying capacity and large deformations, 2) The cross-section of the crib element is uniform even though most of the stress in the element is confined to a small area around contact points, thus making the element heavier, 3) The uniform cross-section also makes installation around irregular roof difficult, and 4) Handling crib elements for placement at heights above four feet requires considerable effort.
The principal investigator and the project team have developed a novel, engineered, wooden element called the ATLAS crib that overcomes most of the above disadvantages. Results of testing at the Illinois Coal Development Park in Carterville, IL and National Institute of Occupational Safety and Health (NIOSH) facilities in Pittsburgh, PA demonstrate that these crib supports can be a viable support for longwall gate entries. Product reviews from highly experienced industry professionals in Illinois have also been positive. This field demonstration project was designed to perform a side-by-side comparison of the performance of these supports with conventional cribs on an active longwall face in the Midwest. The project tasks were: 1) Establish field demonstration site, 2) Fabricate engineered crib elements for field demonstration, 3) Perform a demonstration of engineered cribs in the mine, and 4) Conduct data analysis and synthesis. This was a cooperative project between American Coal Galatia Mine, NIOSH, Illinois Clean Coal Institute (ICCI), and SIU. The goal was to develop data that would allow the industry to make informed decisions regarding use of ATLAS cribs in longwall mines. It was also hoped that such data would allow MSHA to permit the use of these supports with confidence in longwall mines throughout Illinois and the USA.
The crib demonstration was conducted on a longwall face operating at about 425 feet depth in the Herrin #6 seam. The longwall face is 1,000 feet wide and the average mining height is approximately 6.5 feet. The immediate roof strata consist of 4-6 inches of Anna Black Shale, 5.5 feet of Brereton Limestone, and about 23 feet of massive sandstone. The immediate floor strata consist of claystone and shale with up to 10 feet of claystone in some areas. Gate road development is a three-entry system with entries 80 feet apart (center-to-center or c-c) with cross-cuts at 150-foot (c-c) intervals. Supplemental supports are required in all bleeder entries and in the tailgate entry serving an active longwall face. The roof control plan requires these supplemental supports to be maintained about 200 feet ahead of the location of the longwall face. Cribs are installed as supplemental supports in two rows spaced approximately 5-6 feet apart across the entry and eight feet or less along each row. Two additional cribs are placed in each cross-cut.
The demonstration area was located roughly 500 feet inby the recovery room in the outside entry of the 1st West longwall headgate and spanned a distance of about 250 feet. The demonstration area consisted of two adjacent sections; one having conventional cribs and the other having engineered cribs. In each area of demonstration, two rows of cribs were installed. Spacing was eight feet apart along the entry and approximately five feet apart across the entry. Installation of cribs was done during the period March 21-27, 2008.
Load monitoring and convergence monitoring equipment on cribs in both areas were installed on March 26 by NIOSH and SIU personnel. Two roof-to-floor convergence monitoring stations were located in the engineered crib area and one in the conventional crib area. The following results summarize the study to date.
• The engineered cribs were planned to be manufactured by a saw mill in southern Illinois with oversight by the project team. However, due to flooding, the saw mill could not fabricate the cribs. Thus, the SIU project team fabricated all of the engineered cribs for this demonstration at the Illinois Coal Development Park.
• In addition to the cribs for this demonstration project, over 2,000 crib elements, fabricated by four saw mills in the tri-state area, have been shipped to different mines for experimental trials.
• QA/QC protocols have been developed and implemented during the manufacturing process. The results of quality assurance checks on manufactured cribs were used for process improvement and training purposes. A shipment from one saw mill was rejected when it did not meet QA/QC requirements.
• Guidelines for proper installation of engineered cribs were developed.
• Prior to installation of engineered cribs in the test area, training was provided to miners on proper installation of engineered cribs.
• The installation time for an engineered crib was typically about 25-30% less than a conventional crib.
• Significant time and cost savings accrue from engineered cribs where crib elements must be manually transported over a considerable distance to a construction site. This is because two engineered crib elements can be easily carried by a worker (one in each hand) since they are about 40% lighter.
• Site preparation for engineered cribs is much easier since only four smaller areas, equal to the size of each base, need to be prepared.
• Based on available data to date, engineered cribs are performing very similarly to conventional cribs.
• At the demonstration mine, input was sought from the Chief Engineer, longwall coordinator, section bosses, and workers carrying and installing the engineered cribs. Almost all comments received were positive.
• During the project team's last visit to the demonstration area as part of this project on July 1, 2008, the cribs seemed to be performing as well as the conventional cribs based on visual observations.
• During the project period, engineered cribs were shown to several coal company high-ranking professionals at their mines to seek their input. This was done in lieu of an advisory committee. These included Willow Lake, Wild Cat Hills, Gibson County Coal, Sunrise Mining Company, and Vermillion Grove. Again the comments received were positive.
• Overall, this demonstration study to date is considered a success. Over 2,000 crib elements have been shipped to mining companies for experimental evaluation. One mining company plans to install them in front of mine seals while another mining company has used them to support weak roof areas.
Start Date
3/1/2008
End Date
8/31/2008
Year Funded
2007
Collection
Citation
“UNDERGROUND PERFORMANCE ASSESSMENT OF AN ENGINEERED COMPOSITE WOODEN CRIB FOR TAIL GATE ENTRY SUPPORT IN LONGWALL MINING,” ICCI Reports, accessed May 20, 2024, https://isgswikis.web.illinois.edu/icci_reports/items/show/21.