Abstract: To address the challenge of effectively controlling asymmetric large deformation induced by strong anisotropy during tunnel construction in steeply dipping layered rock mass under high geostress, existing research has primarily focused on the deformation phenomena of anisotropic layered rock or isolated failure modes, often resulting in a lack of targeted support countermeasures. Taking the steeply dipping layered phyllite section of the Wutaishan tunnel as the engineering background, this study employs a combination of numerical simulation using the "main rock layer-weak interlayer" composite modeling technique and field measurements to systematically investigate the spatial distribution characteristics, failure modes, and mechanical response of support structures in steeply dipping layered surrounding rock. An asymmetric active support strategy combining "long and short rock bolts" based on deformation characteristic zoning is proposed. The main findings are as follows: (1) Under the combination of rock stratum occurrence and in-situ stress, the surrounding rock deformation exhibits pronounced spatial asymmetry centered at the left spandrel. Settlement and horizontal displacement on the left side far exceed those on the right, and the disparity increases progressively with excavation. The plastic zone is primarily concentrated at the left spandrel and right haunch, indicating that the failure mechanism is controlled by the occurrence of steeply dipping strata. (2) In the conventional symmetric support system, compressive stress concentration occurs at the left spandrel, leading to local failure of the support structure. (3) The proposed asymmetric support scheme considerably reduces settlement and horizontal displacement at the left spandrel, and prominently alleviates stress concentration within the support system. (4) Field tests confirm the effectiveness of the proposed scheme. The maximum displacement on the tunnel′s left side is substantially reduced, and the evolution trend of bolt stress agrees with the numerical predictions. The results demonstrate that a differentiated asymmetric support strategy, based on deformation characteristics, is an effective approach for safely controlling deformation in high-speed railway tunnels constructed in steeply dipping layered rock masses.

Key words: high-speed railway tunnel, layered rock mass, asymmetric large deformation, deformation characteristics, numerical simulation, asymmetric support, field testing