heather e. lawson jeffrey k. whyatt mark k. larson
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Analysis of Potential Implications of Observed Load Transfer Distance and Abutment Angle on Longwall Pillar Loading. Heather E. Lawson Jeffrey K. Whyatt Mark K. Larson. Background. LTD 4x greater than expected at Elk Creek Mine β=21° (H (ft)/900) -1.59 at depths between 900 ft and 2050 ft. - PowerPoint PPT PresentationTRANSCRIPT
Analysis of Potential Implications of Observed Load Transfer Distance and Abutment Angle on Longwall Pillar Loading
Heather E. LawsonJeffrey K. WhyattMark K. Larson
Background• LTD 4x greater than expected at
Elk Creek Mine• β=21° (H (ft)/900)-1.59 at depths
between 900 ft and 2050 ft
Objective: Establish which regional ground characteristics have the most impact on pillar loading
Background• ALPS pillar loading equations;
simple and useful• R=1-((D-W)/D)3 where D is load
transfer distance
Disclaimer: Substitution into ALPS software is not recommended
Background• Ls=H2(tanβ)(ϒ/2), when P≥2Htanβ • Or else, Lss=((HP/2)-(P2/8tanβ))ϒ
Disclaimer: Substitution into ALPS software is not recommended
Supplemental StudyLaModel Analysis• Re-examines role of
LTD in TG loading• Indicates that LTD
influences TG loading• Suggests a modified
FT
Case StudiesSensitivity Study•Compares two scenarios:
– Shallow longwall (supercritical loading)
– Deep longwall (subcritical loading)
•Pillar loads compared to “default” and graphed
Case 1-Shallow Mine
Case 2-Deep Mine
Shallow Case Study Results• LaModel-based LT loading is most sensitive to D, • LB is next most sensitive• LH is least sensitive• Traditional LT is insensitive to changes in DDegree of sensitivity is dependent on loading condition
Standard value = 208 ft.
Shallow Case Study Results• Changes in D have little effect on smaller scale• Loading is moderately to very sensitive to small changes in βLoading is more sensitive to β than to D.
Standard value = 208 ft.
Parameter LH LB LTAbutment angle, β M* 7% M 12% V 21%
Load transfer distance, D S <1% S <1% I 0%
Deep Case Study Results• LB in Gateroad 1 is most sensitive to changes in D,• LH (also Gateroad 1) is next most sensitive, • LaModel-based LT (Gateroad 2) is the next most sensitive, and• Bleeder loading in Gateroad 2 is the least sensitive.Degree of sensitivity is still sensitive to loading condition, but is diluted by
differences in gateroad width.
Standard value = 416 ft.
Deep Case Study Results• LB in Gateroad 1 and LT in Gateroad 2 are most sensitive to changes in
β, • LB in Gateroad 2 is the next most sensitive, and• LH (Gateroad 1) is least sensitive.Degree of sensitivity is still sensitive to loading condition, and panel
criticality—more sensitive in supercritical panels
Standard value = 21°Supercritical vs. Subcritical threshold
Deep Case Study Results• LB in Gateroad 1 and LT in Gateroad 2 are most sensitive to changes in β, • LB in Gateroad 2 is the next most sensitive, and• LH (Gateroad 1) is least sensitive.Sensitivity increases by between 4%-7% below the supercritical threshold.
21°
Supercritical vs. Subcritical threshold
8°
Parameter LH LB LTAbutment angle β, centered on 21° (subcritical) M 7% M 10% M 9%
Abutment angle β, centered on 8° (supercritical), relative to 8° M 11% V 17% V 16%D, (subcritical) S <1% S <1% I 0%
Conclusions• Tailgate loading is affected by load transfer distance (D),
as modeled using LaModel• Overall, abutment angle (β) has more influence on pillar
loading than load transfer distance (D)• Changes in β have a greater effect in supercritcal panels
than subcritical panels• Relative degree of sensitivity to changes in β and D are
dependent upon gateroad function• More research is needed in western coalfields and deep
mines
Questions?Presented by: Heather LawsonContact info: 509-354-8061, [email protected] Office of Mine Safety and Health Research is a division of the National Institute for Occupational Safety and Health (NIOSH) www.cdc.gov/niosh/mining
NIOSH is a division of the Centers for Disease Control and Prevention within the Department of Health and Human Services www.hhs.gov