A thick seam of coal is mined from the floor to a height of 13 ft at

Question:

A thick seam of coal is mined from the floor to a height of 13 ft at a depth of 1450 ft. Entry width is 21 ft and overburden averages 144pcf. Crosscuts are 18 ft wide and driven on 100 ft centers. Pillar length is three times pillar width. With reference to the stratigraphic column in the sketch and the rock properties given in Table 6.2, determine

(a) The maximum safe extraction ratio, and

(b) Pillar dimensions for a pillar safety factor of 1.5. Show solution is a carefully labeled plan view sketch stratigraphicsequence.