Question: A thin low metallurgical coal seam 3 ft thick is mined at a depth of 980 ft. The main entries are mined 4 ft into

A thin "low" metallurgical coal seam 3 ft thick is mined at a depth of 980 ft. The main entries are mined 4 ft into the R1 roof stratum to give sufficient clearance for track haulage. With reference to the stratigraphic column in the sketch and the rock properties given in Table 5.7, find:

(a) The safety factor with respect to tension of the immediate roof layer and

(b) The layer above, then

(c) Specify a reasonable bolting plan using the dead weight load approach. Include (i) bolt length, (ii) nominal diameter, (iii) steel grade, and (iv) spacing, Note: Entry width is 20 ft and overburden averages144pcf.

Rock E 106 psi y-pef (kNim) Co-psi (MPa) To-psi (MPa) (GPa) (-)

Rock E 106 psi y-pef (kNim) Co-psi (MPa) To-psi (MPa) (GPa) (-) (m) type 12.6 (86.9) 0. 19 12.7 (87.6) 0.21 5.4 (37.2) 0.23 6.3 (43.4) 0.31 12.6 (86.9) 0.19 0.75 (5.2) 0.27 12.3 (84.8) 0. 18 0.33 R5 12,700 (87.6) 14,200 (97.9) 7,980 (55.0) 8,450 (58.3) 12,700 (87.6) 3,750 (25.9) 11,500 (79.3) 13,700 (94.5) 1,270 (8.8) 1.34 (9.2) 610 (4.2) 760 (5.2) 1,270 (8.8) 425 (2.9) 1,050 (7.2) 1,260 (8.7) 160 (25.3) 158 (25.0) 152 (23.1) 146 (24.7) 156 (24.7) 92 (14.6) 155 (24.5) 160 (25.3) 21.5 (6.55) 15.2 (4.63) 1.0 (0.30) 1.5 (0.46) 6.0 (1.83) 3.0 (0.91) 10.3 (3.14) 13.0 (3.96) R4 R3 R2 RI SI FI F2 8.1 (55.9) Surface (not to scale) R5 mudstone overburden R4 sandstone R3 laminated shale R2 laminated sandstone RI (roof) sandstone SI (seam - coal) FI (floor) shale F2 limestone Stratigraphic sequence for Problem

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