A rectangular shaft 3.7 × 7.4 m is planned for deepening from a depth of 975 to 1,463 m in ground where the pre-shaft stress state relative to compass coordinates (x = east, y = north, z = up) is given (in kPa) by Sxx = 13,793 + 24.9d, Syy = 345 + 20.4d, Szz = 26.0d, Txy = −2,414 − 6.8d, Tyz = 0.0, Tzx = 0.0, where compression is positive and d is depth in m below surface.

(a) Find the best orientation of the shaft at a planned 1,175 m deep shaft station and show by sketch.

(b) Also show on the sketch where the peak stress concentrations are likely to occur.

(c) Finally, estimate the peak stress concentrations.