Consider a horizontal, rectangular opening that is 10 ft high and 20 ft wide and driven due north 5,000 ft. Rock properties are, Co = 23,700 psi, To = 1,480 psi, E = 5.29(106 psi), ν = 0.27, γ = 162pcf. The premining stress state relative to compass coordinates is: SE = 350 + 0.2 h, SN = 420 + 0.35 h, SV = 1.12 h, where stresses are in psi, h =depth in ft, E, N, V refer to compass coordinates (x = east, y = north, z = up) and compression is positive. Premining shear stresses are nil relative to compass coordinates. How wide can this opening be made before failure occurs at a depth of 1,750 ft? Justify.