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.
Longwall Mining:
- 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.
Subsidence Related
- 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.