Mechanisms of interaction and influence zone partitioning of high geo-stress twin tunnels in complex mountainous regions

In challenging mountainous regions under high geo-stress, the construction of twin tunnels faces unique interaction issues, which is a systemic risk arising from the coupling of stress fields, surrounding rock conditions, and twin-tunnel clear spacings. Compared to single tunnels, the disaster mechanisms and evolution patterns are more complex. Existing studies and standards on the classification of interaction degrees between twin tunnels remain insufficient. Due to the singularity of geological conditions, vagueness in the scope of influence, and lack of consideration for geo-stress levels, adequate support for the design and construction of twin tunnels under multivariate geotechnical conditions in challenging mountainous regions is not provided. This study focuses on the interaction patterns and influence zone partitioning of high geo-stress twin tunnels under multivariate geotechnical conditions. By integrating scaled model tests with numerical simulations, this study employs the plastic zone and secondary stress field distribution from numerical results as qualitative indicators, while using maximum tunnel peripheral displacement, maximum principal stress, and asymmetry coefficient as quantitative metrics. Additionally, failure patterns and structural stress patterns from model tests are used as supplementary evidence to comprehensively assess the interaction degree of twin tunnels. Based on these findings, the interaction patterns after excavation of high geo-stress twin tunnels are proposed, along with a classification standard suitable for multi-geological conditions. The interaction effects are categorized into four levels: severe, moderate, minor, and none. In engineering applications, appropriate twin-tunnel categories can be selected based on specific geo-stress and surrounding rock conditions to achieve better design rationality and economic efficiency.