Design of Mine Excavations

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 2^nd 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.