Elasto-plastic Analysis of Circular Tunnels in Jointed Rock Masses Satisfy the Hoek-Brown Failure Criterion

The relationship between the Hoek-Brown parameters and the mechanical response of circular tunnels is illustrated. Closed-form and approximate solutions are given for the extent of the plastic zone and the stress and displacement fields under axisymmetrical and asymmetric stress conditions. For the same rock masses and under axisymmetrical stress conditions, the radius of the plastic zone in terms of Hoek-Brown criterion is generally an approximation of the radius in terms of the Mohr-Coulomb criterion. The radius in terms of the Hoek-Brown criterion is larger under low stress conditions. For poor quality rock masses (GSI < 25), measures (such as grouting, setting rock bolts, etc.) that improve the GSI of rock masses are effective in improving the stability of tunnels. It is not advisable to improve the stability of the tunnels by providing a small support resistance p through shotcrete, except for very poor quality jointed rock masses. Without reference to the quality of the rock mass, the disturbance factor D should not less than 0.5. Measures which disturb rock masses during tunnel construction should be taken carefully when the tunnel depth increases.