Interaction between yielding tunnel support and strain-softening rock mass based on the three-dimensional strength criterion

The "yield-resist" combined support measure is a widely employed control measure in soft rock tunnels for controlling large deformation, particularly in high geostress conditions. For strain-softening rock masses, the strength parameters in the plastic zone are coupled with the support reaction. Due to the complexity of the interaction mechanism between yielding support and strain-softening surrounding rock, the majority of current solutions are based on the plane-strain model. However, the advancement of the tunnel is a three-dimensional problem. Therefore, the longitudinal effect is worthy of discussion when analyzing the mechanical behaviors of strain-softening rock and yielding support. A new two-stage method is proposed to describe the interaction between strain-softening rock mass and yielding support based on the generalized Zhang-Zhu (GZZ) strength criterion. Firstly, a simplified mechanical model of the yielding support structure is suggested to describe the mechanical response of the surrounding rock and support. Subsequently, a semi-analytical solution to three-dimensional ground-support interaction is proposed, taking into account the longitudinal effect. The results of the proposed solution are compared with those of a finite element simulation, and a high degree of agreement is observed. Finally, the mechanical behaviors of different yielding supports are discussed. The findings indicate that postponing the support timing by means of yielding technologies is essential, as otherwise the support would bear a very large load. The second stage of support reaction can be significantly reduced by implementing the "control-yield-resist" (CYR) support. The research offers novel insights and methodologies for investigating the three-dimensional interaction between the surrounding rock and various tunnel supports in high geostress conditions.