Laboratory tests on core from exploration drilling show that

Co = 148.3 MPa, To = 10.55 MPa, E = 43.10GPa,

G = 17.24GPa, γ = 22.78kN/m3, while premining stress measurements can be fit to the formulas

SE = 1,379 + 6.8h, SN = 4,138 + 20.4h, SV = 24.9h 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 3.7 × 7.4m rectangular shaft is selected and for some reason is oriented with the long axis N30W. Find the resulting factors of safety at 655 m.