Analytical study of hydraulic tunnel in brittle rock masses with strain-softening characteristic

In order to describe the strain-softening behavior after peak stress of brittle rock masses, a brittle-damage variable under uniaxial compression status is introduced in analytical solutions. On this basis, the damage variable for brittle rock mass nearby circular tunnel is derived in this paper, when the tunnel is subjected to a hydrostatic stress field. Considering the influence of seepage, analytical solutions of elastoplastic stresses and plastic radii for circular hydraulic tunnel are proposed. Moreover, the direction of first principal stress for surrounding rock nearby circular tunnel is taken into account in the derivation process: The calculation results of example show that after considering brittle damage, the plastic radius will increase to a certain extent compared with elastic-perfectly plastic model; besides, plastic radius will also rise along with growth of brittle extent for rock masses. With consideration of seepage influence, the plastic radius will expand, and elastoplastic stresses are also influenced by a series of seepage parameters. Consequently, it is non-ignorable to consider impacts of brittle characteristic for rock masses and seepage in structural stability analysis of hydraulic tunnel.