Abstract:

In geotechnical engineering, many types of rock masses behave in a strain-softening way. It is not easy to get the closed form solution when strength parameters change in the strain-softening process. Literature review shows that the strain-softening problem has not been sufficiently analyzed within the framework of the classical theory of elastoplasticity. Based on the characteristics of strain-softening material in which the strength parameters change while the plastic strain increases, a new method for solving strain-softening problems is proposed. In the proposed numerical scheme, stress-strain curve in the strain-softening stage is approximated in a stepwise way; and the processes of the strain-softening is simplified as a series of stress drop and plastic flow during the increase of plastic strain. Therefore, modeling a strain-softening problem becomes a series of brittle-plastic analysis. The approach is employed to examine the circular opening excavation in a homogeneous and isotropic rock mass subjected to a hydrostatic in situ stress. The effect of lining on the plastic region and deformation in the surrounding rock mass is analyzed; and the influence of strain-softening behaviour is also discussed. Numerical results indicate that it is unsafe to ignore the strength decrease when tunnel excavation and liner installation are carried out in the strain-softening rock mass.

Key words: strain-softening, brittle-plastic model, circular tunnel, numerical solution, yield criterion