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

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 D

Degree 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 β

Loading 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, Helawson@cdc.govThe 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