Question: With reference to the strata data given in the sketch and Table 5.4, seam depth is 1,324 ft (404 m), strata dip is negligible and

With reference to the strata data given in the sketch and Table 5.4, seam depth is 1,324 ft (404 m), strata dip is negligible and entries are planned 21 ft (6.4 m) wide. Mining height from the sandstone floor is 15 ft (4.6 m).

1. Determine the immediate roof safety factor.

2. Determine bolting pressure needed to reduce sag of all roof layers to zero, assuming bolts are anchored in R3 and the sag of R3 is negligible.

3. Layout a bolting pattern based on dead weight load basis and specify bolt length, diameter, steel grade, spacing, and bolt safety factor using R3 as an anchor stratum.

4. What is the immediate roof safety factor after bolting according to dead weight load design?

5. Explain how gas pressure above the roof shale would affect calculation of the safety factor of R1 beforebolting.

Co (103) psi (MPa) To (103) psi (MPa) E (106) psi (GPa)

Co (103) psi (MPa) To (103) psi (MPa) E (106) psi (GPa) y (pcf) (kN/m) Rock type h-ft (m) 4.5 (31.0) 0.25 16.0 (I10) 2.7 (18.6) 0.19 3.1 (21.4) 0.20 0.35 (2.4) 0.30 3.5 (24.1) 0.25 R3 0.80 (5.52) 0.65 (4.48) 0.40 (2.76) 0.15 (1.03) 0.8 (5.52) 148 (23.4) 142 (22.5) 135 (21.4) 95 (15.0) 148 (23.4) 16.0 (4.9) 2.5 (0.8) 2.0 (0.6) 18.0 (5.5) 14.0 (4.3) 12.5 (86.2) 8.0 (55.2) 3.0 (20.7) 0.8 (5.5) R2 RI SI FI Surface ..overburden (not to scale) R3 sandstone R2 laminated sandstone RI shale SI coal FI sandstone

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