A thick seam of coal is mined from the floor to a height of 13 ft at a depth of 1,450 ft. With reference to the stratigraphic column in the sketch and the rock properties given in Table 5.2, assume L=21 ft, then find:

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

(b) The layer above

(c) 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 21 ft and overburden averages 144pcf.

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Rock type E(106 psi) - Co (psi) y (pcf) To (psi) h (ft) R5 12.6 0.19 12,700 0.21 14,200 1,340 0.19 12,700 8,450 7,980 3,750 0.18 I1,500 1,270 160 21.5 R4 12.7 158 156 146 152 15.2 6.0 1.5 1,270 760 610 R3 12.6 6.3 5.4 0.31 R2 RI 0.23 2.0 15.0 10.3 SI FI 0.75 12.3 0.27 425 1,050 1,260 92 155 F2 8.1 0.33 13,700 160 13.0