Research on Mechanical Characteristics and Failure Modes of Interbedded Rock Mass with Varying Dip Angles under High In-Situ Stress

This study investigates the mechanical behavior and failure mechanisms of soft-hard interbedded tunnel under high in-situ stress, where interfacial joint planes reduce overall strength and induce anisotropy, leading to asymmetric large deformations during excavation that jeopardize construction safety and long-term operational stability. Focusing on the Jianshan Tunnel along the Zhonglan section of the Yinlan High-Speed Railway, we integrated field testing, laboratory experiments, and numerical simulations to analyze the mechanical response of interbedded rock masses at varying dip angles under high stress. Key findings include:①Field stress measurements at 342.57 m depth revealed a maximum horizontal principal stress of 12.40 MPa, with principal stress relationships SH > SV > Sh;②Laboratory tests demonstrated that the mechanical properties of interbedded rock masses are governed by the soft layer at low dip angles, by the interfacial planes at medium angles, and by the hard layer at high angles, exhibiting distinct failure modes: tensile splitting, shear failure, and composite failure, respectively;③ Numerical simulations classified surrounding rock deformation into four zones based on horizontal displacement evolution: slow-development, rapid-development, stabilization, and attenuation zones, with peak asymmetric displacement occurring at medium dip angles where minor eccentric tension and major eccentric compression regions form in supporting structures. These results provide critical insights for deformation control technologies and analogous engineering projects.