A thin low metallurgical coal seam 3 ft thick is mined at a depth of 980 ft.

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 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.