A modified strain-softening model with multi-post-peak behaviours and its application in circular tunnel

• Published in: Engineering geology 2018-06, Vol.240, p.21-33
• Main Authors: Wu, Xuezhen, Jiang, Yujing, Guan, Zhenchang
• Format: Article
• Language: English
• Subjects: Confining pressure; Post-peak behaviour; Residual strength; Semi-analytical solution; Strain-softening model
• ISSN: 0013-7952; 1872-6917
• DOI: 10.1016/j.enggeo.2018.03.031

A large number of laboratory experiments have shown that the rocks in post-peak state present strain-softening behaviour under low confining pressure, and gradually evolved into elastic-perfectly plastic with the increasing of confining pressure. Neither the elastic-perfectly plastic model nor the strain-softening model can accurately describe the behaviour of rock mass surrounding the deep buried excavations. In this paper, a modified strain-softening model was proposed to describe the non-linear evolution of residual strength under the influence of confining pressure. The new model can realize the gradually transition from strain-softening behaviour to elastic-perfectly plastic behaviour with the increasing of confining pressure. The equivalent residual strength was defined to quantify the strength of rocks in post-peak stage. The parameters involved in the model were estimated via non-linear regression analysis upon a series of stress-strain curves. Based on the plane strain axial symmetry assumption and the incremental theory of plasticity, equilibrium equations and compatibility equations of rock mass around a circular tunnel were deduced. The equations were implemented in the Visual Basic development environment, and a semi-analytical solution was obtained. The influence of post-failure behaviour of rock mass was demonstrated through an illustrative case. The distributions of stress, displacement and transitional strength around the tunnel were presented. The differences between the elastic-perfectly plastic model, the strain-softening model and the new model were estimated quantitatively. In addition, the validity of semi-analytical solution was verified by numerical simulations. Parameters analysis showed that the tunnel convergence was influenced by the post-peak behaviour of rock mass dramatically. •A modified strain-softening model was proposed to describe the multi-post-peak behaviours of rock mass.•The new model can realize the gradually transition from strain-softening behaviour to elastic-perfectly plastic behaviour.•The influence of post-peak behaviour of rock mass on the tunnel convergence was demonstrated through an illustrative case.•Parameters analysis showed that the post-peak behaviour of rock mass influence the tunnel convergence dramatically.