Abstract: Considering the damage characteristic of the brittle rock, the brittle damage model is introduced; and the expression of damage variable under 3-dimension isotropic damage condition is derived. The analytical solutions of elastoplastic stress and plastic radius of the circular hydraulic tunnel are deduced, considering the seepage influence, damage influence and principal stress corresponding relations under different engineering conditions. The research about brittle characteristic shows that the plastic radius of surrounding rock will increase after considering brittle damage. The more distinct the brittle characteristic is, the more larger plastic radius will be. Whether the first principal stress of rock nearby the tunnel is radial stress or tangential stress, the consideration of seepage will expand the plastic zone of the surrounding rock. In the process of internal water pressure increase from zero, the plastic radius will gradually decrease accompany with the increase of internal water pressure, until the plastic zone disappears in the end; however, when the internal water pressure exceeds the critical pressure; the plastic zone appears again; the plastic zone will gradually increase.

Key words: circular tunnel, seepage, brittle damage, elastoplastic solution