An alternative mining plan is to develop two levels, below the upper A Level and mine only the high grade. The B Level would be in the 13.1 m of high grade, while the C level would be in the lower 6.10 m of high grade in the 31.1 m column shown in the detailed geologic column. Determine the maximum possible roof span for the BLevel.

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h ft (m) Co psi (MPa) To psi (MPa) Property stratum E 10°psi G 10ʻpsi (GPa) y pef (kNim) (GPa) Limestone (R5) Coal (R4) Mudstone (R3) Sandy shale (R2) Shale (RI) Coal (Seam) Sandstone (FI) 152(24.0) 93 (14.7) 153 (24.2) 142 (22.5) 138 (21.8) 90 (14.2) 147 (23.3) 15.9 (4.8) 9.83 (67.8) 4.27 (29.4) 0.29 (2.0) 1.460 (10.0) 17,690 (122) 390 (2.7) 2,780 (19.2) 13,750 (94.8) 1,580 (10.9) 720 (5.0) 6,450 (44.5) 650 (4.5) 7,400 (51.0) 310 (2.1) 3,400 (23.4) 12,300 (84.8) 1,350 (9.3) 0.12 (0.8) 1.4 (0.4) 9.8 (3.0) 7.67 (52.9) 3.07 (21.2) 2.7 (0.8) 4.16 (28.7) 1.79 (12.3) 1.3 (0.4) 3.62 (25.0) 1.53 (10.6) 16.5 (5.0) 0.35 (2.4) 8.6 (2.6) 8.32 (57.4) 3.35 (23.1) 0.14 (1.0)