Laboratory tests on core from exploration drilling show that

Co = 21,500 psi, To = 1,530, E = 6.25(106) psi,

G = 2.5(106) psi, γ = 144pcf, while premining stress measurements can be fit to the formulas SE = 200 + 0.3h, SN = 600 + 0.9h, SV = 1.1h, where E,N, V refer to compass coordinates (x=east, y=north, z =up), stress is in kPa, depth h is in m, and compression is positive.

Premining shear stresses are nil relative to compass coordinates. Suppose a rectangular a 12 × 24 ft rectangular shaft is selected and for some reason is oriented with the long axis N30W. Find the resulting factors of safety at 2,150 ft.