A longwall mine is planned in Illinois. The following data are given to you.
Mining depth- 1000 feet
Thickness of near surface weak overburden- 85 feet
Seam thickness- 6.5 feet
Panel width- 1250 feet
Unit weight of weak rock overburden- 135 pcf
Unit weight of competent overburden — 155 pcf
Average angle of draw for weak overburden- 43 degrees
Average angle of draw for competent overburden- 21 degrees
Size of the shaft- 26 feet diameter
Estimated area to be protected around the shaft on the surface- 270 ft x 130 ft
Seam is assumed to be relatively flat.
You have been asked to develop the following longwall mining related and subsidence related information for permitting.
Size of equal size pillars for development entries.
Pillar sizes for bleeder entries assuming that the first pillar adjacent to the set-up rooms is 1.25 times larger than the 2nd pillar adjacent to the first pillar. The second and third pillars are of equal size.
Assume abutment angle of 21 degrees.
Average 4-inch coal cubes strength- 3,000 psi.
USE ALPS software model for this design.
Make appropriate assumptions and justify them.
Size of protective pillar to protect the shaft and surrounding areas. Show all calculations and the shape of the protective pillar.
Width of the critical area.
Develop vertical subsidence, across the longwall panel using the NCB method.
Develop slope and curvature and horizontal strain profiles and comment on where the damage is most likely to occur.
Make appropriate comments on your developed data.
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