Improving the Understanding of Dynamic Failures and Massive Collapses in Coal Mines Using Numerical Modeling

Details

• Personal Author:
  Ozbay U
• Description:
  Events of violent rock failures in deep coal mines, which are commonly known as "bumps", pose a serious threat to the safety of mine workers. The infamous Crandall Canyon disaster in Utah in 2007 was a tragic large coal bump event that claimed nine lives. Bumps of such magnitudes are low frequency, high impact events, although smaller magnitude bumps are also a reason for concern in deep coal mines. The underlying mechanism of bump events is complex and involves "unstable" failures in excavation walls triggered by a sudden release of stored energy from the surrounding rockmass. The objective of this research is to improve the mechanistic understanding of unstable failures to develop design methodologies for protecting miners against the perils of coal bump events. This report describes the research carried out for improving the mechanistic understanding of unstable failures using numerical modeling and presents the results obtained. In addition to this report, the research outcomes are also published in three PhD theses and several technical publications in scientific journals and conference proceedings. The research makes use of the commercially available finite difference and discrete element based numerical modeling codes, namely FLAC, FLAC3D, UDEC, 3DEC, PFC, and PFC3D. In all modeling cases, the rockmass is modeled as an elastic material in the pre-failure state and as a plastic or brittle material during failure. Significant emphasis is placed on validating the ability of these models to identify failure stabilities under compressive and shear loads. The failure stability concept is based on the theory that a failure becomes unstable if the failing rock is unable to fully absorb the strain energy provided by the elastically loaded rockmass. The FLAC/3D modeling focuses on developing instability identifiers that can be used for evaluating the locations and relative magnitudes of unstable failures within a rockmass. An energy balance is introduced for calculating the excess energy released as a result of unstable equilibrium in a rockmass. The identifiers and excess energy calculations provide a generalized methodology for assessing unstable failures within potentially complex mine models. They may be applied to the design of mine layouts in bump-prone conditions or to perform backanalyses on unstable failures in select mining layouts. The UDEC modeling studies cover rock failures under compression and discontinuity shear loading conditions. Using a double shear test model, methodologies are introduced for identifying shear failure stabilities both in laboratory and in-situ scale models. The modeling results show that rock-coal interfaces may fail in a stable or unstable discontinuity shear mode depending on the post-peak characteristics of the discontinuity interface and the shear stiffness of the interface. Also shown is that unstable coal sidewall and mining face failures can occur when a sudden de-confinement is triggered by an unstable failure at the rock-coal interfaces or by the existence of weak contact regions along the interfaces. The PFC simulations focused on failure stability analyses in compression using the bonded particle and the displacement softening contact models. A mechanically coupled finite difference and discrete element model of coal is utilized to study the effect of geometry and loading system stiffness on pillar failure stability. A transition from stable to unstable failure was observed when the loading system stiffness was less than the post-peak stiffness of the coal. Stiffness measurements showed unstable and stable failures by assigning different moduli to the loading system. Damping work in PFC simulations appears particularly useful as a failure indicator as it is observed to be consistently higher during unstable failures. The results reveal shortcomings in the bonded particle model and promote the displacement-softening contact model for continued studies of rock failure stabilities. [Description provided by NIOSH]
• Subjects:
  Coal Coal Mining Mining Occupational Health Safety
• Keywords:
  Coal Miners Coal Mining Failure Analysis Mining Industry Models Rock Falls Rock Mechanics
• Series:
  Grant Final Reports
• Publisher:
  National Institute for Occupational Safety and Health
• Document Type:
  Text
• Funding:
  Grant
• Genre:
  Final Grant Report
• Place as Subject:
  Colorado ; OSHA Region 8
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Division:
  OEP - Office of Extramural Programs
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  1-93
• NIOSHTIC Number:
  nn:20056875
• NTIS Accession Number:
  PB2019-101419
• Citation:
  Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, R01-OH-009764, 2013 Nov; :1-93
• Contact Point Address:
  Ugur Ozbay, Ph.D., Pr. Eng., Professor of Mining Engineering, Colorado School of Mines, 1500 Illinois Street, Golden, Colorado 90401
• Email:
  mozbay@mines.edu
• Federal Fiscal Year:
  2014
• NORA Priority Area:
  Mining
• Performing Organization:
  Colorado School of Mines, Golden, Colorado
• Peer Reviewed:
  False
• Start Date:
  20090901
• Source Full Name:
  National Institute for Occupational Safety and Health
• End Date:
  20130831
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:ba76f6bf0c38c6ad4859cda93b971656a89b40832e4e0acbd5d33abec87b3a4e84794b99158f3a4f1839a05a1e8564553f6f0515a3b4b47f487a8cf2feed5a88
• Download URL:
  https://stacks.cdc.gov/view/cdc/218916/cdc_218916_DS1.pdf
• File Type:
  [PDF - 2.71 MB ]