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Ground stress in mining (part 2) : calibrating and verifying longwall stress models
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January 2020
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Description:"Researchers from the National Institute for Occupational Safety and Health (NIOSH) have been conducting ground control research with the goal of improving the stability of mine excavations to ensure the safety of mine workers. Numerical models are used to evaluate mine layout design to establish better procedures for predicting ground stress in mining to identify safe and unsafe working areas and escapeways. Current published guidance by the Mine Safety and Health Administration (MSHA) recommends an approach to calibrating models to observations, but it does not include recommendations for using in situ measurements to calibrate such models. A specific goal of this research is to explore and demonstrate procedures for calibrating numerical models to both observations and measurements. In cooperation with two mining companies in the western United States, NIOSH researchers compiled large data sets of measurements and observations during mining. The purpose of these case studies was to determine ways to calibrate and verify models constructed with various modeling tools to measurements and observations, evaluate pillar strength formulas for applicability, identify deficiencies in the model calibration process, and recommend procedures for calibrating models so that longwall gate road design is improved and the margin between safe and unsafe designs is more clear. The data sets from these two mines were described in Part 1, Larson et al. [NIOSH 2020] (herein referred to as Ground Stress in Mining Part 1), of this two-part series of reports. Also in Part 1, a procedure was recommended to detect first arrival of mining-induced abutment stress ahead of the face with various instruments and with an observational survey of ground conditions. Taking such measurements is critical in the model calibration process. In this report (Part 2), observations of floor heave and no floor heave were used to determine the general range of strength properties of the floors of the mine's gate roads. Measurements of first arrival of mining-induced abutment stress were converted to equivalent side load transfer distances for use in calibrating models. Load transfer distance at Mine A was four times the result calculated with the empirical Peng and Chiang equation. The load transfer distance at Mine B could not be determined with the same precision, but its probable range is consistent with the load transfer distance measured at Mine A. Calibration of rock mass stiffness or of stratigraphic moduli of elasticity was possible in these case studies using equivalent load transfer distance. However, for the boundary element code LaModel, a displacement-discontinuity program used in this analysis, the rock mass stiffness was so great that it was impossible to calibrate final gob stiffness and achieve reasonable gob loading." - NIOSHTIC-2
NIOSHTIC no. 20058392
Suggested citation: NIOSH [2020]. Ground stress in mining (part 2): calibrating and verifying longwall stress models. By Larson MK, Tesarik DR, Johnson JC. WA: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2020-104. https://doi.org/10.26616/NIOSHPUB2020104.
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DOI:10.26616/NIOSHPUB2020104
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