An in situ stress field between 914 and 1,067 m is fit to the formulas v =

An in situ stress field between 914 and 1,067 m is fit to the formulas σv = 25.45h, σH = 24,138 + 7.47h, σh = 24,138 + 7.47h, where the stresses are in kPa and the depth h is in m. Stresses σv, σH, σh are principal stresses in the vertical and horizontal directions. The weakest rock along the proposed shaft route has an unconfined compressive strength of 55.2 MPa and a tensile strength of 5.17 MPa. A circular, concrete liner is planned below 1,067 m for a shaft with an outside diameter of 5.5 m. If the liner is 0.3 m thick and the concrete properties are: E = 34.48GPa, ν = 0.20, γ = 24.7kN/m3, Co = 31.0 MPa, and To = 3.10 MPa, determine what uniform radial stress would just cause the liner to fail, assuming the concrete follows a Mohr–Coulomb criterion.