A rectangular shaft 18 ft by 24 ft is planned for a depth of 4,800 ft where the premining stresses relative to compass coordinates (x = east, y = north, z = up) are given by: σxx = 250 + 0.5h, σyy = 800 + 0.2h, σzz = 1.1h, where h is depth and compression is positive. Find the best shaft orientation (explain), then determine if shaft wall support is needed at some depth. Wall rock properties are: E = 6.2 million psi, ν = 0.33, c (cohesion) = 5,600 psi, φ = 52◦, γ = 158pcf.