ICGCM Papers:
Fundamental Research Studies
 
 
Unanticipated Multiple Seam Stresses From Pillar Systems Behaving As Pseudo Gob - Case Histories
35th International Conference on Ground Control in Mining
Unanticipated Multiple Seam Stresses From Pillar Systems Behaving As Pseudo Gob - Case Histories
by
Michael Gauna, MSHA, Pittsburgh Safety and Health Technology Center, Triadelphia, United StatesChristopher Mark, MSHA, Pittsburgh Safety and Health Technology Center, Pittsburgh, United States
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[Conference] 35th International Conference on Ground Control in Mining
[Price] Free  [Comments] 0
[Topical Area] Fundamental Research Studies
[Author] Michael Gauna, MSHA, Pittsburgh Safety and Health Technology Center, Triadelphia, United StatesChristopher Mark, MSHA, Pittsburgh Safety and Health Technology Center, Pittsburgh, United States
[Abstract] 
Key Conclusions:
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Miners must recognize that multiple seam stress can be encountered from overlying or underlying old workings where an inspection of the old workings maps indicates that interaction stresses are not expected. Mining operations must exercise vigilance and immediately react when evidence of such stresses are encountered. The paper provides guidance so when an operation encounters pseudo gob stress interaction the hazard can be mitigated.
Key Findings:
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Case studies discussed include: • Pillar rib degradation at a West Virginia mine at 1100-foot depth that contributed to a rib roll fatality. • Pillar rib deterioration at a Western Kentucky mine at 570-foot depths that requires pillar size adjustment and installation of supplemental bolting. • Roof deterioration at an eastern Kentucky mine at 1300-foot depth that stopped mine advance and required redirecting the section development. • Coal burst on development at an eastern Kentucky mine at 1700-foot depth that had no nearby pillar recovery. • Coal burst on development at a West Virginia mine at the relatively shallow depth of 1100 feet that also had no nearby pillar recovery
Objective of the Paper:
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The paper presents a number of case histories that illustrate pseudo gob phenomenon with discussion of the mitigation methods available.
Problem Statement:
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Underground coal mining in the U.S. has regions with previous workings above and/or below an actively mined seam. Miners know that overlying or underlying fully extracted coal areas, also known as gob regions, can result in abutment stresses that affect the active mining. If there was no full extraction, and the past mining consists entirely of intact pillars, the stresses on the active seam are usually minimal. However, experience has shown that in some situations there has been sufficient yielding in overlying or underlying pillar systems to cause significant stress transfer to the active workings. In other words, the overlying or underlying pillar system behaves as a “pseudo gob.” The presence of a pseudo gob is often unexpected, and the consequences can be severe.