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Abstract Rocks exhibit different strain-softening and dilatancy behaviors under various confining pressures. For tunnel excavation，the method to obtain the stress and strain states considering variability of the confining pressure in the plastic zone is different from those in the existing studies. According to the variation of critical plastic shear strain of the strain-softening rock mass influenced by the confining pressure，a modified criterion was presented to determine whether the rock mass resides within the plastic residual zone. A nonlinear dilatancy model was introduced to account for the confining pressure and the critical plastic shear strain. The plastic softening and residual zones were divided according to a certain radial stress increment. The stress and strain components are obtained based on Hoek-Brown failure criterion with the finite difference method. In order to discuss the influence of the confining pressure on the rock mass stability，four nonlinear mechanical models were established according to whether the critical shear strain or dilatancy coefficient was changed or not. The critical plastic shear strain，the dilatancy coefficient and the rock mass deformation in the plastic softening and residual zones were further studied under the four models. The calculated results show that for lower geological strength index(GSI)，the stress and strain states considering the confining pressure distinguish greatly from those not considering it. A reduction of the critical plastic shear strain restrains the dilatancy behaviour of surrounding rock mass near the opening surface to a certain extent.
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Received: 25 December 2013
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2014, Vol. 33 
