With reference to Problem 9, determine the maximum possible roof span, given that all roof rock must have a safety factor greater thanone.

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To (102) psi (MPa) Co (103, psi (MPa) E (106) psi (GPa) Rock type Unit y-pef (kN/m) h-ft (m) v(-) 11.2 (77.2) 6.0 (41.4) 0.35 (2.4) 7.5 (51.7) 155 (24.5) 138 (21.8) 2.5 (17.2) 0.20 90 (14.2) 0.35 (2.4) 0.31 142 (22.5) Sandstone Shale Coal Laminated sandstone Shale Coal Sandstone R5 R4 R3 4.7 (32.4) 0.25 10.3 (7.1) 4.0 (2.8) 0.25 (0.2) 6.2 (4.3) 8.9 (2.71) 3.6 (1.10) 0.5 (0.15) 2.5 (0.76) R2 3.1 (21.4) 0.18 6.0 (41.4) 4.0 (2.8) 0.35 (2.4) 0.25 (0.2) 11.2 (77.2) 10.3 (7.1) 13.1 (90.3) 15.2 (10.5) 1.5 (0.46) 16.8 (5.12) 4.7 (1.43) 7.9 (2.41) RI 138 (21.8) 2.5 (17.2) 0.2 90 (14.2) 0.35 (2.4) 0.31 155 (24.5) 4.7 (32.4) 0.25 148 (23.4) 6.0 (41.4) 0.21 Seam FI F2 Claystone