Theoretical Study on the Rock-support Interaction for Deep Tunnel Based on Unified Strength Criterion

The interaction between surrounding rock and support structure is fundamental for support structure design and tunnel stability evaluation, closely related to underground engineering safety and economy. A strain-softening model based on Unified Strength Criteria (USC) is employed to characterize deep rock masses, considering intermediate principal stress effects on rock mechanical behavior. Under the assumption of axisymmetric plane strain, a new mechanical model for rock-support interaction is established. A corresponding solution method is proposed and validated by numerical simulation results, existing analytical models and field datasets. Parameter studies were conducted to investigate the effects of intermediate principal stress and supporting time on rock-support interaction. The findings indicate that the intermediate principal stress has a significant impact on the stability of the surrounding rock and the load-sharing behavior of the support structure. The increasing intermediate principal stress significantly reduces both tunnel wall displacement and support load, with a Stress Effect Factor (SEF) demonstrating up to a 28.1% reduction in tunnel wall deformation and a 12.6% reduction in support load when transitioning from the traditional Mohr-Coulomb criterion (the intermediate principal stress effect coefficient b =0) to a double shear strength criterion ( b =1). The proposed model and solution method provide a comprehensive and accurate approach to analyzing rock-support interaction in deep tunnels, offering valuable insights for tunnel design and support structure optimization.